Question

The example code I’ve seen for this seems to use standard C file output functions, but I’d like to make it in C++.

I tried using fsteam functions to do it, but no data is written to the .bmp file at all.

So far, I have tried the standard <<, put, and write, and none of these work. If I open it up with a hex editor, the file is still empty.

It’s odd, since the input functions work fine.

Here’s a piece of the code I used to test to see if it was working:

output.open("WHITE.bmp");
output.put('B'); // this doesn't seem to work, the file is empty when I open it in a hex editor. 
output.put('M');

And the rest of the code:

#include <iostream>
#include <fstream>

using namespace std;
typedef unsigned char  byte;
typedef unsigned short dbyte;

struct BMPINFO
{
    int width;
    int height;
};

int main()
{
    ifstream sourcefile;
    ofstream output;

    int threshold = 150;



    sourcefile.open("RED.bmp");


    if(sourcefile.fail())
    {
        cout << "Could not open RED.bmp" << endl;
        return 1;
    }


    if(sourcefile.get() == 'B')
    {
        if(sourcefile.get() == 'M')
        {
            cout << "RED.bmp is a valid .bmp file" << endl;
        }
    }

    else
    {
        cout << "RED.bmp is not a valid .bmp file" << endl;
        return 1;
    }

    BMPINFO image;

    // seeks to bitmap width, this file is little end in.

    sourcefile.seekg (0x12, ios::beg);

    unsigned int i = (unsigned)sourcefile.get(); 
    i += (unsigned)sourcefile.get() << 8;


    image.width = i;

    cout << "The width of the image is: " << image.width << endl;

    sourcefile.seekg (0x16, ios::beg);

    i = sourcefile.get(); 
    i += (unsigned)sourcefile.get() << 8;

    image.height = i;


    cout << "The height of the image is: " << image.height << endl;

    int loc_pixels;

    sourcefile.seekg (0x0A, ios::beg);

    loc_pixels = sourcefile.get();

    cout << "Location of pixel array is: " << loc_pixels << endl;


    output.open("WHITE.bmp");

    output.put('B'); // this doesn't seem to work, the file is empty when I open it in a hex editor. 
    output.put('M');

    if(output.bad())
    {
        cout << "the attempt to output didn't work" << endl;
        return 1;
    }


    sourcefile.seekg(loc_pixels, ios::beg);

    char data[30000];

    output.close();


    return 0;
}

Is there a special function I should be using to output to this .bmp file?

EDIT – added more code, though most of it doesn’t have to do with file output

Answer 1

You have a buffer overflow bug in this code:

char data[30000];    // Prepare file for usage -- just copy one thing from the file to the other
sourcefile.read(data, image.height * image.width );

You are reading in image.height*image.width bytes, and trying to fit them into 30000 bytes. You should structure your code so that those two numbers are related.

Try this:

std::vector<char> data(image.height * image.width);
sourcefile.read(&data[0], data.size());