Dynamic Structures

CvMemStorage

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CvMemStorage

Growing memory storage.

typedef struct CvMemStorage
{
    struct CvMemBlock* bottom;/* first allocated block */
    struct CvMemBlock* top; /* the current memory block - top of the stack */
    struct CvMemStorage* parent; /* borrows new blocks from */
    int block_size; /* block size */
    int free_space; /* free space in the ``top`` block (in bytes) */
} CvMemStorage;

Memory storage is a low-level structure used to store dynamicly growing data structures such as sequences, contours, graphs, subdivisions, etc. It is organized as a list of memory blocks of equal size - bottom field is the beginning of the list of blocks and top is the currently used block, but not necessarily the last block of the list. All blocks between bottom and top , not including the latter, are considered fully occupied; all blocks between top and the last block, not including top , are considered free and top itself is partly ocupied - free_space contains the number of free bytes left in the end of top .

A new memory buffer that may be allocated explicitly by MemStorageAlloc function or implicitly by higher-level functions, such as SeqPush , GraphAddEdge , etc., always starts in the end of the current block if it fits there. After allocation, free_space is decremented by the size of the allocated buffer plus some padding to keep the proper alignment. When the allocated buffer does not fit into the available portion of top , the next storage block from the list is taken as top and free_space is reset to the whole block size prior to the allocation.

If there are no more free blocks, a new block is allocated (or borrowed from the parent, see CreateChildMemStorage ) and added to the end of list. Thus, the storage behaves as a stack with bottom indicating bottom of the stack and the pair ( top , free_space ) indicating top of the stack. The stack top may be saved via SaveMemStoragePos , restored via RestoreMemStoragePos , or reset via ClearStorage .

CvMemBlock

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CvMemBlock

Memory storage block.

typedef struct CvMemBlock
{
    struct CvMemBlock* prev;
    struct CvMemBlock* next;
} CvMemBlock;

The structure CvMemBlock represents a single block of memory storage. The actual data in the memory blocks follows the header, that is, the byte of the memory block can be retrieved with the expression ((char*)(mem_block_ptr+1))[i] . However, there is normally no need to access the storage structure fields directly.

CvMemStoragePos

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CvMemStoragePos

Memory storage position.

typedef struct CvMemStoragePos
{
    CvMemBlock* top;
    int free_space;
} CvMemStoragePos;

The structure described above stores the position of the stack top that can be saved via SaveMemStoragePos and restored via RestoreMemStoragePos .

CvSeq

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CvSeq

Growable sequence of elements.

#define CV_SEQUENCE_FIELDS() \
    int flags; /* micsellaneous flags */ \
    int header_size; /* size of sequence header */ \
    struct CvSeq* h_prev; /* previous sequence */ \
    struct CvSeq* h_next; /* next sequence */ \
    struct CvSeq* v_prev; /* 2nd previous sequence */ \
    struct CvSeq* v_next; /* 2nd next sequence */ \
    int total; /* total number of elements */ \
    int elem_size;/* size of sequence element in bytes */ \
    char* block_max;/* maximal bound of the last block */ \
    char* ptr; /* current write pointer */ \
    int delta_elems; /* how many elements allocated when the sequence grows
                        (sequence granularity) */ \
    CvMemStorage* storage; /* where the seq is stored */ \
    CvSeqBlock* free_blocks; /* free blocks list */ \
    CvSeqBlock* first; /* pointer to the first sequence block */

typedef struct CvSeq
{
    CV_SEQUENCE_FIELDS()
} CvSeq;

The structure CvSeq is a base for all of OpenCV dynamic data structures.

Such an unusual definition via a helper macro simplifies the extension of the structure CvSeq with additional parameters. To extend CvSeq the user may define a new structure and put user-defined fields after all CvSeq fields that are included via the macro CV_SEQUENCE_FIELDS() .

There are two types of sequences - dense and sparse. The base type for dense sequences is CvSeq and such sequences are used to represent growable 1d arrays - vectors, stacks, queues, and deques. They have no gaps in the middle - if an element is removed from the middle or inserted into the middle of the sequence, the elements from the closer end are shifted. Sparse sequences have CvSet as a base class and they are discussed later in more detail. They are sequences of nodes; each may be either occupied or free as indicated by the node flag. Such sequences are used for unordered data structures such as sets of elements, graphs, hash tables and so forth.

The field header_size contains the actual size of the sequence header and should be greater than or equal to sizeof(CvSeq) .

The fields h_prev , h_next , v_prev , v_next can be used to create hierarchical structures from separate sequences. The fields h_prev and h_next point to the previous and the next sequences on the same hierarchical level, while the fields v_prev and v_next point to the previous and the next sequences in the vertical direction, that is, the parent and its first child. But these are just names and the pointers can be used in a different way.

The field first points to the first sequence block, whose structure is described below.

The field total contains the actual number of dense sequence elements and number of allocated nodes in a sparse sequence.

The field flags contains the particular dynamic type signature ( CV_SEQ_MAGIC_VAL for dense sequences and CV_SET_MAGIC_VAL for sparse sequences) in the highest 16 bits and miscellaneous information about the sequence. The lowest CV_SEQ_ELTYPE_BITS bits contain the ID of the element type. Most of sequence processing functions do not use element type but rather element size stored in elem_size . If a sequence contains the numeric data for one of the CvMat type then the element type matches to the corresponding CvMat element type, e.g., CV_32SC2 may be used for a sequence of 2D points, CV_32FC1 for sequences of floating-point values, etc. A CV_SEQ_ELTYPE(seq_header_ptr) macro retrieves the type of sequence elements. Processing functions that work with numerical sequences check that elem_size is equal to that calculated from the type element size. Besides CvMat compatible types, there are few extra element types defined in the cvtypes.h header:

Standard Types of Sequence Elements

#define CV_SEQ_ELTYPE_POINT          CV_32SC2  /* (x,y) */
#define CV_SEQ_ELTYPE_CODE           CV_8UC1   /* freeman code: 0..7 */
#define CV_SEQ_ELTYPE_GENERIC        0 /* unspecified type of
                                        sequence elements */
#define CV_SEQ_ELTYPE_PTR            CV_USRTYPE1 /* =6 */
#define CV_SEQ_ELTYPE_PPOINT         CV_SEQ_ELTYPE_PTR  /* &elem: pointer to
                                                element of other sequence */
#define CV_SEQ_ELTYPE_INDEX          CV_32SC1  /* #elem: index of element of
                                                      some other sequence */
#define CV_SEQ_ELTYPE_GRAPH_EDGE     CV_SEQ_ELTYPE_GENERIC  /* &next_o,
                                                  &next_d, &vtx_o, &vtx_d */
#define CV_SEQ_ELTYPE_GRAPH_VERTEX   CV_SEQ_ELTYPE_GENERIC  /* first_edge,
                                                                   &(x,y) */
#define CV_SEQ_ELTYPE_TRIAN_ATR      CV_SEQ_ELTYPE_GENERIC  /* vertex of the
                                                            binary tree   */
#define CV_SEQ_ELTYPE_CONNECTED_COMP CV_SEQ_ELTYPE_GENERIC  /* connected
                                                               component  */
#define CV_SEQ_ELTYPE_POINT3D        CV_32FC3  /* (x,y,z)  */

