OpenCV编程-FileStorage解析

OpenCV编程-FileStorage解析当保存浮点数据或XML/YML⽂件时，OpenCV的接⼝提供了FileStorage类。

开始XML & YAML I/O 分析：
下⾯贴上FileStorage类的源码。

class CV_EXPORTS_W FileStorage
{
public:
//! file storage mode
enum
{
READ=0, //! read mode
WRITE=1, //! write mode
APPEND=2, //! append mode
MEMORY=4,
FORMAT_MASK=(7<<3),
FORMAT_AUTO=0,
FORMAT_XML=(1<<3),
FORMAT_YAML=(2<<3)
};
enum
{
UNDEFINED=0,
VALUE_EXPECTED=1,
NAME_EXPECTED=2,
INSIDE_MAP=4
};
//! the default constructor
CV_WRAP FileStorage();
//! the full constructor that opens file storage for reading or writing
CV_WRAP FileStorage(const string& source, int flags, const string& encoding=string());
//! the constructor that takes pointer to the C FileStorage structure
FileStorage(CvFileStorage* fs);
//! the destructor. calls release()
virtual ~FileStorage();
//! opens file storage for reading or writing. The previous storage is closed with release()
CV_WRAP virtual bool open(const string& filename, int flags, const string& encoding=string());
//! returns true if the object is associated with currently opened file.
CV_WRAP virtual bool isOpened() const;
//! closes the file and releases all the memory buffers
CV_WRAP virtual void release();
//! closes the file, releases all the memory buffers and returns the text string
CV_WRAP string releaseAndGetString();
//! returns the first element of the top-level mapping
CV_WRAP FileNode getFirstTopLevelNode() const;
//! returns the top-level mapping. YAML supports multiple streams
CV_WRAP FileNode root(int streamidx=0) const;
//! returns the specified element of the top-level mapping
FileNode operator[](const string& nodename) const;
//! returns the specified element of the top-level mapping
CV_WRAP FileNode operator[](const char* nodename) const;
//! returns pointer to the underlying C FileStorage structure
CvFileStorage* operator *() { return fs; }
//! returns pointer to the underlying C FileStorage structure
const CvFileStorage* operator *() const { return fs; }
//! writes one or more numbers of the specified format to the currently written structure
void writeRaw( const string& fmt, const uchar* vec, size_t len );
//! writes the registered C structure (CvMat, CvMatND, CvSeq). See cvWrite()
void writeObj( const string& name, const void* obj );
void writeObj( const string& name, const void* obj );
//! returns the normalized object name for the specified file name
static string getDefaultObjectName(const string& filename);
Ptr<CvFileStorage> fs; //!< the underlying C FileStorage structure
string elname; //!< the currently written element
vector<char> structs; //!< the stack of written structures
int state; //!< the writer state
};
FileNode 存储XML或YAML⽂件中的每个节点，并⽤于读写。

class CV_EXPORTS_W_SIMPLE FileNode
{
public:
//! type of the file storage node
enum
{
NONE=0, //!< empty node
INT=1, //!< an integer
REAL=2, //!< floating-point number
FLOAT=REAL, //!< synonym or REAL
STR=3, //!< text string in UTF-8 encoding
STRING=STR, //!< synonym for STR
REF=4, //!< integer of size size_t. Typically used for storing complex dynamic structures where some elements reference the others SEQ=5, //!< sequence
MAP=6, //!< mapping
TYPE_MASK=7,
FLOW=8, //!< compact representation of a sequence or mapping. Used only by YAML writer
USER=16, //!< a registered object (e.g. a matrix)
EMPTY=32, //!< empty structure (sequence or mapping)
NAMED=64 //!< the node has a name (i.e. it is element of a mapping)
};
//! the default constructor
CV_WRAP FileNode();
//! the full constructor wrapping CvFileNode structure.
FileNode(const CvFileStorage* fs, const CvFileNode* node);
//! the copy constructor
FileNode(const FileNode& node);
//! returns element of a mapping node
FileNode operator[](const string& nodename) const;
//! returns element of a mapping node
CV_WRAP FileNode operator[](const char* nodename) const;
//! returns element of a sequence node
CV_WRAP FileNode operator[](int i) const;
//! returns type of the node
CV_WRAP int type() const;
//! returns true if the node is empty
CV_WRAP bool empty() const;
//! returns true if the node is a "none" object
CV_WRAP bool isNone() const;
//! returns true if the node is a sequence
CV_WRAP bool isSeq() const;
//! returns true if the node is a mapping
CV_WRAP bool isMap() const;
//! returns true if the node is an integer
CV_WRAP bool isInt() const;
//! returns true if the node is a floating-point number
CV_WRAP bool isReal() const;
//! returns true if the node is a text string
CV_WRAP bool isString() const;
CV_WRAP bool isString() const;
//! returns true if the node has a name
CV_WRAP bool isNamed() const;
//! returns the node name or an empty string if the node is nameless
CV_WRAP string name() const;
//! returns the number of elements in the node, if it is a sequence or mapping, or 1 otherwise.
CV_WRAP size_t size() const;
//! returns the node content as an integer. If the node stores floating-point number, it is rounded. operator int() const;
//! returns the node content as float
operator float() const;
//! returns the node content as double
operator double() const;
//! returns the node content as text string
operator string() const;
//! returns pointer to the underlying file node
CvFileNode* operator *();
//! returns pointer to the underlying file node
const CvFileNode* operator* () const;
//! returns iterator pointing to the first node element
FileNodeIterator begin() const;
//! returns iterator pointing to the element following the last node element
FileNodeIterator end() const;
//! reads node elements to the buffer with the specified format
void readRaw( const string& fmt, uchar* vec, size_t len ) const;
//! reads the registered object and returns pointer to it
void* readObj() const;
// do not use wrapper pointer classes for better efficiency
const CvFileStorage* fs;
const CvFileNode* node;
};
节点操作申明。

/*!
File Node Iterator
The class is used for iterating sequences (usually) and mappings.
*/
class CV_EXPORTS FileNodeIterator
{
public:
//! the default constructor
FileNodeIterator();
//! the full constructor set to the ofs-th element of the node
FileNodeIterator(const CvFileStorage* fs, const CvFileNode* node, size_t ofs=0);
//! the copy constructor
FileNodeIterator(const FileNodeIterator& it);
//! returns the currently observed element
FileNode operator *() const;
//! accesses the currently observed element methods
FileNode operator ->() const;
//! moves iterator to the next node
FileNodeIterator& operator ++ ();
//! moves iterator to the next node
FileNodeIterator operator ++ (int);
//! moves iterator to the previous node
FileNodeIterator& operator -- ();
//! moves iterator to the previous node
FileNodeIterator operator -- (int);
//! moves iterator forward by the specified offset (possibly negative)
FileNodeIterator& operator += (int ofs);
//! moves iterator backward by the specified offset (possibly negative)
FileNodeIterator& operator -= (int ofs);
//! reads the next maxCount elements (or less, if the sequence/mapping last element occurs earlier) to the buffer with the specified format FileNodeIterator& readRaw( const string& fmt, uchar* vec,
size_t maxCount=(size_t)INT_MAX );
const CvFileStorage* fs;
const CvFileNode* container;
CvSeqReader reader;
size_t remaining;
};
测试源码：
// open file storage for writing. Type of the file is determined from the extension
FileStorage fs("test.yml", FileStorage::WRITE);
fs << "test_int" << 5 << "test_real" << 3.1 << "test_string" << "ABCDEFGH";
fs << "test_mat" << Mat::eye(3,3,CV_32F);
fs << "test_list" << "[" << 0.0000000000001 << 2 << CV_PI << -3435345 << "2-502 2-029 3egegeg" <<
"{:" << "month" << 12 << "day" << 31 << "year" << 1969 << "}" << "]";
fs << "test_map" << "{" << "x" << 1 << "y" << 2 << "width" << 100 << "height" << 200 << "lbp" << "[:";
const uchar arr[] = {0, 1, 1, 0, 1, 1, 0, 1};
fs.writeRaw("u", arr, (int)(sizeof(arr)/sizeof(arr[0])));
fs << "]" << "}";
读⼊数据如下：
\verbatim
%YAML:1.0
test_int: 5
test_real: 3.1000000000000001e+00 test_string: ABCDEFGH
test_mat: !!opencv-matrix
rows: 3
cols: 3
dt: f
data: [ 1., 0., 0., 0., 1., 0., 0., 0., 1. ] test_list:
- 1.0000000000000000e-13
- 2
- 3.1415926535897931e+00
- -3435345
- "2-502 2-029 3egegeg"
- { month:12, day:31, year:1969 }
test_map:
x: 1
y: 2
width: 100
height: 200
lbp: [ 0, 1, 1, 0, 1, 1, 0, 1 ]
\endverbatim
读⼊源码：
// open file storage for reading.
// Type of the file is determined from the content, not the extension
FileStorage fs("test.yml", FileStorage::READ);
int test_int = (int)fs["test_int"];
double test_real = (double)fs["test_real"];
string test_string = (string)fs["test_string"];
Mat M;
fs["test_mat"] >> M;
FileNode tl = fs["test_list"];
CV_Assert(tl.type() == FileNode::SEQ && tl.size() == 6);
double tl0 = (double)tl[0];
int tl1 = (int)tl[1];
double tl2 = (double)tl[2];
int tl3 = (int)tl[3];
string tl4 = (string)tl[4];
CV_Assert(tl[5].type() == FileNode::MAP && tl[5].size() == 3);
int month = (int)tl[5]["month"];
int day = (int)tl[5]["day"];
int year = (int)tl[5]["year"];
FileNode tm = fs["test_map"];
int x = (int)tm["x"];
int y = (int)tm["y"];
int width = (int)tm["width"];
int height = (int)tm["height"];
int lbp_val = 0;
FileNodeIterator it = tm["lbp"].begin();
for(int k = 0; k < 8; k++, ++it)
lbp_val |= ((int)*it) << k;
1、XML和YAML可以嵌套的两种集合类型：映射（mappings）、序列（sequences）。

映射集合类似STL中的std::map和Python中的字典，序列集合类似STL中std::vector和 Python的序列；
2、当写⼊映射结构的数据时，节点的值（value）紧跟着节点的键(key)；当写⼊序列结构的数据时，逐⼀写⼊即可；
3、写⼊映射结构数据时，格式如下：fs << "{" << element_key << element_value << "}"
4、写⼊序列结构数据时，格式如下：fs << "[" << element_value << …… << "]"
5、写⼊映射、序列嵌套的数据时，以"{:"代替"{"，"[:" 代替 "["。