C&C++&opencv文件操作

1. C

头文件：stdio.h
相关函数：

 1. fopen()
 2. fclose()
 3. fgetc(FILE *fp)
 4. fputc(int ch,FILE *fp)
 5. fgets(char *str, int n, FILE *fp)
 6. fputs()
 7. fprintf(FILE *fp,char *format,arg_list)
 8. fread(void *buffer,unsigned sife,unsigned count,FILE *fp)
 9. fwrite(void *buffer,unsigned sife,unsigned count,FILE *fp)
 10. getw(FILE *fp)
 11. putw(int n,FILE *fp)
 12. feof(FILE *fp)
 13. ferror(FILE *fp)
 14. clearerr(FILE *fp)
 15. fseek(FILE *fp,long offset,int base)
 16. 

文件打开方式：

例子：将一个文件的内容复制到另一个文件中去。

#include <stdio.h>  
void main(int argc,char *argv[]) //命令行参数  
{  
   int ch;  
    FILE *in,*out; //定义in和out两个文件类型指针  
    if(argc!=3) //判断命令行是否正确  
    {  

        printf("Error in format,Usage: copyfile filename1 filename2
");  
        return; //命令行错，结束程序的执行  

    }  
   //按读方式打开由argv[1]指出的文件  
    if((in=fopen(argv[1],"r"))==NULL)  

    {  
        printf("The file <%s> can not be opened.
",argv[1]);  
        return; //打开失败，结束程序的执行  

    }  
    //成功打开了argv[1]所指文件，再  
    //按写方式打开由argv[2]指出的文件  
    if((out=fopen(argv[2],"w"))==NULL)  
    {  
        printf("The file %s can not be opened.
",argv[2]);  
        return; //打开失败，结束程序的执行  
    }  
    //成功打开了argv[2]所指文件  
    ch=fgetc(in); //从in所指文件的当前指针位置读取一个字符  
    while(ch!=EOF) //判断刚读取的字符是否是文件结束符  
    { 
        fputc(ch,out); //若不是结束符，将它写入out所指文件  
        ch=fgetc(in); //继续从in所指文件中读取下一个字符  
    } //完成将in所指文件的内容写入（复制）到out所指文件中  
    fclose(in); //关闭in所指文件  
    fclose(out); //关闭out所指文件  
}  

将一个文件的内容附加到另一个文件中去。

#include <stdio.h>  
#define SIZE 512  
void main(int argc,char *argv[])  
{  
    char buffer[SIZE];  
    FILE *fp1,*fp2;  
    if(argc!=3)  
   {  
        printf("Usage: linkfile filename1 filename2
");  
        return;  
    }  
    // 按追加方式打开argv[1] 所指文件  
    if((fp1=fopen(argv[1],"a"))==NULL)  
    {  
        printf("The file %s can not be opened.
",argv[1]);  
        return;  
    }  
    if((fp2=fopen(argv[2],"r"))==NULL)  
    {  
        printf("The file %s can not be opened.
",argv[2]);  
        return;  
    }  
    // 读入一行立即写出，直到文件结束  
    while(fgets(buffer,SIZE,fp1)!=NULL)  
        printf("%s
",buffer);  
    while(fgets(buffer,SIZE,fp2)!=NULL)  
        fputs(buffer,fp1);  
    fclose(fp1);  
    fclose(fp2);  
    if((fp1=fopen(argv[1],"r"))==NULL)  
    {  
        printf("The file %s can not be opened.
",argv[1]);  
        return;  
    }  
    while(fgets(buffer,SIZE,fp1)!=NULL)  
        printf("%s
",buffer);  
    fclose(fp1);  
}  

博客参考：

2. C++

头文件：fstream
cstdlib
相关函数：

 1. ofstream
 2. ifstream
 3. fstream
 4. open()
 5. istream &seekg(streamoff offset,seek_dir origin);
    ostream &seekp(streamoff offset,seek_dir origin);
 6. close()
 7. ios::app： 以追加的方式打开文件
ios::ate： 文件打开后定位到文件尾，ios:app就包含有此属性
ios::binary： 以二进制方式打开文件，缺省的方式是文本方式。两种方式的区别见前文
ios::in： 文件以输入方式打开
ios::out： 文件以输出方式打开
ios::nocreate： 不建立文件，所以文件不存在时打开失败
ios::noreplace：不覆盖文件，所以打开文件时如果文件存在失败
ios::trunc： 如果文件存在，把文件长度设为0