The next CV_SEQ_KIND_BITS bits specify the kind of sequence:

Standard Kinds of Sequences

/* generic (unspecified) kind of sequence */
#define CV_SEQ_KIND_GENERIC     (0 << CV_SEQ_ELTYPE_BITS)

/* dense sequence suntypes */
#define CV_SEQ_KIND_CURVE       (1 << CV_SEQ_ELTYPE_BITS)
#define CV_SEQ_KIND_BIN_TREE    (2 << CV_SEQ_ELTYPE_BITS)

/* sparse sequence (or set) subtypes */
#define CV_SEQ_KIND_GRAPH       (3 << CV_SEQ_ELTYPE_BITS)
#define CV_SEQ_KIND_SUBDIV2D    (4 << CV_SEQ_ELTYPE_BITS)

The remaining bits are used to identify different features specific to certain sequence kinds and element types. For example, curves made of points (CV_SEQ_KIND_CURVE|CV_SEQ_ELTYPE_POINT) , together with the flag CV_SEQ_FLAG_CLOSED , belong to the type CV_SEQ_POLYGON or, if other flags are used, to its subtype. Many contour processing functions check the type of the input sequence and report an error if they do not support this type. The file cvtypes.h stores the complete list of all supported predefined sequence types and helper macros designed to get the sequence type of other properties. The definition of the building blocks of sequences can be found below.

CvSeqBlock

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CvSeqBlock

Continuous sequence block.

typedef struct CvSeqBlock
{
    struct CvSeqBlock* prev; /* previous sequence block */
    struct CvSeqBlock* next; /* next sequence block */
    int start_index; /* index of the first element in the block +
    sequence->first->start_index */
    int count; /* number of elements in the block */
    char* data; /* pointer to the first element of the block */
} CvSeqBlock;

Sequence blocks make up a circular double-linked list, so the pointers prev and next are never NULL and point to the previous and the next sequence blocks within the sequence. It means that next of the last block is the first block and prev of the first block is the last block. The fields startIndex and count help to track the block location within the sequence. For example, if the sequence consists of 10 elements and splits into three blocks of 3, 5, and 2 elements, and the first block has the parameter startIndex = 2 , then pairs (startIndex, count) for the sequence blocks are (2,3), (5, 5), and (10, 2) correspondingly. The parameter startIndex of the first block is usually 0 unless some elements have been inserted at the beginning of the sequence.

CvSlice

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CvSlice

A sequence slice.

typedef struct CvSlice
{
    int start_index;
    int end_index;
} CvSlice;

inline CvSlice cvSlice( int start, int end );
#define CV_WHOLE_SEQ_END_INDEX 0x3fffffff
#define CV_WHOLE_SEQ  cvSlice(0, CV_WHOLE_SEQ_END_INDEX)

/* calculates the sequence slice length */
int cvSliceLength( CvSlice slice, const CvSeq* seq );

Some of functions that operate on sequences take a CvSlice slice parameter that is often set to the whole sequence (CV _ WHOLE _ SEQ) by default. Either of the startIndex and endIndex may be negative or exceed the sequence length, startIndex is inclusive, and endIndex is an exclusive boundary. If they are equal, the slice is considered empty (i.e., contains no elements). Because sequences are treated as circular structures, the slice may select a few elements in the end of a sequence followed by a few elements at the beginning of the sequence. For example, cvSlice(-2, 3) in the case of a 10-element sequence will select a 5-element slice, containing the pre-last (8th), last (9th), the very first (0th), second (1th) and third (2nd) elements. The functions normalize the slice argument in the following way: first, SliceLength is called to determine the length of the slice, then, startIndex of the slice is normalized similarly to the argument of GetSeqElem (i.e., negative indices are allowed). The actual slice to process starts at the normalized startIndex and lasts SliceLength elements (again, assuming the sequence is a circular structure).

If a function does not accept a slice argument, but you want to process only a part of the sequence, the sub-sequence may be extracted using the SeqSlice function, or stored into a continuous buffer with CvtSeqToArray (optionally, followed by MakeSeqHeaderForArray ).

CvSet

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CvSet

Collection of nodes.

typedef struct CvSetElem
{
    int flags; /* it is negative if the node is free and zero or positive otherwise */
    struct CvSetElem* next_free; /* if the node is free, the field is a
                                    pointer to next free node */
}
CvSetElem;

#define CV_SET_FIELDS()    \
    CV_SEQUENCE_FIELDS()   /* inherits from [#CvSeq CvSeq] */ \
    struct CvSetElem* free_elems; /* list of free nodes */

typedef struct CvSet
{
    CV_SET_FIELDS()
} CvSet;

The structure CvSet is a base for OpenCV sparse data structures.

As follows from the above declaration, CvSet inherits from CvSeq and it adds the free_elems field, which is a list of free nodes, to it. Every set node, whether free or not, is an element of the underlying sequence. While there are no restrictions on elements of dense sequences, the set (and derived structures) elements must start with an integer field and be able to fit CvSetElem structure, because these two fields (an integer followed by a pointer) are required for the organization of a node set with the list of free nodes. If a node is free, the flags field is negative (the most-significant bit, or MSB, of the field is set), and the next_free points to the next free node (the first free node is referenced by the free_elems field of CvSet ). And if a node is occupied, the flags field is positive and contains the node index that may be retrieved using the ( set_elem->flags & CV_SET_ELEM_IDX_MASK ) expressions, the rest of the node content is determined by the user. In particular, the occupied nodes are not linked as the free nodes are, so the second field can be used for such a link as well as for some different purpose. The macro CV_IS_SET_ELEM(set_elem_ptr) can be used to determined whether the specified node is occupied or not.

Initially the set and the list are empty. When a new node is requested from the set, it is taken from the list of free nodes, which is then updated. If the list appears to be empty, a new sequence block is allocated and all the nodes within the block are joined in the list of free nodes. Thus, the total field of the set is the total number of nodes both occupied and free. When an occupied node is released, it is added to the list of free nodes. The node released last will be occupied first.

In OpenCV CvSet is used for representing graphs ( CvGraph ), sparse multi-dimensional arrays ( CvSparseMat ), and planar subdivisions CvSubdiv2D .

CvGraph

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CvGraph

Oriented or unoriented weighted graph.

#define CV_GRAPH_VERTEX_FIELDS()    \
    int flags; /* vertex flags */   \
    struct CvGraphEdge* first; /* the first incident edge */

typedef struct CvGraphVtx
{
    CV_GRAPH_VERTEX_FIELDS()
}
CvGraphVtx;

#define CV_GRAPH_EDGE_FIELDS()      \
    int flags; /* edge flags */     \
    float weight; /* edge weight */ \
    struct CvGraphEdge* next[2]; /* the next edges in the incidence lists for staring (0) */ \
                                  /* and ending (1) vertices */ \
    struct CvGraphVtx* vtx[2]; /* the starting (0) and ending (1) vertices */

typedef struct CvGraphEdge
{
    CV_GRAPH_EDGE_FIELDS()
}
CvGraphEdge;

#define  CV_GRAPH_FIELDS()                  \
    CV_SET_FIELDS() /* set of vertices */   \
    CvSet* edges;   /* set of edges */

typedef struct CvGraph
{
    CV_GRAPH_FIELDS()
}
CvGraph;

The structure CvGraph is a base for graphs used in OpenCV.

