Loading error

[ozone95]

I'm relatively new to c++.
I use the DEV-c++ compiler,and for a while I've been trying to print bitmaps on the screen. But when I use the LoadBMP() function I get an error not from my compiler, but from my desktop asking me if I want to send this error to windows(which i never do). Can anyone help me troubleshoot this or find a better way to print bitmaps.?

[Duthomhas]

It probably means you've got a dangling pointer in there somewhere.

Post the offending code.

[ozone95]

here:[code]

#include"load.h"
#include<windows.h>

main()
{
LoadBMP("rec/_rangertst_.bmp",0);

while (1==1);//this keeps the program from shutting off instantly
return 0;
}
[code/]

this is the "load.h" i found

[code]

#include <conio.h>
#include <stdio.h>
#include <stdlib.h>


bool LoadBMP(char *sBMPFile,unsigned char* buffer)
{
FILE *fp;
char buf[0x36];
int i,j;
int ch;

fp=fopen(sBMPFile,"rb");
if( fp != NULL ) {
if (fread(buf,0x36, 1, fp ) !=0) {
for(i=0,j=0;i<256*256;i++,j+=3) {
buffer[j+2]=(unsigned char)fgetc(fp);
buffer[j+1]=(unsigned char)fgetc(fp);
buffer[j] =(unsigned char)fgetc(fp);
}
}
fclose( fp );
} else printf("file not found\n");

return true;
}
[code\]

when the file's not found it works perfectly

[Duthomhas]

You are trying to write to memory you don't own. Try

#include <stdio.h>
#include <windows.h>

#include "load.h"

int main()
{
  unsigned char *p;
  int x, y;

  // pixels represents the bits of the image.
  // I assume an image sized 256 by 256 pixels (because that is
  // what the LoadBMP() function assumes).
  // The function loads pixels as triplets ordered as R,G,B.
  unsigned char *pixels = (unsigned char*)malloc( 256 * 256 * 3 );

  // Fill the pixels buffer from the file
  LoadBMP( "test256x256.bmp", pixels );

  // Draw the image on the console window

  // first, find the console window
  SetConsoleTitle( "ozone95's bitmap" );
  HWND hConsole = FindWindow( NULL, "ozone95's bitmap" );
  HDC hConsoleDC = GetDC( hConsole );

  // then, loop through all the pixels and draw them
  p = pixels;
  for (y = 255; y >= 0; y--)
    for (x = 0; x < 256; x++)
    {
      SetPixel( hConsoleDC, x, y, RGB( p[0], p[1], p[2] ) );
      p += 3;
    }

  // finally, release the DC and free memory used
  ReleaseDC( hConsole, hConsoleDC );
  DeleteDC( hConsoleDC );
  free( pixels );

  // wait for the user to end
  getchar();
  return 0;
}

You'll have to fix that 'bool' and 'true' in "load.h" to 'int' and '1' respectively. When you compile you'll have to link against libgdi32:
gcc main.c -lgdi32

Make sure that your bitmap file is a 256 by 256 pixel, 24-bit, uncompressed, unflipped DIB, or you might see some weird stuff.

BTW, the LoadBMP() function should have its own .c file.

Hope this helps.

[ozone95]

Tks very much, I just have one more question how do you use
gcc main.c -lgdi32 to link libgdi32?

[Duthomhas]

Sorry I haven't looked in here for so long...

That command is if you are using the GCC at the command prompt. If you are using another C compiler change the name. For example, Borland would be:
bcc main.c -lgdi32

If you are using an IDE, you should have a menu option somewhere to specify which libraries you want to link with. Link with the gdi32 library.

Hope this helps.

[ozone95]

I am extreamly sorry for taking so long to tinker with this, but i've found how to link the library. It doesn't work just yet but i'm very close,tks!

[ropez]

If you want to upgrade your code from "C style", to "C++ style" here's a suggestion. I haven't tested if this works, because I don't have windows. You might have to fixe some errors, but you should get the idea.

#include "load.h"

#include <windows.h>

#include <iostream>
#include <fstream>
#include <cstdio>

const int W = 256;
const int H = 256;

bool LoadBMP(const char* sBMPFile, unsigned char* buffer)
{ 
    int i,j;
    
    std::ifstream file(sBMPFile, ios::in | ios::binary);
    if ( file ) {
        if (file.seekg(0x36)) {
            for (i=0,j=0; i < W*H; i++,j+=3) {
                buffer[j+2]=(unsigned char)file.get();
                buffer[j+1]=(unsigned char)file.get();
                buffer[j]  =(unsigned char)file.get();
            }
        }
    } else {
        std::cout << "file not found" << std::endl;
        return false;
    }
    return true;
}


int main()
{
    // pixels represents the bits of the image.
    // I assume an image sized 256 by 256 pixels (because that is
    // what the LoadBMP() function assumes).
    // The function loads pixels as triplets ordered as R,G,B.
    unsigned char* pixels = new unsigned char[W * H * 3];
    
    // Fill the pixels buffer from the file
    LoadBMP( "test256x256.bmp", pixels );
    
    // Draw the image on the console window
    
    // first, find the console window
    SetConsoleTitle( "ozone95's bitmap" );
    HWND hConsole = FindWindow( NULL, "ozone95's bitmap" );
    HDC hConsoleDC = GetDC( hConsole );
    
    // then, loop through all the pixels and draw them
    unsigned char* p = pixels;
    for (int y = H-1; y >= 0; y--) {
        for (int x = 0; x < W; x++) {
            SetPixel( hConsoleDC, x, y, RGB( p[0], p[1], p[2] ) );
            p += 3;
        }
    }
    
    // finally, release the DC and free memory used
    ReleaseDC( hConsole, hConsoleDC );
    DeleteDC( hConsoleDC );
    delete[] pixels;
    
    // wait for the user to end
    getchar();
    return 0;
}

Then save as main.cpp, and use g++ instead of gcc to compile.