Exporting Data in Binary Format

[emaghero]

Greetings one and all,

I wish to output data to a file in binary format. The data will take the form of a 2-D array of doubles. Calculated in C++. It (the file) will be used in conjunction with a program which does contour plots.

I have an inkling that this can be done in Microsoft Visual Studio using the fstream class and the insertion operator, as you would for a normal txt file.

Can anybody help me out or poitn me in the right direction?

[horace1]

have a look at binary files in this tutorial
http://www.cplusplus.com/doc/tutorial/files.html
http://www.cprogramming.com/tutorial/lesson10.html

[emaghero]

The following code tells you how to create a binary file in C++. Also give is an example of how to export to a binary file.

The argument that can be given to a fstream object ios_base::binary is strictly speaking not a binary file. Check it with a Hex Editor and you'll see it's still in txt format.

The following section of code works in Microsoft Visual Studio, but as far as I'm aware is not Microsift specific.

 
#include <iostream>
#include <tchar.h>
#include <cstring>
#include <cstdlib>
#include <cmath>
//The following headers are required for binary files
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <io.h>
#include <stdio.h>
 
 
 
using namespace std;
 
int _tmain(int argc, _TCHAR* argv[]){
 
    int bytes;//This is a variable that contains the data that is being sent to the binary file
 
    int file=_open("c:\\Modes.pm",_O_BINARY|_O_WRONLY|_O_CREAT,_S_IREAD|_S_IWRITE);//Command to open a binary file for reading and writing
 
    if(file==-1){
        perror("Failed to open file");//Error message in case the file is not created
    }
    else{
        cout<<"file is open\n";
    }
 
    char *header="Robert's File Format";//Create a pointer to a header
 
    bytes=_write(file,header,(unsigned int)(strlen(header)));//This writes the header to the binary file
 
    int revision=1;//Revision number for the file format
 
    bytes=_write(file,(void *)&revision,sizeof(int));//This sends the revision number to the binary file
 
    int num_modes=3;//This tells the user how many modes are inside the binary file
 
    bytes=_write(file,(void *)&num_modes,sizeof(int));//This sends the number of modes to the binary file
 
    //Does the void pointer mean that it doesn't matter what type of data you're 
    //sending to the file as long as the size is correct? It does matter what the type is.
 
    int row = 6;//The number of rows that the array will have
    double col = 5;//The number of columns that the array will have
 
    //Send this data to the binary file
    bytes=_write(file,(void *)&row,sizeof(int));
    bytes=_write(file,(void *)&col,sizeof(int));
 
    //Doubles can also be sent to the binary files
    double d;
    //Set up a loop over the modes
    for(int k=0;k<num_modes;k++){
        for(int i=0;i<row;i++){
            for(int j=0;j<col;j++){
                     d=cos((double)(j))*cos((double)(j))*sin((double)(i))*sin((double)(i));
                bytes=_write(file,(void *)&d,sizeof(double));
            }
        }
    }
    cout<<"Data successfully exported\n";
    _close(file);//Close the file when you are finished operating with it
 
    system("PAUSE");
    return 0;
}
 
 

There is a Microsoft specific class that enables the user to to use the insertion operator to write to a binary file. However, since I want my code to be platform independent I have not learned much about it.