The graph structure inherits from CvSet - which describes common graph properties and the graph vertices, and contains another set as a member - which describes the graph edges.

The vertex, edge, and the graph header structures are declared using the same technique as other extendible OpenCV structures - via macros, which simplify extension and customization of the structures. While the vertex and edge structures do not inherit from CvSetElem explicitly, they satisfy both conditions of the set elements: having an integer field in the beginning and fitting within the CvSetElem structure. The flags fields are used as for indicating occupied vertices and edges as well as for other purposes, for example, for graph traversal (see CreateGraphScanner et al.), so it is better not to use them directly.

The graph is represented as a set of edges each of which has a list of incident edges. The incidence lists for different vertices are interleaved to avoid information duplication as much as posssible.

The graph may be oriented or unoriented. In the latter case there is no distiction between the edge connecting vertex with vertex and the edge connecting vertex with vertex - only one of them can exist in the graph at the same moment and it represents both and edges.

CvGraphScanner

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CvGraphScanner

Graph traversal state.

typedef struct CvGraphScanner
{
    CvGraphVtx* vtx;       /* current graph vertex (or current edge origin) */
    CvGraphVtx* dst;       /* current graph edge destination vertex */
    CvGraphEdge* edge;     /* current edge */

    CvGraph* graph;        /* the graph */
    CvSeq*   stack;        /* the graph vertex stack */
    int      index;        /* the lower bound of certainly visited vertices */
    int      mask;         /* event mask */
}
CvGraphScanner;

The structure CvGraphScanner is used for depth-first graph traversal. See discussion of the functions below.

cvmacro Helper macro for a tree node type declaration.

The macro CV_TREE_NODE_FIELDS() is used to declare structures that can be organized into hierarchical strucutures (trees), such as CvSeq - the basic type for all dynamic structures. The trees created with nodes declared using this macro can be processed using the functions described below in this section.

CvTreeNodeIterator

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CvTreeNodeIterator

Opens existing or creates new file storage.

typedef struct CvTreeNodeIterator
{
    const void* node;
    int level;
    int max_level;
}
CvTreeNodeIterator;

#define CV_TREE_NODE_FIELDS(node_type)                          \
    int       flags;         /* micsellaneous flags */          \
    int       header_size;   /* size of sequence header */      \
    struct    node_type* h_prev; /* previous sequence */        \
    struct    node_type* h_next; /* next sequence */            \
    struct    node_type* v_prev; /* 2nd previous sequence */    \
    struct    node_type* v_next; /* 2nd next sequence */

The structure CvTreeNodeIterator is used to traverse trees. Each tree node should start with the certain fields which are defined by CV_TREE_NODE_FIELDS(...) macro. In C++ terms, each tree node should be a structure “derived” from

struct _BaseTreeNode
{
    CV_TREE_NODE_FIELDS(_BaseTreeNode);
}

CvSeq , CvSet , CvGraph and other dynamic structures derived from CvSeq comply with the requirement.

ClearGraph

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void cvClearGraph(CvGraph* graph)

Clears a graph.

Parameters:

• graph – Graph

The function removes all vertices and edges from a graph. The function has O(1) time complexity.

ClearMemStorage

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void cvClearMemStorage(CvMemStorage* storage)

Clears memory storage.

Parameters:

• storage – Memory storage

The function resets the top (free space boundary) of the storage to the very beginning. This function does not deallocate any memory. If the storage has a parent, the function returns all blocks to the parent.

ClearSeq

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void cvClearSeq(CvSeq* seq)

Clears a sequence.

Parameters:

• seq – Sequence

The function removes all elements from a sequence. The function does not return the memory to the storage block, but this memory is reused later when new elements are added to the sequence. The function has ‘O(1)’ time complexity.

ClearSet

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void cvClearSet(CvSet* setHeader)

Clears a set.

Parameters:

• setHeader – Cleared set

The function removes all elements from set. It has O(1) time complexity.

CloneGraph

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CvGraph* cvCloneGraph(const CvGraph* graph, CvMemStorage* storage)

Clones a graph.

Parameters:

• graph – The graph to copy
• storage – Container for the copy

The function creates a full copy of the specified graph. If the graph vertices or edges have pointers to some external data, it can still be shared between the copies. The vertex and edge indices in the new graph may be different from the original because the function defragments the vertex and edge sets.

CloneSeq

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CvSeq* cvCloneSeq(const CvSeq* seq, CvMemStorage* storage=NULL)

Creates a copy of a sequence.

Parameters:

• seq – Sequence
• storage – The destination storage block to hold the new sequence header and the copied data, if any. If it is NULL, the function uses the storage block containing the input sequence.

The function makes a complete copy of the input sequence and returns it.

The call

cvCloneSeq( seq, storage )

is equivalent to

cvSeqSlice( seq, CV_WHOLE_SEQ, storage, 1 )

CreateChildMemStorage

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CvMemStorage* cvCreateChildMemStorage(CvMemStorage* parent)

Creates child memory storage.

Parameters:

• parent – Parent memory storage

The function creates a child memory storage that is similar to simple memory storage except for the differences in the memory allocation/deallocation mechanism. When a child storage needs a new block to add to the block list, it tries to get this block from the parent. The first unoccupied parent block available is taken and excluded from the parent block list. If no blocks are available, the parent either allocates a block or borrows one from its own parent, if any. In other words, the chain, or a more complex structure, of memory storages where every storage is a child/parent of another is possible. When a child storage is released or even cleared, it returns all blocks to the parent. In other aspects, child storage is the same as simple storage.

Child storage is useful in the following situation. Imagine that the user needs to process dynamic data residing in a given storage area and put the result back to that same storage area. With the simplest approach, when temporary data is resided in the same storage area as the input and output data, the storage area will look as follows after processing:

Dynamic data processing without using child storage

That is, garbage appears in the middle of the storage. However, if one creates a child memory storage at the beginning of processing, writes temporary data there, and releases the child storage at the end, no garbage will appear in the source/destination storage:

Dynamic data processing using a child storage

CreateGraph

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CvGraph* cvCreateGraph(int graph_flags, int header_size, int vtx_size, int edge_size, CvMemStorage* storage)

Creates an empty graph.

Parameters:

• graph_flags – Type of the created graph. Usually, it is either CV_SEQ_KIND_GRAPH for generic unoriented graphs and CV_SEQ_KIND_GRAPH | CV_GRAPH_FLAG_ORIENTED for generic oriented graphs.
• header_size – Graph header size; may not be less than sizeof(CvGraph)
• vtx_size – Graph vertex size; the custom vertex structure must start with CvGraphVtx (use CV_GRAPH_VERTEX_FIELDS() )
• edge_size – Graph edge size; the custom edge structure must start with CvGraphEdge (use CV_GRAPH_EDGE_FIELDS() )
• storage – The graph container

The function creates an empty graph and returns a pointer to it.

