XML/YAML Persistence ==================== .. highlight:: c .. index:: CvFileStorage .. _CvFileStorage: CvFileStorage ------------- `id=0.483064572953 Comments from the Wiki `__ .. ctype:: CvFileStorage File Storage. :: typedef struct CvFileStorage { ... // hidden fields } CvFileStorage; .. The structure :ref:`CvFileStorage` is a "black box" representation of the file storage associated with a file on disk. Several functions that are described below take ``CvFileStorage`` as inputs and allow theuser to save or to load hierarchical collections that consist of scalar values, standard CXCore objects (such as matrices, sequences, graphs), and user-defined objects. CXCore can read and write data in XML (http://www.w3c.org/XML) or YAML (http://www.yaml.org) formats. Below is an example of :math:`3 \times 3` floating-point identity matrix ``A`` , stored in XML and YAML files using CXCore functions: XML: \begin{verbatim} 3 3
f
1. 0. 0. 0. 1. 0. 0. 0. 1. \end{verbatim} YAML: \begin{verbatim} A: !!opencv-matrix rows: 3 cols: 3 dt: f data: [ 1., 0., 0., 0., 1., 0., 0., 0., 1.] \end{verbatim} As it can be seen from the examples, XML uses nested tags to represent hierarchy, while YAML uses indentation for that purpose (similar to the Python programming language). The same CXCore functions can read and write data in both formats; the particular format is determined by the extension of the opened file, .xml for XML files and .yml or .yaml for YAML. .. index:: CvFileNode .. _CvFileNode: CvFileNode ---------- `id=0.141364857291 Comments from the Wiki `__ .. ctype:: CvFileNode File Storage Node. :: /* file node type */ #define CV_NODE_NONE 0 #define CV_NODE_INT 1 #define CV_NODE_INTEGER CV_NODE_INT #define CV_NODE_REAL 2 #define CV_NODE_FLOAT CV_NODE_REAL #define CV_NODE_STR 3 #define CV_NODE_STRING CV_NODE_STR #define CV_NODE_REF 4 /* not used */ #define CV_NODE_SEQ 5 #define CV_NODE_MAP 6 #define CV_NODE_TYPE_MASK 7 /* optional flags */ #define CV_NODE_USER 16 #define CV_NODE_EMPTY 32 #define CV_NODE_NAMED 64 #define CV_NODE_TYPE(tag) ((tag) & CV_NODE_TYPE_MASK) #define CV_NODE_IS_INT(tag) (CV_NODE_TYPE(tag) == CV_NODE_INT) #define CV_NODE_IS_REAL(tag) (CV_NODE_TYPE(tag) == CV_NODE_REAL) #define CV_NODE_IS_STRING(tag) (CV_NODE_TYPE(tag) == CV_NODE_STRING) #define CV_NODE_IS_SEQ(tag) (CV_NODE_TYPE(tag) == CV_NODE_SEQ) #define CV_NODE_IS_MAP(tag) (CV_NODE_TYPE(tag) == CV_NODE_MAP) #define CV_NODE_IS_COLLECTION(tag) (CV_NODE_TYPE(tag) >= CV_NODE_SEQ) #define CV_NODE_IS_FLOW(tag) (((tag) & CV_NODE_FLOW) != 0) #define CV_NODE_IS_EMPTY(tag) (((tag) & CV_NODE_EMPTY) != 0) #define CV_NODE_IS_USER(tag) (((tag) & CV_NODE_USER) != 0) #define CV_NODE_HAS_NAME(tag) (((tag) & CV_NODE_NAMED) != 0) #define CV_NODE_SEQ_SIMPLE 256 #define CV_NODE_SEQ_IS_SIMPLE(seq) (((seq)->flags & CV_NODE_SEQ_SIMPLE) != 0) typedef struct CvString { int len; char* ptr; } CvString; /* all the keys (names) of elements in the readed file storage are stored in the hash to speed up the lookup operations */ typedef struct CvStringHashNode { unsigned hashval; CvString str; struct CvStringHashNode* next; } CvStringHashNode; /* basic element of the file storage - scalar or collection */ typedef struct CvFileNode { int tag; struct CvTypeInfo* info; /* type information (only for user-defined object, for others it is 0) */ union { double f; /* scalar floating-point number */ int i; /* scalar integer number */ CvString str; /* text string */ CvSeq* seq; /* sequence (ordered collection of file nodes) */ struct CvMap* map; /* map (collection of named file nodes) */ } data; } CvFileNode; .. The structure is used only for retrieving data from file storage (i.e., for loading data from the file). When data is written to a file, it is done sequentially, with minimal buffering. No data is stored in the file storage. In opposite, when data is read from a file, the whole file is parsed and represented in memory as a tree. Every node of the tree is represented by :ref:`CvFileNode` . The type of file node ``N`` can be retrieved as ``CV_NODE_TYPE(N->tag)`` . Some file nodes (leaves) are scalars: text strings, integers, or floating-point numbers. Other file nodes are collections of file nodes, which can be scalars or collections in their turn. There are two types of collections: sequences and maps (we use YAML notation, however, the same is true for XML streams). Sequences (do not mix them with :ref:`CvSeq` ) are ordered collections of unnamed file nodes; maps are unordered collections of named file nodes. Thus, elements of sequences are accessed by index ( :ref:`GetSeqElem` ), while elements of maps are accessed by name ( :ref:`GetFileNodeByName` ). The table below describes the different types of file nodes: .. table:: ============== =========================== ================================ Type ``CV_NODE_TYPE(node->tag)`` Value \ ============== =========================== ================================ Integer ``CV_NODE_INT`` ``node->data.i`` \ Floating-point ``CV_NODE_REAL`` ``node->data.f`` \ Text string ``CV_NODE_STR`` ``node->data.str.ptr`` \ Sequence ``CV_NODE_SEQ`` ``node->data.seq`` \ Map ``CV_NODE_MAP`` ``node->data.map`` (see below) \ ============== =========================== ================================ There is no need to access the ``map`` field directly (by the way, ``CvMap`` is a hidden structure). The elements of the map can be retrieved with the :ref:`GetFileNodeByName` function that takes a pointer to the "map" file node. A user (custom) object is an instance of either one of the standard CxCore types, such as :ref:`CvMat` , :ref:`CvSeq` etc., or any type registered with :ref:`RegisterTypeInfo` . Such an object is initially represented in a file as a map (as shown in XML and YAML example files above) after the file storage has been opened and parsed. Then the object can be decoded (coverted to native representation) by request - when a user calls the :ref:`Read` or :ref:`ReadByName` functions. .. index:: CvAttrList .. _CvAttrList: CvAttrList ---------- `id=0.406141021497 Comments from the Wiki `__ .. ctype:: CvAttrList List of attributes. :: typedef struct CvAttrList { const char** attr; /* NULL-terminated array of (attribute_name,attribute_value) pairs */ struct CvAttrList* next; /* pointer to next chunk of the attributes list */ } CvAttrList; /* initializes CvAttrList structure */ inline CvAttrList cvAttrList( const char** attr=NULL, CvAttrList* next=NULL ); /* returns attribute value or 0 (NULL) if there is no such attribute */ const char* cvAttrValue( const CvAttrList* attr, const char* attr_name ); .. In the current implementation, attributes are used to pass extra parameters when writing user objects (see :ref:`Write` ). XML attributes inside tags are not supported, aside from the object type specification ( ``type_id`` attribute). .. index:: CvTypeInfo .. _CvTypeInfo: CvTypeInfo ---------- `id=0.0823986071822 Comments from the Wiki `__ .. ctype:: CvTypeInfo Type information. :: typedef int (CV_CDECL *CvIsInstanceFunc)( const void* structPtr ); typedef void (CV_CDECL *CvReleaseFunc)( void** structDblPtr ); typedef void* (CV_CDECL *CvReadFunc)( CvFileStorage* storage, CvFileNode* node ); typedef void (CV_CDECL *CvWriteFunc)( CvFileStorage* storage, const char* name, const void* structPtr, CvAttrList attributes ); typedef void* (CV_CDECL *CvCloneFunc)( const void* structPtr ); typedef struct CvTypeInfo { int flags; /* not used */ int header_size; /* sizeof(CvTypeInfo) */ struct CvTypeInfo* prev; /* previous registered type in the list */ struct CvTypeInfo* next; /* next registered type in the list */ const char* type_name; /* type name, written to file storage */ /* methods */ CvIsInstanceFunc is_instance; /* checks if the passed object belongs to the type */ CvReleaseFunc release; /* releases object (memory etc.) */ CvReadFunc read; /* reads object from file storage */ CvWriteFunc write; /* writes object to file storage */ CvCloneFunc clone; /* creates a copy of the object */ } CvTypeInfo; .. The structure :ref:`CvTypeInfo` contains information about one of the standard or user-defined types. Instances of the type may or may not contain a pointer to the corresponding :ref:`CvTypeInfo` structure. In any case, there is a way to find the type info structure for a given object using the :ref:`TypeOf` function. Aternatively, type info can be found by type name using :ref:`FindType` , which is used when an object is read from file storage. The user can register a new type with :ref:`RegisterType` that adds the type information structure into the beginning of the type list. Thus, it is possible to create specialized types from generic standard types and override the basic methods. .. index:: Clone .. _Clone: Clone ----- `id=0.897451208844 Comments from the Wiki `__ .. cfunction:: void* cvClone( const void* structPtr ) Makes a clone of an object. :param structPtr: The object to clone The function finds the type of a given object and calls ``clone`` with the passed object. .. index:: EndWriteStruct .. _EndWriteStruct: EndWriteStruct -------------- `id=0.647507259457 Comments from the Wiki `__ .. cfunction:: void cvEndWriteStruct(CvFileStorage* fs) Ends the writing of a structure. :param fs: File storage The function finishes the currently written structure. .. index:: FindType .. _FindType: FindType -------- `id=0.146192503193 Comments from the Wiki `__ .. cfunction:: CvTypeInfo* cvFindType(const char* typeName) Finds a type by its name. :param typeName: Type name The function finds a registered type by its name. It returns NULL if there is no type with the specified name. .. index:: FirstType .. _FirstType: FirstType --------- `id=0.569051496879 Comments