OpenCV  4.9.0-dev
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Public Types | Public Member Functions | Static Public Member Functions | Public Attributes | List of all members
cv::FileStorage Class Reference

XML/YAML/JSON file storage class that encapsulates all the information necessary for writing or reading data to/from a file. More...

#include <opencv2/core/persistence.hpp>

Collaboration diagram for cv::FileStorage:

Public Types

enum  Mode {
  READ = 0 ,
  WRITE = 1 ,
  APPEND = 2 ,
  MEMORY = 4 ,
  FORMAT_MASK = (7<<3) ,
  FORMAT_AUTO = 0 ,
  FORMAT_XML = (1<<3) ,
  FORMAT_YAML = (2<<3) ,
  FORMAT_JSON = (3<<3) ,
  BASE64 = 64 ,
  WRITE_BASE64 = BASE64 | WRITE
}
 file storage mode More...
 
enum  State {
  UNDEFINED = 0 ,
  VALUE_EXPECTED = 1 ,
  NAME_EXPECTED = 2 ,
  INSIDE_MAP = 4
}
 

Public Member Functions

 FileStorage ()
 The constructors.
 
 FileStorage (const String &filename, int flags, const String &encoding=String())
 
virtual ~FileStorage ()
 the destructor. calls release()
 
void endWriteStruct ()
 Finishes writing nested structure (should pair startWriteStruct())
 
FileNode getFirstTopLevelNode () const
 Returns the first element of the top-level mapping.
 
int getFormat () const
 Returns the current format.
 
virtual bool isOpened () const
 Checks whether the file is opened.
 
virtual bool open (const String &filename, int flags, const String &encoding=String())
 Opens a file.
 
FileNode operator[] (const char *nodename) const
 
FileNode operator[] (const String &nodename) const
 Returns the specified element of the top-level mapping.
 
virtual void release ()
 Closes the file and releases all the memory buffers.
 
virtual String releaseAndGetString ()
 Closes the file and releases all the memory buffers.
 
FileNode root (int streamidx=0) const
 Returns the top-level mapping.
 
void startWriteStruct (const String &name, int flags, const String &typeName=String())
 Starts to write a nested structure (sequence or a mapping).
 
void write (const String &name, const Mat &val)
 This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
 
void write (const String &name, const std::vector< String > &val)
 This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
 
void write (const String &name, const String &val)
 This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
 
void write (const String &name, double val)
 This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
 
void write (const String &name, int val)
 Simplified writing API to use with bindings.
 
void writeComment (const String &comment, bool append=false)
 Writes a comment.
 
void writeRaw (const String &fmt, const void *vec, size_t len)
 Writes multiple numbers.
 

Static Public Member Functions

static String getDefaultObjectName (const String &filename)
 Returns the normalized object name for the specified name of a file.
 

Public Attributes

std::string elname
 
Ptr< Impl > p
 
int state
 

Detailed Description

XML/YAML/JSON file storage class that encapsulates all the information necessary for writing or reading data to/from a file.

Examples
samples/cpp/filestorage.cpp, samples/cpp/tutorial_code/features2D/Homography/decompose_homography.cpp, samples/cpp/tutorial_code/features2D/Homography/homography_from_camera_displacement.cpp, and samples/cpp/tutorial_code/features2D/Homography/pose_from_homography.cpp.

Member Enumeration Documentation

◆ Mode

file storage mode

Enumerator
READ 

value, open the file for reading

WRITE 

value, open the file for writing

APPEND 

value, open the file for appending

MEMORY 

flag, read data from source or write data to the internal buffer (which is returned by FileStorage::release)

FORMAT_MASK 

mask for format flags

FORMAT_AUTO 

flag, auto format

FORMAT_XML 

flag, XML format

FORMAT_YAML 

flag, YAML format

FORMAT_JSON 

flag, JSON format

BASE64 

flag, write rawdata in Base64 by default. (consider using WRITE_BASE64)

WRITE_BASE64 

flag, enable both WRITE and BASE64

◆ State

Enumerator
UNDEFINED 
VALUE_EXPECTED 
NAME_EXPECTED 
INSIDE_MAP 

Constructor & Destructor Documentation

◆ FileStorage() [1/2]

cv::FileStorage::FileStorage ( )
Python:
cv.FileStorage() -> <FileStorage object>
cv.FileStorage(filename, flags[, encoding]) -> <FileStorage object>

The constructors.