CreateGraphScanner

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CvGraphScanner* cvCreateGraphScanner(CvGraph* graph, CvGraphVtx* vtx=NULL, int mask=CV_GRAPH_ALL_ITEMS)

Creates structure for depth-first graph traversal.

Parameters:

• graph – Graph
• vtx – Initial vertex to start from. If NULL, the traversal starts from the first vertex (a vertex with the minimal index in the sequence of vertices).
• mask –

  Event mask indicating which events are of interest to the user (where NextGraphItem function returns control to the user) It can be CV_GRAPH_ALL_ITEMS (all events are of interest) or a combination of the following flags:

  • CV_GRAPH_VERTEX stop at the graph vertices visited for the first time
  • CV_GRAPH_TREE_EDGE stop at tree edges ( tree edge is the edge connecting the last visited vertex and the vertex to be visited next)
  • CV_GRAPH_BACK_EDGE stop at back edges ( back edge is an edge connecting the last visited vertex with some of its ancestors in the search tree)
  • CV_GRAPH_FORWARD_EDGE stop at forward edges ( forward edge is an edge conecting the last visited vertex with some of its descendants in the search tree. The forward edges are only possible during oriented graph traversal)
  • CV_GRAPH_CROSS_EDGE stop at cross edges ( cross edge is an edge connecting different search trees or branches of the same tree. The cross edges are only possible during oriented graph traversal)
  • CV_GRAPH_ANY_EDGE stop at any edge ( tree, back, forward , and cross edges )
  • CV_GRAPH_NEW_TREE stop in the beginning of every new search tree. When the traversal procedure visits all vertices and edges reachable from the initial vertex (the visited vertices together with tree edges make up a tree), it searches for some unvisited vertex in the graph and resumes the traversal process from that vertex. Before starting a new tree (including the very first tree when cvNextGraphItem is called for the first time) it generates a CV_GRAPH_NEW_TREE event. For unoriented graphs, each search tree corresponds to a connected component of the graph.
  • CV_GRAPH_BACKTRACKING stop at every already visited vertex during backtracking - returning to already visited vertexes of the traversal tree.

The function creates a structure for depth-first graph traversal/search. The initialized structure is used in the NextGraphItem function - the incremental traversal procedure.

CreateMemStorage

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CvMemStorage* cvCreateMemStorage(int blockSize=0)

Creates memory storage.

Parameters:

• blockSize – Size of the storage blocks in bytes. If it is 0, the block size is set to a default value - currently it is about 64K.

The function creates an empty memory storage. See CvMemStorage description.

CreateSeq

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CvSeq* cvCreateSeq(int seqFlags, int headerSize, int elemSize, CvMemStorage* storage)

Creates a sequence.

Parameters:

• seqFlags – Flags of the created sequence. If the sequence is not passed to any function working with a specific type of sequences, the sequence value may be set to 0, otherwise the appropriate type must be selected from the list of predefined sequence types.
• headerSize – Size of the sequence header; must be greater than or equal to sizeof(CvSeq) . If a specific type or its extension is indicated, this type must fit the base type header.
• elemSize – Size of the sequence elements in bytes. The size must be consistent with the sequence type. For example, for a sequence of points to be created, the element type CV_SEQ_ELTYPE_POINT should be specified and the parameter elemSize must be equal to sizeof(CvPoint) .
• storage – Sequence location

The function creates a sequence and returns the pointer to it. The function allocates the sequence header in the storage block as one continuous chunk and sets the structure fields flags , elemSize , headerSize , and storage to passed values, sets delta_elems to the default value (that may be reassigned using the SetSeqBlockSize function), and clears other header fields, including the space following the first sizeof(CvSeq) bytes.

CreateSet

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CvSet* cvCreateSet(int set_flags, int header_size, int elem_size, CvMemStorage* storage)

Creates an empty set.

Parameters:

• set_flags – Type of the created set
• header_size – Set header size; may not be less than sizeof(CvSet)
• elem_size – Set element size; may not be less than CvSetElem
• storage – Container for the set

The function creates an empty set with a specified header size and element size, and returns the pointer to the set. This function is just a thin layer on top of CreateSeq .

CvtSeqToArray

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void* cvCvtSeqToArray(const CvSeq* seq, void* elements, CvSlice slice=CV_WHOLE_SEQ)

Copies a sequence to one continuous block of memory.

Parameters:

• seq – Sequence
• elements – Pointer to the destination array that must be large enough. It should be a pointer to data, not a matrix header.
• slice – The sequence portion to copy to the array

The function copies the entire sequence or subsequence to the specified buffer and returns the pointer to the buffer.

EndWriteSeq

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CvSeq* cvEndWriteSeq(CvSeqWriter* writer)

Finishes the process of writing a sequence.

Parameters:

• writer – Writer state

The function finishes the writing process and returns the pointer to the written sequence. The function also truncates the last incomplete sequence block to return the remaining part of the block to memory storage. After that, the sequence can be read and modified safely. See cvStartWriteSeq and cvStartAppendToSeq

FindGraphEdge

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CvGraphEdge* cvFindGraphEdge(const CvGraph* graph, int start_idx, int end_idx)

Finds an edge in a graph.

#define cvGraphFindEdge cvFindGraphEdge

param graph:Graph param start_idx:  Index of the starting vertex of the edge param end_idx:Index of the ending vertex of the edge. For an unoriented graph, the order of the vertex parameters does not matter.

The function finds the graph edge connecting two specified vertices and returns a pointer to it or NULL if the edge does not exist.

FindGraphEdgeByPtr

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CvGraphEdge* cvFindGraphEdgeByPtr(const CvGraph* graph, const CvGraphVtx* startVtx, const CvGraphVtx* endVtx)

Finds an edge in a graph by using its pointer.

#define cvGraphFindEdgeByPtr cvFindGraphEdgeByPtr

param graph:Graph param startVtx:Pointer to the starting vertex of the edge param endVtx:Pointer to the ending vertex of the edge. For an unoriented graph, the order of the vertex parameters does not matter.

The function finds the graph edge connecting two specified vertices and returns pointer to it or NULL if the edge does not exists.

FlushSeqWriter

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void cvFlushSeqWriter(CvSeqWriter* writer)

Updates sequence headers from the writer.

Parameters:

• writer – Writer state

The function is intended to enable the user to read sequence elements, whenever required, during the writing process, e.g., in order to check specific conditions. The function updates the sequence headers to make reading from the sequence possible. The writer is not closed, however, so that the writing process can be continued at any time. If an algorithm requires frequent flushes, consider using SeqPush instead.

GetGraphVtx

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CvGraphVtx* cvGetGraphVtx(CvGraph* graph, int vtx_idx)

Finds a graph vertex by using its index.

Parameters:

• graph – Graph
• vtx_idx – Index of the vertex

The function finds the graph vertex by using its index and returns the pointer to it or NULL if the vertex does not belong to the graph.

GetSeqElem

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char* cvGetSeqElem(const CvSeq* seq, int index)

Returns a pointer to a sequence element according to its index.