from the Wiki `__ .. cfunction:: CvTypeInfo* cvFirstType(void) Returns the beginning of a type list. The function returns the first type in the list of registered types. Navigation through the list can be done via the ``prev`` and ``next`` fields of the :ref:`CvTypeInfo` structure. .. index:: GetFileNode .. _GetFileNode: GetFileNode ----------- `id=0.751534799531 Comments from the Wiki `__ .. cfunction:: CvFileNode* cvGetFileNode( CvFileStorage* fs, CvFileNode* map, const CvStringHashNode* key, int createMissing=0 ) Finds a node in a map or file storage. :param fs: File storage :param map: The parent map. If it is NULL, the function searches a top-level node. If both ``map`` and ``key`` are NULLs, the function returns the root file node - a map that contains top-level nodes. :param key: Unique pointer to the node name, retrieved with :ref:`GetHashedKey` :param createMissing: Flag that specifies whether an absent node should be added to the map The function finds a file node. It is a faster version of :ref:`GetFileNodeByName` (see :ref:`GetHashedKey` discussion). Also, the function can insert a new node, if it is not in the map yet. .. index:: GetFileNodeByName .. _GetFileNodeByName: GetFileNodeByName ----------------- `id=0.610069416174 Comments from the Wiki `__ .. cfunction:: CvFileNode* cvGetFileNodeByName( const CvFileStorage* fs, const CvFileNode* map, const char* name) Finds a node in a map or file storage. :param fs: File storage :param map: The parent map. If it is NULL, the function searches in all the top-level nodes (streams), starting with the first one. :param name: The file node name The function finds a file node by ``name`` . The node is searched either in ``map`` or, if the pointer is NULL, among the top-level file storage nodes. Using this function for maps and :ref:`GetSeqElem` (or sequence reader) for sequences, it is possible to nagivate through the file storage. To speed up multiple queries for a certain key (e.g., in the case of an array of structures) one may use a combination of :ref:`GetHashedKey` and :ref:`GetFileNode` . .. index:: GetFileNodeName .. _GetFileNodeName: GetFileNodeName --------------- `id=0.822339513013 Comments from the Wiki `__ .. cfunction:: const char* cvGetFileNodeName( const CvFileNode* node ) Returns the name of a file node. :param node: File node The function returns the name of a file node or NULL, if the file node does not have a name or if ``node`` is ``NULL`` . .. index:: GetHashedKey .. _GetHashedKey: GetHashedKey ------------ `id=0.374505427001 Comments from the Wiki `__ .. cfunction:: CvStringHashNode* cvGetHashedKey( CvFileStorage* fs, const char* name, int len=-1, int createMissing=0 ) Returns a unique pointer for a given name. :param fs: File storage :param name: Literal node name :param len: Length of the name (if it is known apriori), or -1 if it needs to be calculated :param createMissing: Flag that specifies, whether an absent key should be added into the hash table The function returns a unique pointer for each particular file node name. This pointer can be then passed to the :ref:`GetFileNode` function that is faster than :ref:`GetFileNodeByName` because it compares text strings by comparing pointers rather than the strings' content. Consider the following example where an array of points is encoded as a sequence of 2-entry maps: :: points: - { x: 10, y: 10 } - { x: 20, y: 20 } - { x: 30, y: 30 } # ... .. Then, it is possible to get hashed "x" and "y" pointers to speed up decoding of the points. :: #include "cxcore.h" int main( int argc, char** argv ) { CvFileStorage* fs = cvOpenFileStorage( "points.yml", 0, CV_STORAGE_READ ); CvStringHashNode* x_key = cvGetHashedNode( fs, "x", -1, 1 ); CvStringHashNode* y_key = cvGetHashedNode( fs, "y", -1, 1 ); CvFileNode* points = cvGetFileNodeByName( fs, 0, "points" ); if( CV_NODE_IS_SEQ(points->tag) ) { CvSeq* seq = points->data.seq; int i, total = seq->total; CvSeqReader reader; cvStartReadSeq( seq, &reader, 0 ); for( i = 0; i < total; i++ ) { CvFileNode* pt = (CvFileNode*)reader.ptr; #if 1 /* faster variant */ CvFileNode* xnode = cvGetFileNode( fs, pt, x_key, 0 ); CvFileNode* ynode = cvGetFileNode( fs, pt, y_key, 0 ); assert( xnode && CV_NODE_IS_INT(xnode->tag) && ynode && CV_NODE_IS_INT(ynode->tag)); int x = xnode->data.i; // or x = cvReadInt( xnode, 0 ); int y = ynode->data.i; // or y = cvReadInt( ynode, 0 ); #elif 1 /* slower variant; does not use x_key & y_key */ CvFileNode* xnode = cvGetFileNodeByName( fs, pt, "x" ); CvFileNode* ynode = cvGetFileNodeByName( fs, pt, "y" ); assert( xnode && CV_NODE_IS_INT(xnode->tag) && ynode && CV_NODE_IS_INT(ynode->tag)); int x = xnode->data.i; // or x = cvReadInt( xnode, 0 ); int y = ynode->data.i; // or y = cvReadInt( ynode, 0 ); #else /* the slowest yet the easiest to use variant */ int x = cvReadIntByName( fs, pt, "x", 