例子：读取文件内容

#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;
int main ()
{
    char buffer[256];
    ifstream examplefile("example.txt");
    if (! examplefile.is_open())
    {
       cout << "Error opening file"; exit (1);
    }
    while (!examplefile.eof())
    {
        examplefile.getline(buffer,100);
        cout<<buffer<< endl;
    }
    return 0;
}

获取二进制文件大小：

#include <iostream>
#include <fstream>
using namespace std;
int main ()
{
   const char * filename = "example.txt";
    long l,m;
    ifstream file(filename, ios::in|ios::binary);
    l = file.tellg();
    file.seekg(0, ios::end);
    m = file.tellg();
    file.close();
    cout <<"size of "<< filename;
    cout <<" is "<< (m-l)<<" bytes.
";
    return 0;
}

文件定位：

file1.seekg(1234,ios::cur);//把文件的读指针从当前位置向后移1234个字节
file2.seekp(1234,ios::beg);//把文件的写指针从文件开头向后移1234个字节

博客参考：

3. OPENCV

文件打开格式要求：.yml/.yaml/.xml
操作例子

// file write
#include "opencv2/opencv.hpp"
#include <time.h>

using namespace cv;
using namespace std;

int main(int, char** argv)
{
    FileStorage fs("test.yml", FileStorage::WRITE);

    fs << "frameCount" << 5;
    time_t rawtime; time(&rawtime);
    fs << "calibrationDate" << asctime(localtime(&rawtime));
    Mat cameraMatrix = (Mat_<double>(3,3) << 1000, 0, 320, 0, 1000, 240, 0, 0, 1);
    Mat distCoeffs = (Mat_<double>(5,1) << 0.1, 0.01, -0.001, 0, 0);
    fs << "cameraMatrix" << cameraMatrix << "distCoeffs" << distCoeffs;
    fs << "features" << "[";
    for( int i = 0; i < 3; i++ )
    {
        int x = rand() % 640;
        int y = rand() % 480;
        uchar lbp = rand() % 256;

        fs << "{:" << "x" << x << "y" << y << "lbp" << "[:";
        for( int j = 0; j < 8; j++ )
            fs << ((lbp >> j) & 1);
        fs << "]" << "}";
    }
    fs << "]";
    fs.release();
    return 0;
}

文件读取：

// file read
FileStorage fs2("test.yml", FileStorage::READ);

// first method: use (type) operator on FileNode.
int frameCount = (int)fs2["frameCount"];

std::string date;
// second method: use FileNode::operator >>
fs2["calibrationDate"] >> date;

Mat cameraMatrix2, distCoeffs2;
fs2["cameraMatrix"] >> cameraMatrix2;
fs2["distCoeffs"] >> distCoeffs2;

cout << "frameCount: " << frameCount << endl
     << "calibration date: " << date << endl
     << "camera matrix: " << cameraMatrix2 << endl
     << "distortion coeffs: " << distCoeffs2 << endl;

FileNode features = fs2["features"];
FileNodeIterator it = features.begin(), it_end = features.end();
int idx = 0;
std::vector<uchar> lbpval;

// iterate through a sequence using FileNodeIterator
for( ; it != it_end; ++it, idx++ )
{
    cout << "feature #" << idx << ": ";
    cout << "x=" << (int)(*it)["x"] << ", y=" << (int)(*it)["y"] << ", lbp: (";
    // you can also easily read numerical arrays using FileNode >> std::vector operator.
    (*it)["lbp"] >> lbpval;
    for( int i = 0; i < (int)lbpval.size(); i++ )
        cout << " " << (int)lbpval[i];
    cout << ")" << endl;
}
fs.release();

博客参考：