#define CV_GET_SEQ_ELEM( TYPE, seq, index )  (TYPE*)cvGetSeqElem( (CvSeq*)(seq), (index) )

param seq:Sequence param index:Index of element

The function finds the element with the given index in the sequence and returns the pointer to it. If the element is not found, the function returns 0. The function supports negative indices, where -1 stands for the last sequence element, -2 stands for the one before last, etc. If the sequence is most likely to consist of a single sequence block or the desired element is likely to be located in the first block, then the macro CV_GET_SEQ_ELEM( elemType, seq, index ) should be used, where the parameter elemType is the type of sequence elements ( CvPoint for example), the parameter seq is a sequence, and the parameter index is the index of the desired element. The macro checks first whether the desired element belongs to the first block of the sequence and returns it if it does; otherwise the macro calls the main function GetSeqElem . Negative indices always cause the GetSeqElem call. The function has O(1) time complexity assuming that the number of blocks is much smaller than the number of elements.

GetSeqReaderPos

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int cvGetSeqReaderPos(CvSeqReader* reader)

Returns the current reader position.

Parameters:

• reader – Reader state

The function returns the current reader position (within 0 ... reader->seq->total - 1).

GetSetElem

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CvSetElem* cvGetSetElem(const CvSet* setHeader, int index)

Finds a set element by its index.

Parameters:

• setHeader – Set
• index – Index of the set element within a sequence

The function finds a set element by its index. The function returns the pointer to it or 0 if the index is invalid or the corresponding node is free. The function supports negative indices as it uses GetSeqElem to locate the node.

GraphAddEdge

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int cvGraphAddEdge(CvGraph* graph, int start_idx, int end_idx, const CvGraphEdge* edge=NULL, CvGraphEdge** inserted_edge=NULL)

Adds an edge to a graph.

Parameters:

• graph – Graph
• start_idx – Index of the starting vertex of the edge
• end_idx – Index of the ending vertex of the edge. For an unoriented graph, the order of the vertex parameters does not matter.
• edge – Optional input parameter, initialization data for the edge
• inserted_edge – Optional output parameter to contain the address of the inserted edge

The function connects two specified vertices. The function returns 1 if the edge has been added successfully, 0 if the edge connecting the two vertices exists already and -1 if either of the vertices was not found, the starting and the ending vertex are the same, or there is some other critical situation. In the latter case (i.e., when the result is negative), the function also reports an error by default.

GraphAddEdgeByPtr

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int cvGraphAddEdgeByPtr(CvGraph* graph, CvGraphVtx* start_vtx, CvGraphVtx* end_vtx, const CvGraphEdge* edge=NULL, CvGraphEdge** inserted_edge=NULL)

Adds an edge to a graph by using its pointer.

Parameters:

• graph – Graph
• start_vtx – Pointer to the starting vertex of the edge
• end_vtx – Pointer to the ending vertex of the edge. For an unoriented graph, the order of the vertex parameters does not matter.
• edge – Optional input parameter, initialization data for the edge
• inserted_edge – Optional output parameter to contain the address of the inserted edge within the edge set

The function connects two specified vertices. The function returns 1 if the edge has been added successfully, 0 if the edge connecting the two vertices exists already, and -1 if either of the vertices was not found, the starting and the ending vertex are the same or there is some other critical situation. In the latter case (i.e., when the result is negative), the function also reports an error by default.

GraphAddVtx

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int cvGraphAddVtx(CvGraph* graph, const CvGraphVtx* vtx=NULL, CvGraphVtx** inserted_vtx=NULL)

Adds a vertex to a graph.

Parameters:

• graph – Graph
• vtx – Optional input argument used to initialize the added vertex (only user-defined fields beyond sizeof(CvGraphVtx) are copied)
• inserted_vertex – Optional output argument. If not NULL , the address of the new vertex is written here.

The function adds a vertex to the graph and returns the vertex index.

GraphEdgeIdx

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int cvGraphEdgeIdx(CvGraph* graph, CvGraphEdge* edge)

Returns the index of a graph edge.

Parameters:

• graph – Graph
• edge – Pointer to the graph edge

The function returns the index of a graph edge.

GraphRemoveEdge

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void cvGraphRemoveEdge(CvGraph* graph, int start_idx, int end_idx)

Removes an edge from a graph.

Parameters:

• graph – Graph
• start_idx – Index of the starting vertex of the edge
• end_idx – Index of the ending vertex of the edge. For an unoriented graph, the order of the vertex parameters does not matter.

The function removes the edge connecting two specified vertices. If the vertices are not connected [in that order], the function does nothing.

GraphRemoveEdgeByPtr

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void cvGraphRemoveEdgeByPtr(CvGraph* graph, CvGraphVtx* start_vtx, CvGraphVtx* end_vtx)

Removes an edge from a graph by using its pointer.

Parameters:

• graph – Graph
• start_vtx – Pointer to the starting vertex of the edge
• end_vtx – Pointer to the ending vertex of the edge. For an unoriented graph, the order of the vertex parameters does not matter.

The function removes the edge connecting two specified vertices. If the vertices are not connected [in that order], the function does nothing.

GraphRemoveVtx

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int cvGraphRemoveVtx(CvGraph* graph, int index)

Removes a vertex from a graph.

Parameters:

• graph – Graph
• vtx_idx – Index of the removed vertex

The function removes a vertex from a graph together with all the edges incident to it. The function reports an error if the input vertex does not belong to the graph. The return value is the number of edges deleted, or -1 if the vertex does not belong to the graph.

GraphRemoveVtxByPtr

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int cvGraphRemoveVtxByPtr(CvGraph* graph, CvGraphVtx* vtx)

Removes a vertex from a graph by using its pointer.

Parameters:

• graph – Graph
• vtx – Pointer to the removed vertex

The function removes a vertex from the graph by using its pointer together with all the edges incident to it. The function reports an error if the vertex does not belong to the graph. The return value is the number of edges deleted, or -1 if the vertex does not belong to the graph.

GraphVtxDegree

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int cvGraphVtxDegree(const CvGraph* graph, int vtxIdx)

Counts the number of edges indicent to the vertex.

Parameters:

• graph – Graph
• vtxIdx – Index of the graph vertex

The function returns the number of edges incident to the specified vertex, both incoming and outgoing. To count the edges, the following code is used:

CvGraphEdge* edge = vertex->first; int count = 0;
while( edge )
{
    edge = CV_NEXT_GRAPH_EDGE( edge, vertex );
    count++;
}

The macro CV_NEXT_GRAPH_EDGE( edge, vertex ) returns the edge incident to vertex that follows after edge .

GraphVtxDegreeByPtr

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int cvGraphVtxDegreeByPtr(const CvGraph* graph, const CvGraphVtx* vtx)

Finds an edge in a graph.

Parameters:

• graph – Graph
• vtx – Pointer to the graph vertex

The function returns the number of edges incident to the specified vertex, both incoming and outcoming.

GraphVtxIdx

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int cvGraphVtxIdx(CvGraph* graph, CvGraphVtx* vtx)

Returns the index of a graph vertex.

Parameters:

• graph – Graph
• vtx – Pointer to the graph vertex

The function returns the index of a graph vertex.

InitTreeNodeIterator

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void cvInitTreeNodeIterator(CvTreeNodeIterator* tree_iterator, const void* first, int max_level)

Initializes the tree node iterator.