0 /* default value */ ); int y = cvReadIntByName( fs, pt, "y", 0 /* default value */ ); #endif CV_NEXT_SEQ_ELEM( seq->elem_size, reader ); printf(" } } cvReleaseFileStorage( &fs ); return 0; } .. Please note that whatever method of accessing a map you are using, it is still much slower than using plain sequences; for example, in the above example, it is more efficient to encode the points as pairs of integers in a single numeric sequence. .. index:: GetRootFileNode .. _GetRootFileNode: GetRootFileNode --------------- `id=0.0881886336977 Comments from the Wiki `__ .. cfunction:: CvFileNode* cvGetRootFileNode( const CvFileStorage* fs, int stream_index=0 ) Retrieves one of the top-level nodes of the file storage. :param fs: File storage :param stream_index: Zero-based index of the stream. See :ref:`StartNextStream` . In most cases, there is only one stream in the file; however, there can be several. The function returns one of the top-level file nodes. The top-level nodes do not have a name, they correspond to the streams that are stored one after another in the file storage. If the index is out of range, the function returns a NULL pointer, so all the top-level nodes may be iterated by subsequent calls to the function with ``stream_index=0,1,...`` , until the NULL pointer is returned. This function may be used as a base for recursive traversal of the file storage. .. index:: Load .. _Load: Load ---- `id=0.669837864208 Comments from the Wiki `__ .. cfunction:: void* cvLoad( const char* filename, CvMemStorage* storage=NULL, const char* name=NULL, const char** realName=NULL ) Loads an object from a file. :param filename: File name :param storage: Memory storage for dynamic structures, such as :ref:`CvSeq` or :ref:`CvGraph` . It is not used for matrices or images. :param name: Optional object name. If it is NULL, the first top-level object in the storage will be loaded. :param realName: Optional output parameter that will contain the name of the loaded object (useful if ``name=NULL`` ) The function loads an object from a file. It provides a simple interface to :ref:`Read` . After the object is loaded, the file storage is closed and all the temporary buffers are deleted. Thus, to load a dynamic structure, such as a sequence, contour, or graph, one should pass a valid memory storage destination to the function. .. index:: OpenFileStorage .. _OpenFileStorage: OpenFileStorage --------------- `id=0.879533341464 Comments from the Wiki `__ .. cfunction:: CvFileStorage* cvOpenFileStorage( const char* filename, CvMemStorage* memstorage, int flags) Opens file storage for reading or writing data. :param filename: Name of the file associated with the storage :param memstorage: Memory storage used for temporary data and for storing dynamic structures, such as :ref:`CvSeq` or :ref:`CvGraph` . If it is NULL, a temporary memory storage is created and used. :param flags: Can be one of the following: * **CV_STORAGE_READ** the storage is open for reading * **CV_STORAGE_WRITE** the storage is open for writing The function opens file storage for reading or writing data. In the latter case, a new file is created or an existing file is rewritten. The type of the read or written file is determined by the filename extension: ``.xml`` for ``XML`` and ``.yml`` or ``.yaml`` for ``YAML`` . The function returns a pointer to the :ref:`CvFileStorage` structure. .. index:: Read .. _Read: Read ---- `id=0.00484396193941 Comments from the Wiki `__ .. cfunction:: void* cvRead( CvFileStorage* fs, CvFileNode* node, CvAttrList* attributes=NULL ) Decodes an object and returns a pointer to it. :param fs: File storage :param node: The root object node :param attributes: Unused parameter The function decodes a user object (creates an object in a native representation from the file storage subtree) and returns it. The object to be decoded must be an instance of a registered type that supports the ``read`` method (see :ref:`CvTypeInfo` ). The type of the object is determined by the type name that is encoded in the file. If the object is a dynamic structure, it is created either in memory storage and passed to :ref:`OpenFileStorage` or, if a NULL pointer was passed, in temporary memory storage, which is released when :ref:`ReleaseFileStorage` is called. Otherwise, if the object is not a dynamic structure, it is created in a heap and should be released with a specialized function or by using the generic :ref:`Release` . .. index:: ReadByName .. _ReadByName: ReadByName ---------- `id=0.991047678837 Comments from the Wiki `__ .. cfunction:: void* cvReadByName( CvFileStorage* fs, const CvFileNode* map, const char* name, CvAttrList* attributes=NULL ) Finds an object by name and decodes it. :param fs: File storage :param map: The parent map. If it is NULL, the function searches a top-level node. :param name: The node name :param attributes: Unused parameter The function is a simple superposition of :ref:`GetFileNodeByName` and :ref:`Read` . .. index:: ReadInt .. _ReadInt: ReadInt ------- `id=0.440532441791 Comments from the Wiki `__ .. cfunction:: int cvReadInt( const CvFileNode* node, int defaultValue=0 ) Retrieves an integer value from a file node. :param node: File node :param defaultValue: The value that is returned if ``node`` is NULL The function returns an integer that is represented by the file node. If the file node is NULL, the ``defaultValue`` is returned (thus, it is convenient to call the function right after :ref:`GetFileNode` without checking for a NULL pointer). If the file node has type ``CV_NODE_INT`` , then ``node->data.i`` is returned. If the file node has type ``CV_NODE_REAL`` , then ``node->data.f`` is converted to an integer and returned. Otherwise the result is not determined. .. index:: ReadIntByName .. _ReadIntByName: ReadIntByName ------------- `id=0.921272136198 Comments from the Wiki `__ .. cfunction:: int cvReadIntByName( const CvFileStorage* fs, const CvFileNode* map, const char* name, int defaultValue=0 ) Finds a file node and returns its value. :param fs: File storage :param map: The parent map. If it is NULL, the function searches a top-level node. :param name: The node name :param defaultValue: The value that is returned if the file node is not found The function is a simple superposition of :ref:`GetFileNodeByName` and :ref:`ReadInt` . .. index:: ReadRawData .. _ReadRawData: ReadRawData ----------- `id=0.0291498172543 Comments from the Wiki `__ .. cfunction:: void cvReadRawData( const CvFileStorage* fs, const CvFileNode* src, void* dst, const char* dt) Reads multiple numbers. :param fs: File storage :param src: The file node (a sequence) to read numbers from :param dst: Pointer to the destination array :param dt: Specification of each array element. It has the same format as in :ref:`WriteRawData` . The function reads elements from a file node that represents a sequence of scalars. .. index:: ReadRawDataSlice .. _ReadRawDataSlice: ReadRawDataSlice ---------------- `id=0.655117920846 Comments from the Wiki `__ .. cfunction:: void cvReadRawDataSlice( const CvFileStorage* fs, CvSeqReader* reader, int count, void* dst, const char* dt ) Initializes file node sequence reader. :param fs: File storage :param reader: The sequence reader. Initialize it with :ref:`StartReadRawData` . :param count: The number of elements to read :param dst: Pointer to the destination array :param dt: Specification of each array element. It has the same format as in :ref:`WriteRawData` . The function reads one or more elements from the file node, representing a sequence, to a user-specified array. The total number of read sequence elements is a product of ``total`` and the number of components in each array element. For example, if dt= ``2if`` , the function will read :math:`\texttt{total} \times 3` sequence elements. As with any sequence, some parts of the file node sequence may be skipped or read repeatedly by repositioning the reader using :ref:`SetSeqReaderPos` . .. index:: ReadReal .. _ReadReal: ReadReal -------- `id=0.510390343877 Comments from the Wiki `__ .. cfunction:: double cvReadReal( const CvFileNode* node, double defaultValue=0. ) Retrieves a floating-point value from a file node. :param node: File node :param defaultValue: The value that is returned if ``node`` is NULL The function returns a floating-point value that is represented by the file node. If the file node is NULL, the ``defaultValue`` is returned (thus, it is convenient to call the function right after :ref:`GetFileNode` without checking for a NULL pointer). If the file node has type ``CV_NODE_REAL`` , then ``node->data.f`` is returned. If the file node has type ``CV_NODE_INT`` , then ``node-:math:`>`data.f`` is converted to floating-point and returned. Otherwise the result is not determined. .. index:: ReadRealByName .. _ReadRealByName: ReadRealByName -------------- `id=0.857568599741 Comments from the Wiki `__ .. cfunction:: double cvReadRealByName( const CvFileStorage* fs, const CvFileNode* map, const char* name, double defaultValue=0.) Finds a file node and returns its value. :param fs: File storage :param map: The parent map. If it is NULL, the function searches a top-level node. :param name: The node name :param defaultValue: The value that is returned if the file node is not found The function is a simple superposition of :ref:`GetFileNodeByName` and :ref:`ReadReal` . .. index:: ReadString .. _ReadString: ReadString ---------- `id=0.978604238894 Comments from the Wiki `__ .. cfunction:: const char* cvReadString( const CvFileNode* node, const char* defaultValue=NULL ) Retrieves a text string from a file node. :param node: File node :param defaultValue: The value that