The full constructor opens the file. Alternatively you can use the default constructor and then call FileStorage::open.

◆ FileStorage() [2/2]

cv::FileStorage::FileStorage ( const String filename,
int  flags,
const String encoding = String() 
)
Python:
cv.FileStorage() -> <FileStorage object>
cv.FileStorage(filename, flags[, encoding]) -> <FileStorage object>

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Opens a file.

See description of parameters in FileStorage::FileStorage. The method calls FileStorage::release before opening the file.

Parameters
filenameName of the file to open or the text string to read the data from. Extension of the file (.xml, .yml/.yaml or .json) determines its format (XML, YAML or JSON respectively). Also you can append .gz to work with compressed files, for example myHugeMatrix.xml.gz. If both FileStorage::WRITE and FileStorage::MEMORY flags are specified, source is used just to specify the output file format (e.g. mydata.xml, .yml etc.). A file name can also contain parameters. You can use this format, "*?base64" (e.g. "file.json?base64" (case sensitive)), as an alternative to FileStorage::BASE64 flag.
flagsMode of operation. One of FileStorage::Mode
encodingEncoding of the file. Note that UTF-16 XML encoding is not supported currently and you should use 8-bit encoding instead of it.

◆ ~FileStorage()

virtual cv::FileStorage::~FileStorage ( )
virtual

the destructor. calls release()

Member Function Documentation

◆ endWriteStruct()

void cv::FileStorage::endWriteStruct ( )
Python:
cv.FileStorage.endWriteStruct() -> None

Finishes writing nested structure (should pair startWriteStruct())

◆ getDefaultObjectName()

static String cv::FileStorage::getDefaultObjectName ( const String filename)
static

Returns the normalized object name for the specified name of a file.

Parameters
filenameName of a file
Returns
The normalized object name.

◆ getFirstTopLevelNode()

FileNode cv::FileStorage::getFirstTopLevelNode ( ) const
Python:
cv.FileStorage.getFirstTopLevelNode() -> retval

Returns the first element of the top-level mapping.

Returns
The first element of the top-level mapping.

◆ getFormat()

int cv::FileStorage::getFormat ( ) const
Python:
cv.FileStorage.getFormat() -> retval

Returns the current format.

Returns
The current format, see FileStorage::Mode

◆ isOpened()

virtual bool cv::FileStorage::isOpened ( ) const
virtual
Python:
cv.FileStorage.isOpened() -> retval

Checks whether the file is opened.

Returns
true if the object is associated with the current file and false otherwise. It is a good practice to call this method after you tried to open a file.
Examples
samples/cpp/filestorage.cpp.

◆ open()

virtual bool cv::FileStorage::open ( const String filename,
int  flags,
const String encoding = String() 
)
virtual
Python:
cv.FileStorage.open(filename, flags[, encoding]) -> retval

Opens a file.

See description of parameters in FileStorage::FileStorage. The method calls FileStorage::release before opening the file.

Parameters
filenameName of the file to open or the text string to read the data from. Extension of the file (.xml, .yml/.yaml or .json) determines its format (XML, YAML or JSON respectively). Also you can append .gz to work with compressed files, for example myHugeMatrix.xml.gz. If both FileStorage::WRITE and FileStorage::MEMORY flags are specified, source is used just to specify the output file format (e.g. mydata.xml, .yml etc.). A file name can also contain parameters. You can use this format, "*?base64" (e.g. "file.json?base64" (case sensitive)), as an alternative to FileStorage::BASE64 flag.
flagsMode of operation. One of FileStorage::Mode
encodingEncoding of the file. Note that UTF-16 XML encoding is not supported currently and you should use 8-bit encoding instead of it.