Parameters:

• tree_iterator – Tree iterator initialized by the function
• first – The initial node to start traversing from
• max_level – The maximal level of the tree ( first node assumed to be at the first level) to traverse up to. For example, 1 means that only nodes at the same level as first should be visited, 2 means that the nodes on the same level as first and their direct children should be visited, and so forth.

The function initializes the tree iterator. The tree is traversed in depth-first order.

InsertNodeIntoTree

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void cvInsertNodeIntoTree(void* node, void* parent, void* frame)

Adds a new node to a tree.

Parameters:

• node – The inserted node
• parent – The parent node that is already in the tree
• frame – The top level node. If parent and frame are the same, the v_prev field of node is set to NULL rather than parent .

The function adds another node into tree. The function does not allocate any memory, it can only modify links of the tree nodes.

MakeSeqHeaderForArray

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CvSeq* cvMakeSeqHeaderForArray(int seq_type, int header_size, int elem_size, void* elements, int total, CvSeq* seq, CvSeqBlock* block)

Constructs a sequence header for an array.

Parameters:

• seq_type – Type of the created sequence
• header_size – Size of the header of the sequence. Parameter sequence must point to the structure of that size or greater
• elem_size – Size of the sequence elements
• elements – Elements that will form a sequence
• total – Total number of elements in the sequence. The number of array elements must be equal to the value of this parameter.
• seq – Pointer to the local variable that is used as the sequence header
• block – Pointer to the local variable that is the header of the single sequence block

The function initializes a sequence header for an array. The sequence header as well as the sequence block are allocated by the user (for example, on stack). No data is copied by the function. The resultant sequence will consists of a single block and have NULL storage pointer; thus, it is possible to read its elements, but the attempts to add elements to the sequence will raise an error in most cases.

MemStorageAlloc

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void* cvMemStorageAlloc(CvMemStorage* storage, size_t size)

Allocates a memory buffer in a storage block.

Parameters:

• storage – Memory storage
• size – Buffer size

The function allocates a memory buffer in a storage block. The buffer size must not exceed the storage block size, otherwise a runtime error is raised. The buffer address is aligned by CV_STRUCT_ALIGN=sizeof(double) (for the moment) bytes.

MemStorageAllocString

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CvString cvMemStorageAllocString(CvMemStorage* storage, const char* ptr, int len=-1)

Allocates a text string in a storage block.

typedef struct CvString
{
    int len;
    char* ptr;
}
CvString;

param storage:Memory storage param ptr:The string param len:Length of the string (not counting the ending NUL ) . If the parameter is negative, the function computes the length.

The function creates copy of the string in memory storage. It returns the structure that contains user-passed or computed length of the string and pointer to the copied string.

NextGraphItem

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int cvNextGraphItem(CvGraphScanner* scanner)

Executes one or more steps of the graph traversal procedure.

Parameters:

• scanner – Graph traversal state. It is updated by this function.

The function traverses through the graph until an event of interest to the user (that is, an event, specified in the mask in the CreateGraphScanner call) is met or the traversal is completed. In the first case, it returns one of the events listed in the description of the mask parameter above and with the next call it resumes the traversal. In the latter case, it returns CV_GRAPH_OVER (-1). When the event is CV_GRAPH_VERTEX , CV_GRAPH_BACKTRACKING , or CV_GRAPH_NEW_TREE , the currently observed vertex is stored in scanner-:math:`>`vtx . And if the event is edge-related, the edge itself is stored at scanner-:math:`>`edge , the previously visited vertex - at scanner-:math:`>`vtx and the other ending vertex of the edge - at scanner-:math:`>`dst .

NextTreeNode

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void* cvNextTreeNode(CvTreeNodeIterator* tree_iterator)

Returns the currently observed node and moves the iterator toward the next node.

Parameters:

• tree_iterator – Tree iterator initialized by the function

The function returns the currently observed node and then updates the iterator - moving it toward the next node. In other words, the function behavior is similar to the *p++ expression on a typical C pointer or C++ collection iterator. The function returns NULL if there are no more nodes.

PrevTreeNode

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void* cvPrevTreeNode(CvTreeNodeIterator* tree_iterator)

Returns the currently observed node and moves the iterator toward the previous node.

Parameters:

• tree_iterator – Tree iterator initialized by the function

The function returns the currently observed node and then updates the iterator - moving it toward the previous node. In other words, the function behavior is similar to the *p-- expression on a typical C pointer or C++ collection iterator. The function returns NULL if there are no more nodes.

ReleaseGraphScanner

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void cvReleaseGraphScanner(CvGraphScanner** scanner)

Completes the graph traversal procedure.

Parameters:

• scanner – Double pointer to graph traverser

The function completes the graph traversal procedure and releases the traverser state.

ReleaseMemStorage

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void cvReleaseMemStorage(CvMemStorage** storage)

Releases memory storage.

Parameters:

• storage – Pointer to the released storage

The function deallocates all storage memory blocks or returns them to the parent, if any. Then it deallocates the storage header and clears the pointer to the storage. All child storage associated with a given parent storage block must be released before the parent storage block is released.

RestoreMemStoragePos

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void cvRestoreMemStoragePos(CvMemStorage* storage, CvMemStoragePos* pos)

Restores memory storage position.

Parameters:

• storage – Memory storage
• pos – New storage top position

The function restores the position of the storage top from the parameter pos . This function and the function cvClearMemStorage are the only methods to release memory occupied in memory blocks. Note again that there is no way to free memory in the middle of an occupied portion of a storage block.

SaveMemStoragePos

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void cvSaveMemStoragePos(const CvMemStorage* storage, CvMemStoragePos* pos)

Saves memory storage position.

Parameters:

• storage – Memory storage
• pos – The output position of the storage top

The function saves the current position of the storage top to the parameter pos . The function cvRestoreMemStoragePos can further retrieve this position.

SeqElemIdx

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int cvSeqElemIdx(const CvSeq* seq, const void* element, CvSeqBlock** block=NULL)

Returns the index of a specific sequence element.

Parameters:

• seq – Sequence
• element – Pointer to the element within the sequence
• block – Optional argument. If the pointer is not NULL , the address of the sequence block that contains the element is stored in this location.

The function returns the index of a sequence element or a negative number if the element is not found.

SeqInsert

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char* cvSeqInsert(CvSeq* seq, int beforeIndex, void* element=NULL)

Inserts an element in the middle of a sequence.

Parameters:

• seq – Sequence
• beforeIndex – Index before which the element is inserted. Inserting before 0 (the minimal allowed value of the parameter) is equal to SeqPushFront and inserting before seq->total (the maximal allowed value of the parameter) is equal to SeqPush .
• element – Inserted element

The function shifts the sequence elements from the inserted position to the nearest end of the sequence and copies the element content there if the pointer is not NULL. The function returns a pointer to the inserted element.

SeqInsertSlice

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void cvSeqInsertSlice(CvSeq* seq, int beforeIndex, const CvArr* fromArr)

Inserts an array in the middle of a sequence.

Parameters:

• seq – Sequence
• slice – The part of the sequence to remove
• fromArr – The array to take elements from

The function inserts all fromArr array elements at the specified position of the sequence. The array fromArr can be a matrix or another sequence.

SeqInvert

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void cvSeqInvert(CvSeq* seq)

Reverses the order of sequence elements.