is returned if ``node`` is NULL The function returns a text string that is represented by the file node. If the file node is NULL, the ``defaultValue`` is returned (thus, it is convenient to call the function right after :ref:`GetFileNode` without checking for a NULL pointer). If the file node has type ``CV_NODE_STR`` , then ``node-:math:`>`data.str.ptr`` is returned. Otherwise the result is not determined. .. index:: ReadStringByName .. _ReadStringByName: ReadStringByName ---------------- `id=0.223166042039 Comments from the Wiki `__ .. cfunction:: const char* cvReadStringByName( const CvFileStorage* fs, const CvFileNode* map, const char* name, const char* defaultValue=NULL ) Finds a file node by its name and returns its value. :param fs: File storage :param map: The parent map. If it is NULL, the function searches a top-level node. :param name: The node name :param defaultValue: The value that is returned if the file node is not found The function is a simple superposition of :ref:`GetFileNodeByName` and :ref:`ReadString` . .. index:: RegisterType .. _RegisterType: RegisterType ------------ `id=0.653609593369 Comments from the Wiki `__ .. cfunction:: void cvRegisterType(const CvTypeInfo* info) Registers a new type. :param info: Type info structure The function registers a new type, which is described by ``info`` . The function creates a copy of the structure, so the user should delete it after calling the function. .. index:: Release .. _Release: Release ------- `id=0.570194424642 Comments from the Wiki `__ .. cfunction:: void cvRelease( void** structPtr ) Releases an object. :param structPtr: Double pointer to the object The function finds the type of a given object and calls ``release`` with the double pointer. .. index:: ReleaseFileStorage .. _ReleaseFileStorage: ReleaseFileStorage ------------------ `id=0.192035492124 Comments from the Wiki `__ .. cfunction:: void cvReleaseFileStorage(CvFileStorage** fs) Releases file storage. :param fs: Double pointer to the released file storage The function closes the file associated with the storage and releases all the temporary structures. It must be called after all I/O operations with the storage are finished. .. index:: Save .. _Save: Save ---- `id=0.237748213574 Comments from the Wiki `__ .. cfunction:: void cvSave( const char* filename, const void* structPtr, const char* name=NULL, const char* comment=NULL, CvAttrList attributes=cvAttrList()) Saves an object to a file. :param filename: File name :param structPtr: Object to save :param name: Optional object name. If it is NULL, the name will be formed from ``filename`` . :param comment: Optional comment to put in the beginning of the file :param attributes: Optional attributes passed to :ref:`Write` The function saves an object to a file. It provides a simple interface to :ref:`Write` . .. index:: StartNextStream .. _StartNextStream: StartNextStream --------------- `id=0.68752344308 Comments from the Wiki `__ .. cfunction:: void cvStartNextStream(CvFileStorage* fs) Starts the next stream. :param fs: File storage The function starts the next stream in file storage. Both YAML and XML support multiple "streams." This is useful for concatenating files or for resuming the writing process. .. index:: StartReadRawData .. _StartReadRawData: StartReadRawData ---------------- `id=0.00107156005523 Comments from the Wiki `__ .. cfunction:: void cvStartReadRawData( const CvFileStorage* fs, const CvFileNode* src, CvSeqReader* reader) Initializes the file node sequence reader. :param fs: File storage :param src: The file node (a sequence) to read numbers from :param reader: Pointer to the sequence reader The function initializes the sequence reader to read data from a file node. The initialized reader can be then passed to :ref:`ReadRawDataSlice` . .. index:: StartWriteStruct .. _StartWriteStruct: StartWriteStruct ---------------- `id=0.622157143994 Comments from the Wiki `__ .. cfunction:: void cvStartWriteStruct( CvFileStorage* fs, const char* name, int struct_flags, const char* typeName=NULL, CvAttrList attributes=cvAttrList( )) Starts writing a new structure. :param fs: File storage :param name: Name of the written structure. The structure can be accessed by this name when the storage is read. :param struct_flags: A combination one of the following values: * **CV_NODE_SEQ** the written structure is a sequence (see discussion of :ref:`CvFileStorage` ), that is, its elements do not have a name. * **CV_NODE_MAP** the written structure is a map (see discussion of :ref:`CvFileStorage` ), that is, all its elements have names. One and only one of the two above flags must be specified :param CV_NODE_FLOW: the optional flag that makes sense only for YAML streams. It means that the structure is written as a flow (not as a block), which is more compact. It is recommended to use