| OpenCV 5.0.0alpha Open Source Computer Vision

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samples/cpp/tutorial_code/core/file_input_output/file_input_output.cpp

A complete example using the FileStorage interface Check the corresponding tutorial for more details

#include <opencv2/core.hpp>
#include <iostream>
#include <string>
using namespace cv;
using namespace std;
static void help(char** av)
{
cout << endl
<< av[0] << " shows the usage of the OpenCV serialization functionality." << endl << endl
<< "usage: " << endl
<< av[0] << " [output file name] (default outputfile.yml.gz)" << endl << endl
<< "The output file may be XML (xml), YAML (yml/yaml), or JSON (json)." << endl
<< "You can even compress it by specifying this in its extension like xml.gz yaml.gz etc... " << endl
<< "With FileStorage you can serialize objects in OpenCV by using the << and >> operators" << endl
<< "For example: - create a class and have it serialized" << endl
<< " - use it to read and write matrices." << endl << endl;
}
class MyData
{
public:
MyData() : A(0), X(0), id()
{}
explicit MyData(int) : A(97), X(CV_PI), id("mydata1234") // explicit to avoid implicit conversion
{}
void write(FileStorage& fs) const //Write serialization for this class
{
fs << "{" << "A" << A << "X" << X << "id" << id << "}";
}
void read(const FileNode& node) //Read serialization for this class
{
A = (int)node["A"];
X = (double)node["X"];
id = (string)node["id"];
}
public: // Data Members
int A;
double X;
string id;
};
//These write and read functions must be defined for the serialization in FileStorage to work
static void write(FileStorage& fs, const std::string&, const MyData& x)
{
x.write(fs);
}
static void read(const FileNode& node, MyData& x, const MyData& default_value = MyData()){
if(node.empty())
x = default_value;
else
x.read(node);
}
// This function will print our custom class to the console
static ostream& operator<<(ostream& out, const MyData& m)
{
out << "{ id = " << m.id << ", ";
out << "X = " << m.X << ", ";
out << "A = " << m.A << "}";
return out;
}
int main(int ac, char** av)
{
string filename;
if (ac != 2)
{
help(av);
filename = "outputfile.yml.gz";
}
else
filename = av[1];
{ //write
Mat R = Mat_<uchar>::eye(3, 3),
T = Mat_<double>::zeros(3, 1);
MyData m(1);
FileStorage fs(filename, FileStorage::WRITE);
// or:
// FileStorage fs;
// fs.open(filename, FileStorage::WRITE);
fs << "iterationNr" << 100;
fs << "strings" << "["; // text - string sequence
fs << "image1.jpg" << "Awesomeness" << "../data/baboon.jpg";
fs << "]"; // close sequence
fs << "Mapping"; // text - mapping
fs << "{" << "One" << 1;
fs << "Two" << 2 << "}";
fs << "R" << R; // cv::Mat
fs << "T" << T;
fs << "MyData" << m; // your own data structures
fs.release(); // explicit close
cout << "Write operation to file:" << filename << " completed successfully." << endl;
}
{//read
cout << endl << "Reading: " << endl;
FileStorage fs;
fs.open(filename, FileStorage::READ);
int itNr;
//fs["iterationNr"] >> itNr;
itNr = (int) fs["iterationNr"];
cout << itNr;
if (!fs.isOpened())
{
cerr << "Failed to open " << filename << endl;
help(av);
return 1;
}
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;
n = fs["Mapping"]; // Read mappings from a sequence
cout << "Two " << (int)(n["Two"]) << "; ";
cout << "One " << (int)(n["One"]) << endl << endl;
MyData m;
Mat R, T;
fs["R"] >> R; // Read cv::Mat
fs["T"] >> T;
fs["MyData"] >> m; // Read your own structure_
cout << endl
<< "R = " << R << endl;
cout << "T = " << T << endl << endl;
cout << "MyData = " << endl << m << endl << endl;
//Show default behavior for non existing nodes
cout << "Attempt to read NonExisting (should initialize the data structure with its default).";
fs["NonExisting"] >> m;
cout << endl << "NonExisting = " << endl << m << endl;
}
cout << endl
<< "Tip: Open up " << filename << " with a text editor to see the serialized data." << endl;
return 0;
}
cv::FileNodeIterator
used to iterate through sequences and mappings.
Definition persistence.hpp:595
cv::FileNode
File Storage Node class.
Definition persistence.hpp:441
cv::FileNode::begin
FileNodeIterator begin() const
returns iterator pointing to the first node element
cv::FileNode::end
FileNodeIterator end() const
returns iterator pointing to the element following the last node element
cv::FileNode::empty
bool empty() const
returns true if the node is empty
cv::FileNode::type
int type() const
Returns type of the node.
cv::FileStorage
XML/YAML/JSON file storage class that encapsulates all the information necessary for writing or readi...
Definition persistence.hpp:261
cv::FileStorage::open
virtual bool open(const String &filename, int flags, const String &encoding=String())
Opens a file.
cv::FileStorage::isOpened
virtual bool isOpened() const
Checks whether the file is opened.
cv::FileStorage::release
virtual void release()
Closes the file and releases all the memory buffers.
cv::Mat_
Template matrix class derived from Mat.
Definition mat.hpp:2518
cv::Mat
n-dimensional dense array class
Definition mat.hpp:951
cv::operator<<
std::ostream & operator<<(std::ostream &, const DualQuat< _Tp > &)
CV_PI
#define CV_PI
Definition cvdef.h:382
main
int main(int argc, char *argv[])
Definition highgui_qt.cpp:3
core.hpp
cv
Definition core.hpp:107
cv::write
void write(FileStorage &fs, const String &name, int value)
cv::read
void read(const FileNode &node, int &value, int default_value)
std
STL namespace.