Parameters:

• seq – Sequence

The function reverses the sequence in-place - makes the first element go last, the last element go first and so forth.

SeqPop

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void cvSeqPop(CvSeq* seq, void* element=NULL)

Removes an element from the end of a sequence.

Parameters:

• seq – Sequence
• element – Optional parameter . If the pointer is not zero, the function copies the removed element to this location.

The function removes an element from a sequence. The function reports an error if the sequence is already empty. The function has O(1) complexity.

SeqPopFront

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void cvSeqPopFront(CvSeq* seq, void* element=NULL)

Removes an element from the beginning of a sequence.

Parameters:

• seq – Sequence
• element – Optional parameter. If the pointer is not zero, the function copies the removed element to this location.

The function removes an element from the beginning of a sequence. The function reports an error if the sequence is already empty. The function has O(1) complexity.

SeqPopMulti

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void cvSeqPopMulti(CvSeq* seq, void* elements, int count, int in_front=0)

Removes several elements from either end of a sequence.

Parameters:

• seq – Sequence
• elements – Removed elements
• count – Number of elements to pop
• in_front –

  The flags specifying which end of the modified sequence.

  • CV_BACK the elements are added to the end of the sequence
  • CV_FRONT the elements are added to the beginning of the sequence

The function removes several elements from either end of the sequence. If the number of the elements to be removed exceeds the total number of elements in the sequence, the function removes as many elements as possible.

SeqPush

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char* cvSeqPush(CvSeq* seq, void* element=NULL)

Adds an element to the end of a sequence.

Parameters:

• seq – Sequence
• element – Added element

The function adds an element to the end of a sequence and returns a pointer to the allocated element. If the input element is NULL, the function simply allocates a space for one more element.

The following code demonstrates how to create a new sequence using this function:

CvMemStorage* storage = cvCreateMemStorage(0);
CvSeq* seq = cvCreateSeq( CV_32SC1, /* sequence of integer elements */
                          sizeof(CvSeq), /* header size - no extra fields */
                          sizeof(int), /* element size */
                          storage /* the container storage */ );
int i;
for( i = 0; i < 100; i++ )
{
    int* added = (int*)cvSeqPush( seq, &i );
    printf( "
}

...
/* release memory storage in the end */
cvReleaseMemStorage( &storage );

The function has O(1) complexity, but there is a faster method for writing large sequences (see StartWriteSeq and related functions).

SeqPushFront

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char* cvSeqPushFront(CvSeq* seq, void* element=NULL)

Adds an element to the beginning of a sequence.

Parameters:

• seq – Sequence
• element – Added element

The function is similar to SeqPush but it adds the new element to the beginning of the sequence. The function has O(1) complexity.

SeqPushMulti

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void cvSeqPushMulti(CvSeq* seq, void* elements, int count, int in_front=0)

Pushes several elements to either end of a sequence.

Parameters:

• seq – Sequence
• elements – Added elements
• count – Number of elements to push
• in_front –

  The flags specifying which end of the modified sequence.

  • CV_BACK the elements are added to the end of the sequence
  • CV_FRONT the elements are added to the beginning of the sequence

The function adds several elements to either end of a sequence. The elements are added to the sequence in the same order as they are arranged in the input array but they can fall into different sequence blocks.

SeqRemove

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void cvSeqRemove(CvSeq* seq, int index)

Removes an element from the middle of a sequence.

Parameters:

• seq – Sequence
• index – Index of removed element

The function removes elements with the given index. If the index is out of range the function reports an error. An attempt to remove an element from an empty sequence is a special case of this situation. The function removes an element by shifting the sequence elements between the nearest end of the sequence and the index -th position, not counting the latter.

SeqRemoveSlice

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void cvSeqRemoveSlice(CvSeq* seq, CvSlice slice)

Removes a sequence slice.

Parameters:

• seq – Sequence
• slice – The part of the sequence to remove

The function removes a slice from the sequence.

SeqSearch

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char* cvSeqSearch(CvSeq* seq, const void* elem, CvCmpFunc func, int is_sorted, int* elem_idx, void* userdata=NULL)

Searches for an element in a sequence.

Parameters:

• seq – The sequence
• elem – The element to look for
• func – The comparison function that returns negative, zero or positive value depending on the relationships among the elements (see also SeqSort )
• is_sorted – Whether the sequence is sorted or not
• elem_idx – Output parameter; index of the found element
• userdata – The user parameter passed to the compasion function; helps to avoid global variables in some cases

/* a < b ? -1 : a > b ? 1 : 0 */
typedef int (CV_CDECL* CvCmpFunc)(const void* a, const void* b, void* userdata);

The function searches for the element in the sequence. If the sequence is sorted, a binary O(log(N)) search is used; otherwise, a simple linear search is used. If the element is not found, the function returns a NULL pointer and the index is set to the number of sequence elements if a linear search is used, or to the smallest index i, seq(i)>elem .

SeqSlice

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CvSeq* cvSeqSlice(const CvSeq* seq, CvSlice slice, CvMemStorage* storage=NULL, int copy_data=0)

Makes a separate header for a sequence slice.

Parameters:

• seq – Sequence
• slice – The part of the sequence to be extracted
• storage – The destination storage block to hold the new sequence header and the copied data, if any. If it is NULL, the function uses the storage block containing the input sequence.
• copy_data – The flag that indicates whether to copy the elements of the extracted slice ( copy_data!=0 ) or not ( copy_data=0 )

The function creates a sequence that represents the specified slice of the input sequence. The new sequence either shares the elements with the original sequence or has its own copy of the elements. So if one needs to process a part of sequence but the processing function does not have a slice parameter, the required sub-sequence may be extracted using this function.

SeqSort

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void cvSeqSort(CvSeq* seq, CvCmpFunc func, void* userdata=NULL)

Sorts sequence element using the specified comparison function.

/* a < b ? -1 : a > b ? 1 : 0 */
typedef int (CV_CDECL* CvCmpFunc)(const void* a, const void* b, void* userdata);

param seq:The sequence to sort param func:The comparison function that returns a negative, zero, or positive value depending on the relationships among the elements (see the above declaration and the example below) - a similar function is used by qsort from C runline except that in the latter, userdata is not used param userdata:The user parameter passed to the compasion function; helps to avoid global variables in some cases

The function sorts the sequence in-place using the specified criteria. Below is an example of using this function:

/* Sort 2d points in top-to-bottom left-to-right order */
static int cmp_func( const void* _a, const void* _b, void* userdata )
{
    CvPoint* a = (CvPoint*)_a;
    CvPoint* b = (CvPoint*)_b;
    int y_diff = a->y - b->y;
    int x_diff = a->x - b->x;
    return y_diff ? y_diff : x_diff;
}

...

CvMemStorage* storage = cvCreateMemStorage(0);
CvSeq* seq = cvCreateSeq( CV_32SC2, sizeof(CvSeq), sizeof(CvPoint), storage );
int i;

for( i = 0; i < 10; i++ )
{
    CvPoint pt;
    pt.x = rand()
    pt.y = rand()
    cvSeqPush( seq, &pt );
}

cvSeqSort( seq, cmp_func, 0 /* userdata is not used here */ );

/* print out the sorted sequence */
for( i = 0; i < seq->total; i++ )
{
    CvPoint* pt = (CvPoint*)cvSeqElem( seq, i );
    printf( "(
}

cvReleaseMemStorage( &storage );

SetAdd

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int cvSetAdd(CvSet* setHeader, CvSetElem* elem=NULL, CvSetElem** inserted_elem=NULL)

Occupies a node in the set.

Parameters:

• setHeader – Set
• elem – Optional input argument, an inserted element. If not NULL, the function copies the data to the allocated node (the MSB of the first integer field is cleared after copying).
• inserted_elem – Optional output argument; the pointer to the allocated cell

The function allocates a new node, optionally copies input element data to it, and returns the pointer and the index to the node. The index value is taken from the lower bits of the flags field of the node. The function has O(1) complexity; however, there exists a faster function for allocating set nodes (see SetNew ).

SetNew

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CvSetElem* cvSetNew(CvSet* setHeader)

Adds an element to a set (fast variant).

Parameters:

• setHeader – Set

The function is an inline lightweight variant of SetAdd . It occupies a new node and returns a pointer to it rather than an index.

SetRemove

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void cvSetRemove(CvSet* setHeader, int index)

Removes an element from a set.

Parameters:

• setHeader – Set
• index – Index of the removed element

The function removes an element with a specified index from the set. If the node at the specified location is not occupied, the function does nothing. The function has O(1) complexity; however, SetRemoveByPtr provides a quicker way to remove a set element if it is located already.

SetRemoveByPtr

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void cvSetRemoveByPtr(CvSet* setHeader, void* elem)

Removes a set element based on its pointer.

Parameters:

• setHeader – Set
• elem – Removed element

The function is an inline lightweight variant of SetRemove that requires an element pointer. The function does not check whether the node is occupied or not - the user should take care of that.

SetSeqBlockSize

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void cvSetSeqBlockSize(CvSeq* seq, int deltaElems)

Sets up sequence block size.

Parameters:

• seq – Sequence
• deltaElems – Desirable sequence block size for elements

The function affects memory allocation granularity. When the free space in the sequence buffers has run out, the function allocates the space for deltaElems sequence elements. If this block immediately follows the one previously allocated, the two blocks are concatenated; otherwise, a new sequence block is created. Therefore, the bigger the parameter is, the lower the possible sequence fragmentation, but the more space in the storage block is wasted. When the sequence is created, the parameter deltaElems is set to the default value of about 1K. The function can be called any time after the sequence is created and affects future allocations. The function can modify the passed value of the parameter to meet memory storage constraints.

SetSeqReaderPos

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void cvSetSeqReaderPos(CvSeqReader* reader, int index, int is_relative=0)

Moves the reader to the specified position.

Parameters:

• reader – Reader state
• index – The destination position. If the positioning mode is used (see the next parameter), the actual position will be index mod reader->seq->total .
• is_relative – If it is not zero, then index is a relative to the current position

The function moves the read position to an absolute position or relative to the current position.

StartAppendToSeq

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void cvStartAppendToSeq(CvSeq* seq, CvSeqWriter* writer)

Initializes the process of writing data to a sequence.

Parameters:

• seq – Pointer to the sequence
• writer – Writer state; initialized by the function

The function initializes the process of writing data to a sequence. Written elements are added to the end of the sequence by using the CV_WRITE_SEQ_ELEM( written_elem, writer ) macro. Note that during the writing process, other operations on the sequence may yield an incorrect result or even corrupt the sequence (see description of FlushSeqWriter , which helps to avoid some of these problems).

StartReadSeq

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void cvStartReadSeq(const CvSeq* seq, CvSeqReader* reader, int reverse=0)

Initializes the process of sequential reading from a sequence.

Parameters:

• seq – Sequence
• reader – Reader state; initialized by the function
• reverse – Determines the direction of the sequence traversal. If reverse is 0, the reader is positioned at the first sequence element; otherwise it is positioned at the last element.

The function initializes the reader state. After that, all the sequence elements from the first one down to the last one can be read by subsequent calls of the macro CV_READ_SEQ_ELEM( read_elem, reader ) in the case of forward reading and by using CV_REV_READ_SEQ_ELEM( read_elem, reader ) in the case of reverse reading. Both macros put the sequence element to read_elem and move the reading pointer toward the next element. A circular structure of sequence blocks is used for the reading process, that is, after the last element has been read by the macro CV_READ_SEQ_ELEM , the first element is read when the macro is called again. The same applies to CV_REV_READ_SEQ_ELEM . There is no function to finish the reading process, since it neither changes the sequence nor creates any temporary buffers. The reader field ptr points to the current element of the sequence that is to be read next. The code below demonstrates how to use the sequence writer and reader.

CvMemStorage* storage = cvCreateMemStorage(0);
CvSeq* seq = cvCreateSeq( CV_32SC1, sizeof(CvSeq), sizeof(int), storage );
CvSeqWriter writer;
CvSeqReader reader;
int i;

cvStartAppendToSeq( seq, &writer );
for( i = 0; i < 10; i++ )
{
    int val = rand()
    CV_WRITE_SEQ_ELEM( val, writer );
    printf("
}
cvEndWriteSeq( &writer );

cvStartReadSeq( seq, &reader, 0 );
for( i = 0; i < seq->total; i++ )
{
    int val;
#if 1
    CV_READ_SEQ_ELEM( val, reader );
    printf("
#else /* alternative way, that is prefferable if sequence elements are large,
         or their size/type is unknown at compile time */
    printf("
    CV_NEXT_SEQ_ELEM( seq->elem_size, reader );
#endif
}
...

cvReleaseStorage( &storage );

StartWriteSeq

Comments from the Wiki

void cvStartWriteSeq(int seq_flags, int header_size, int elem_size, CvMemStorage* storage, CvSeqWriter* writer)

Creates a new sequence and initializes a writer for it.

Parameters:

• seq_flags – Flags of the created sequence. If the sequence is not passed to any function working with a specific type of sequences, the sequence value may be equal to 0; otherwise the appropriate type must be selected from the list of predefined sequence types.
• header_size – Size of the sequence header. The parameter value may not be less than sizeof(CvSeq) . If a certain type or extension is specified, it must fit within the base type header.
• elem_size – Size of the sequence elements in bytes; must be consistent with the sequence type. For example, if a sequence of points is created (element type CV_SEQ_ELTYPE_POINT ), then the parameter elem_size must be equal to sizeof(CvPoint) .
• storage – Sequence location
• writer – Writer state; initialized by the function

The function is a combination of CreateSeq and StartAppendToSeq . The pointer to the created sequence is stored at writer->seq and is also returned by the EndWriteSeq function that should be called at the end.

TreeToNodeSeq

Comments from the Wiki

CvSeq* cvTreeToNodeSeq(const void* first, int header_size, CvMemStorage* storage)

Gathers all node pointers to a single sequence.

Parameters:

• first – The initial tree node
• header_size – Header size of the created sequence (sizeof(CvSeq) is the most frequently used value)
• storage – Container for the sequence

The function puts pointers of all nodes reacheable from first into a single sequence. The pointers are written sequentially in the depth-first order.