this flag for structures or arrays whose elements are all scalars. :param typeName: Optional parameter - the object type name. In case of XML it is written as a ``type_id`` attribute of the structure opening tag. In the case of YAML it is written after a colon following the structure name (see the example in :ref:`CvFileStorage` description). Mainly it is used with user objects. When the storage is read, the encoded type name is used to determine the object type (see :ref:`CvTypeInfo` and :ref:`FindTypeInfo` ). :param attributes: This parameter is not used in the current implementation The function starts writing a compound structure (collection) that can be a sequence or a map. After all the structure fields, which can be scalars or structures, are written, :ref:`EndWriteStruct` should be called. The function can be used to group some objects or to implement the ``write`` function for a some user object (see :ref:`CvTypeInfo` ). .. index:: TypeOf .. _TypeOf: TypeOf ------ `id=0.790825181572 Comments from the Wiki `__ .. cfunction:: CvTypeInfo* cvTypeOf( const void* structPtr ) Returns the type of an object. :param structPtr: The object pointer The function finds the type of a given object. It iterates through the list of registered types and calls the ``is_instance`` function/method for every type info structure with that object until one of them returns non-zero or until the whole list has been traversed. In the latter case, the function returns NULL. .. index:: UnregisterType .. _UnregisterType: UnregisterType -------------- `id=0.308372872429 Comments from the Wiki `__ .. cfunction:: void cvUnregisterType( const char* typeName ) Unregisters the type. :param typeName: Name of an unregistered type The function unregisters a type with a specified name. If the name is unknown, it is possible to locate the type info by an instance of the type using :ref:`TypeOf` or by iterating the type list, starting from :ref:`FirstType` , and then calling ``cvUnregisterType(info->typeName)`` . .. index:: Write .. _Write: Write ----- `id=0.685599477914 Comments from the Wiki `__ .. cfunction:: void cvWrite( CvFileStorage* fs, const char* name, const void* ptr, CvAttrList attributes=cvAttrList() ) Writes a user object. :param fs: File storage :param name: Name of the written object. Should be NULL if and only if the parent structure is a sequence. :param ptr: Pointer to the object :param attributes: The attributes of the object. They are specific for each particular type (see the dicsussion below). The function writes an object to file storage. First, the appropriate type info is found using :ref:`TypeOf` . Then, the ``write`` method associated with the type info is called. Attributes are used to customize the writing procedure. The standard types support the following attributes (all the ``*dt`` attributes have the same format as in :ref:`WriteRawData` ): #. CvSeq * **header_dt** description of user fields of the sequence header that follow CvSeq, or CvChain (if the sequence is a Freeman chain) or CvContour (if the sequence is a contour or point sequence) * **dt** description of the sequence elements. * **recursive** if the attribute is present and is not equal to "0" or "false", the whole tree of sequences (contours) is stored. #. Cvgraph * **header_dt** description of user fields of the graph header that follows CvGraph; * **vertex_dt** description of user fields of graph vertices * **edge_dt** description of user fields of graph edges (note that the edge weight is always written, so there is no need to specify it explicitly) Below is the code that creates the YAML file shown in the ``CvFileStorage`` description: :: #include "cxcore.h" int main( int argc, char** argv ) { CvMat* mat = cvCreateMat( 3, 3, CV_32F ); CvFileStorage* fs = cvOpenFileStorage( "example.yml", 0, CV_STORAGE_WRITE ); cvSetIdentity( mat ); cvWrite( fs, "A", mat, cvAttrList(0,0) ); cvReleaseFileStorage( &fs ); cvReleaseMat( &mat ); return 0; } .. .. index:: WriteComment .. _WriteComment: WriteComment ------------ `id=0.671261599279 Comments from the Wiki `__ .. cfunction:: void cvWriteComment( CvFileStorage* fs, const char* comment, int eolComment) Writes a comment. :param fs: File storage :param comment: The written comment, single-line or multi-line :param eolComment: If non-zero, the function tries to put the comment at the end of current line. If the flag is zero, if the comment is multi-line, or if it does not fit at the end of the current line, the comment starts a new line. The function writes a comment into file storage. The comments are skipped when the storage is read, so they may be used only for debugging or descriptive purposes. .. index:: WriteFileNode .. _WriteFileNode: WriteFileNode ------------- `id=0.615303084023 Comments from the Wiki `__ .. cfunction:: void cvWriteFileNode( CvFileStorage* fs, const