◆ operator[]() [1/2]

FileNode cv::FileStorage::operator[] ( const char *  nodename) const
Python:
cv.FileStorage.getNode(nodename) -> retval

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

◆ operator[]() [2/2]

FileNode cv::FileStorage::operator[] ( const String nodename) const
Python:
cv.FileStorage.getNode(nodename) -> retval

Returns the specified element of the top-level mapping.

Parameters
nodenameName of the file node.
Returns
Node with the given name.

◆ release()

virtual void cv::FileStorage::release ( )
virtual
Python:
cv.FileStorage.release() -> None

Closes the file and releases all the memory buffers.

Call this method after all I/O operations with the storage are finished.

◆ releaseAndGetString()

virtual String cv::FileStorage::releaseAndGetString ( )
virtual
Python:
cv.FileStorage.releaseAndGetString() -> retval

Closes the file and releases all the memory buffers.

Call this method after all I/O operations with the storage are finished. If the storage was opened for writing data and FileStorage::WRITE was specified

Examples
samples/cpp/filestorage.cpp.

◆ root()

FileNode cv::FileStorage::root ( int  streamidx = 0) const
Python:
cv.FileStorage.root([, streamidx]) -> retval

Returns the top-level mapping.

Parameters
streamidxZero-based index of the stream. In most cases there is only one stream in the file. However, YAML supports multiple streams and so there can be several.
Returns
The top-level mapping.

◆ startWriteStruct()

void cv::FileStorage::startWriteStruct ( const String name,
int  flags,
const String typeName = String() 
)
Python:
cv.FileStorage.startWriteStruct(name, flags[, typeName]) -> None

Starts to write a nested structure (sequence or a mapping).

Parameters
namename of the structure. When writing to sequences (a.k.a. "arrays"), pass an empty string.
flagstype of the structure (FileNode::MAP or FileNode::SEQ (both with optional FileNode::FLOW)).
typeNameoptional name of the type you store. The effect of setting this depends on the storage format. I.e. if the format has a specification for storing type information, this parameter is used.

◆ write() [1/5]

void cv::FileStorage::write ( const String name,
const Mat val 
)
Python:
cv.FileStorage.write(name, val) -> None

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

◆ write() [2/5]

void cv::FileStorage::write ( const String name,
const std::vector< String > &  val 
)
Python:
cv.FileStorage.write(name, val) -> None

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

◆ write() [3/5]

void cv::FileStorage::write ( const String name,
const String val 
)
Python:
cv.FileStorage.write(name, val) -> None

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

◆ write() [4/5]

void cv::FileStorage::write ( const String name,
double  val 
)
Python:
cv.FileStorage.write(name, val) -> None

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

◆ write() [5/5]

void cv::FileStorage::write ( const String name,
int  val 
)
Python:
cv.FileStorage.write(name, val) -> None

Simplified writing API to use with bindings.

Parameters
nameName of the written object. When writing to sequences (a.k.a. "arrays"), pass an empty string.
valValue of the written object.

◆ writeComment()

void cv::FileStorage::writeComment ( const String comment,
bool  append = false 
)
Python:
cv.FileStorage.writeComment(comment[, append]) -> None

Writes a comment.

The function writes a comment into file storage. The comments are skipped when the storage is read.

Parameters
commentThe written comment, single-line or multi-line
appendIf true, the function tries to put the comment at the end of current line. Else 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.

◆ writeRaw()

void cv::FileStorage::writeRaw ( const String fmt,
const void *  vec,
size_t  len 
)

Writes multiple numbers.

Writes one or more numbers of the specified format to the currently written structure. Usually it is more convenient to use operator << instead of this method.

Parameters
fmtSpecification of each array element, see format specification
vecPointer to the written array.
lenNumber of the uchar elements to write.

Member Data Documentation

◆ elname

std::string cv::FileStorage::elname

◆ p

Ptr<Impl> cv::FileStorage::p

◆ state

int cv::FileStorage::state

The documentation for this class was generated from the following file: