OpenCV笔记（一）-XML文件读写

平台： ubuntu10.04 + OpenCV2.3 + cmake 

1. XML、YAML文件的打开和关闭

XML\YAML文件在OpenCV中的数据结构为FileStorage，打开操作例如：

string filename = "test.xml";  
FileStorage fs(filename, FileStorage::WRITE);  
\\或者
fs.open(filename, FileStorage::WRITE);  

// 文件读写模式
// file storage mode
 enum
    {
        READ=0, //! read mode
        WRITE=1, //! write mode
        APPEND=2 //! append mode
    };


文件关闭操作会在FileStorage结构销毁时自动进行，但也可调用如下函数实现
fs.release();  


2.文本和数字的输入和输出

写入文件使用  <<  运算符，例如：
fs << "iterationNr" << 100;  


读取文件，使用 >> 运算符，例如
int itNr;  
fs["iterationNr"] >> itNr;  
itNr = (int) fs["iterationNr"];  




3. OpenCV数据结构的输入和输出，和基本的C++形式相同

Mat R = Mat_<uchar >::eye (3, 3),  
T = Mat_<double>::zeros(3, 1);  
fs << "R" << R; // Write cv::Mat  
fs << "T" << T;  
fs["R"] >> R; // Read cv::Mat  
fs["T"] >> T;  


4. vector（arrays） 和 maps的输入和输出
vector要注意在第一个元素前加上“[”，在最后一个元素前加上"]"。例如：

fs << "strings" << "["; // text - string sequence  
fs << "image1.jpg" << "Awesomeness" << "baboon.jpg";  
fs << "]"; // close sequence  

对于map结构的操作使用的符号是"{"和"}"，例如：

fs << "Mapping"; // text - mapping  
fs << "{" << "One" << 1;  
fs << "Two" << 2 << "}";  


读取这些结构的时候，会用到FileNode和FileNodeIterator数据结构。对FileStorage类的[]操作符会返回FileNode数据类型，对于一连串的node，可以使用FileNodeIterator结构，例如：
FileNode n = fs["strings"]; // Read string sequence - Get node  
if (n.type() != FileNode::SEQ)  
{  
cerr << "strings is not a sequence! FAIL" << endl;  
return 1;  
}  
FileNodeIterator it = n.begin(), it_end = n.end(); // Go through the node  
for (; it != it_end; ++it)  
cout << (string)*it << endl;  


//！FileNode的类型
//! 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)
    };


5. 文件读写源码
### xml2.cpp
#############################################################################
// XML/YAML File Storage Class.
// 
// The class describes an object associated with XML or YAML file.
// It can be used to store data to such a file or read and decode the data.
// 
// The storage is organized as a tree of nested sequences (or lists) and mappings.
// Sequence is a heterogenious array, which elements are accessed by indices or sequentially using an iterator.
// Mapping is analogue of std::map or C structure, which elements are accessed by names.
// The most top level structure is a mapping.
// Leaves of the file storage tree are integers, floating-point numbers and text strings. 
// 
// For example, the following code:
#include"opencv2/core/core.hpp"
#include<iostream>
#include<string>
using namespace std;
using namespace cv;
 
int main(int agc, char** agv)
{
// open file storage for writing. Type of the file is determined from the extension
{
FileStorage fs("test.xml", 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 << "]" << "}";
}
 
// open file storage for reading.
// Type of the file is determined from the content, not the extension
{
FileStorage fs("test.xml", FileStorage::READ);
int test_int = (int)fs["test_int"];
double test_real = (double)fs["test_real"];
string test_string = (string)fs["test_string"];
cout << "test_int " << test_int << " test_real " << test_real << " test_string " << test_string << endl;
 
Mat M;
fs["test_mat"] >> M;
cout << "test_mat " << M << endl;
 
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"];
 
cout << "test_list" << endl;
cout << "tl0 " << tl0 << " tl1 " << tl1 << " tl2 " << tl2 << " tl3 " << tl3 << " tl4 " << tl4 << endl;
cout << "tl5 " << " month " << month << " day " << day << " year " << year << endl;
 
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"];
 
cout << "test_map " << " x " << x << " y " << y << " width " << width << " height " << height << endl;
 
int lbp_val = 0;
FileNodeIterator it = tm["lbp"].begin();
for(int k = 0; k < 8; k++, ++it)
{
lbp_val |= ((int)*it) << k;
}
cout << "blp " << lbp_val << endl;


 
}
return 0;
}
######################################################################


6、XML文件 test.xml
###########################################
<?xml version="1.0"?>
<opencv_storage>
<test_int>5</test_int>
<test_real>3.1000000000000001e+00</test_real>
<test_string>ABCDEFGH</test_string>
<test_mat type_id="opencv-matrix">
  <rows>3</rows>
  <cols>3</cols>
  <dt>f</dt>
  <data>
    1. 0. 0. 0. 1. 0. 0. 0. 1.</data></test_mat>
<test_list>
  1.0000000000000000e-13 2 3.1415926535897931e+00 -3435345
  "2-502 2-029 3egegeg"
  <_><month>12</month>
    <day>31</day>
    <year>1969</year></_></test_list>
<test_map>
  <x>1</x>
  <y>2</y>
  <width>100</width>
  <height>200</height>
  <lbp>
    0 1 1 0 1 1 0 1</lbp></test_map>
</opencv_storage>
##########################################
7、YML文件 tet.yml 运行时需将Filename改为test.yml
##########################################
%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 ]
#########################################


8、CMakeList.txt文件 
########################################
PROJECT(xml)


CMAKE_MINIMUM_REQUIRED(VERSION 2.6)
if(COMMAND cmake_policy)
      cmake_policy(SET CMP0003 NEW)
endif(COMMAND cmake_policy)


FIND_PACKAGE( OpenCV REQUIRED )


# Declare the target (an executable)
ADD_EXECUTABLE(xml  xml.cpp)


TARGET_LINK_LIBRARIES(xml ${OpenCV_LIBS})


#MESSAGE(STATUS "OpenCV_LIBS: ${OpenCV_LIBS}")
#################################################


编译执行：
cd currentPath
cmake -Unix 
make 
./xml2