char* new_node_name, const CvFileNode* node, int embed ) Writes a file node to another file storage. :param fs: Destination file storage :param new_file_node: New name of the file node in the destination file storage. To keep the existing name, use :ref:`cvGetFileNodeName` :param node: The written node :param embed: If the written node is a collection and this parameter is not zero, no extra level of hiararchy is created. Instead, all the elements of ``node`` are written into the currently written structure. Of course, map elements may be written only to a map, and sequence elements may be written only to a sequence. The function writes a copy of a file node to file storage. Possible applications of the function are merging several file storages into one and conversion between XML and YAML formats. .. index:: WriteInt .. _WriteInt: WriteInt -------- `id=0.795390808983 Comments from the Wiki `__ .. cfunction:: void cvWriteInt( CvFileStorage* fs, const char* name, int value) Writes an integer value. :param fs: File storage :param name: Name of the written value. Should be NULL if and only if the parent structure is a sequence. :param value: The written value The function writes a single integer value (with or without a name) to the file storage. .. index:: WriteRawData .. _WriteRawData: WriteRawData ------------ `id=0.345095098504 Comments from the Wiki `__ .. cfunction:: void cvWriteRawData( CvFileStorage* fs, const void* src, int len, const char* dt ) Writes multiple numbers. :param fs: File storage :param src: Pointer to the written array :param len: Number of the array elements to write :param dt: Specification of each array element that has the following format ``([count]{'u'|'c'|'w'|'s'|'i'|'f'|'d'})...`` where the characters correspond to fundamental C types: * **u** 8-bit unsigned number * **c** 8-bit signed number * **w** 16-bit unsigned number * **s** 16-bit signed number * **i** 32-bit signed number * **f** single precision floating-point number * **d** double precision floating-point number * **r** pointer, 32 lower bits of which are written as a signed integer. The type can be used to store structures with links between the elements. ``count`` is the optional counter of values of a given type. For example, ``2if`` means that each array element is a structure of 2 integers, followed by a single-precision floating-point number. The equivalent notations of the above specification are ' ``iif`` ', ' ``2i1f`` ' and so forth. Other examples: ``u`` means that the array consists of bytes, and ``2d`` means the array consists of pairs of doubles. The function writes an array, whose elements consist of single or multiple numbers. The function call can be replaced with a loop containing a few :ref:`WriteInt` and :ref:`WriteReal` calls, but a single call is more efficient. Note that because none of the elements have a name, they should be written to a sequence rather than a map. .. index:: WriteReal .. _WriteReal: WriteReal --------- `id=0.671719141649 Comments from the Wiki `__ .. cfunction:: void cvWriteReal( CvFileStorage* fs, const char* name, double value ) Writes a floating-point value. :param fs: File storage :param name: Name of the written value. Should be NULL if and only if the parent structure is a sequence. :param value: The written value The function writes a single floating-point value (with or without a name) to file storage. Special values are encoded as follows: NaN (Not A Number) as .NaN, :math:`\pm \infty` as +.Inf (-.Inf). The following example shows how to use the low-level writing functions to store custom structures, such as termination criteria, without registering a new type. :: void write_termcriteria( CvFileStorage* fs, const char* struct_name, CvTermCriteria* termcrit ) { cvStartWriteStruct( fs, struct_name, CV_NODE_MAP, NULL, cvAttrList(0,0)); cvWriteComment( fs, "termination criteria", 1 ); // just a description if( termcrit->type & CV_TERMCRIT_ITER ) cvWriteInteger( fs, "max_iterations", termcrit->max_iter ); if( termcrit->type & CV_TERMCRIT_EPS ) cvWriteReal( fs, "accuracy", termcrit->epsilon ); cvEndWriteStruct( fs ); } .. .. index:: WriteString .. _WriteString: WriteString ----------- `id=0.171357578017 Comments from the Wiki `__ .. cfunction:: void cvWriteString( CvFileStorage* fs, const char* name, const char* str, int quote=0 ) Writes a text string. :param fs: File storage :param name: Name of the written string . Should be NULL if and only if the parent structure is a sequence. :param str: The written text string :param quote: If non-zero, the written string is put in quotes, regardless of whether they are required. Otherwise, if the flag is zero, quotes are used only when they are required (e.g. when the string starts with a digit or contains spaces). The function writes a text string to file storage.