Thread: Possible Memory Leak?

Im having trouble finding what I belive may be a memory leak. The function Im working with seems to work fine for several calls then it crashes. Each time I call the function, the memory used by the program increases until the function crashes, the whole program does not crash, just the function. Im still very new to C programming and this is my first attempt to work with screen capture any advice on what Im doing wrong would be great... here is the function thats giving me so much trouble.

Code:

int grab_screen( int client_fd, char buf[3][2048] )///////////////////////////////////////////////////////////////////////////////
{
   // FILE *f         = NULL;
    HDC hsDC        = NULL;
    HDC hdDC        = NULL;
    HBITMAP hBMP    = NULL;
    BITMAPINFO BI;

    png_struct *pstr;
    png_info *pinf;
    int width, height;
    int i, j, k, u, v;
    int retval, icon;

    icon = atoi( buf[1] + 8 );

    WaitForSingleObject( shot.sem, INFINITE );

   /* initial data setup */

    if( ( hsDC = GetDC( NULL ) ) == NULL )
        return( ERR_GDI_FAILED );

    width  = GetDeviceCaps( hsDC, HORZRES );
    height = GetDeviceCaps( hsDC, VERTRES );

    if( shot.width  != width  ||
        shot.height != height )
    {
        if( shot.bytes_tn != NULL ) free( shot.bytes_tn );
        if( shot.bytes_fs != NULL ) free( shot.bytes_fs );
        if( shot.rows_tn  != NULL ) free( shot.rows_tn  );
        if( shot.rows_fs  != NULL ) free( shot.rows_fs  );

        retval = ERR_MALLOC_FAILED;

        if( ( shot.bytes_tn = malloc( (
                width * height * 3 ) / 16 ) ) == NULL )
            goto png_exit;

        if( ( shot.bytes_fs = malloc(
                width * height * 3 ) ) == NULL )
            goto png_exit;

        if( ( shot.rows_tn = malloc( (
                height * sizeof( unsigned char* ) ) / 4 ) ) == NULL )
            goto png_exit;
    
        if( ( shot.rows_fs = malloc(
                height * sizeof( unsigned char* ) ) ) == NULL )
            goto png_exit;
    
        shot.width  = width;
        shot.height = height;



    }

    /* create the destination DC & bitmap */

    retval = ERR_GDI_FAILED;

    hBMP = CreateCompatibleBitmap( hsDC, shot.width, shot.height );

    if( hBMP == NULL )
        goto png_exit;

    if( ( hdDC = CreateCompatibleDC( hsDC ) ) == NULL )
        goto png_exit;

    /* copy desktop pixels into bitmap, get the bits */

    memset( &BI, 0, sizeof( BI ) );

    BI.bmiHeader.biSize     = sizeof( BI.bmiHeader );
    BI.bmiHeader.biWidth    = shot.width;
    BI.bmiHeader.biHeight   = shot.height;
    BI.bmiHeader.biPlanes   = 1;
    BI.bmiHeader.biBitCount = 24;

    if( SelectObject( hdDC, hBMP ) == NULL )
        goto png_exit;

    if( BitBlt( hdDC, 0, 0, shot.width, shot.height,
                hsDC, 0, 0, SRCCOPY ) == 0 )
        goto png_exit;

    if( GetDIBits( hdDC, hBMP, 0, shot.height, shot.bytes_fs,
                   &BI, DIB_RGB_COLORS ) != shot.height )
        goto png_exit;


    /* setup the png data row pointers */

    if( icon )
    {
        int B, G, R;
        width  /= 4;
        height /= 4;

       // shrink the image to 25% of its size 

        for( j = 0, k = height - 1; j < height; j++, k-- )
        {
            for( i = 0; i < width * 3; i +=3 )
            {
                B = G = R = 0;

                for( v = j * 4; v < (j + 1) * 4; v++ )
                {
                    for( u = i * 4; u < (i + 3) * 4; u += 3 )
                    {
                        B += shot.bytes_fs[    u + v * shot.width * 3];
                        G += shot.bytes_fs[1 + u + v * shot.width * 3];
                        R += shot.bytes_fs[2 + u + v * shot.width * 3];
                    }
                }

                shot.bytes_tn[    i + j * width * 3] = B / 16;
                shot.bytes_tn[1 + i + j * width * 3] = G / 16;
                shot.bytes_tn[2 + i + j * width * 3] = R / 16;
             }

	    shot.rows_tn[j] = shot.bytes_tn + k * width * 3;
        }

    }
    else
        for( j = 0, k = height - 1; j < height; j++, k-- )
	    shot.rows_fs[j] = shot.bytes_fs + k * width * 3;

    /* finally write the png */

    if( send( client_fd, "HTTP/1.0 200 OK\r\nContent-Type: "
                         "image/png\r\n\r\n", 44, 0 ) != 44 )
        return( ERR_SEND_FAILED );

    pstr = png_create_write_struct( PNG_LIBPNG_VER_STRING, 0, 0, 0 );
    pinf = png_create_info_struct( pstr );

    png_set_IHDR( pstr, pinf, width, height, 8,
                  PNG_COLOR_TYPE_RGB, 
                  PNG_INTERLACE_NONE,
                  PNG_COMPRESSION_TYPE_BASE,
                  PNG_FILTER_TYPE_BASE );

    png_set_bgr( pstr );

    png_set_write_fn( pstr, (void *) client_fd,
                      user_write_data, user_flush_data );

    png_write_info( pstr, pinf );
    png_write_image( pstr, ( icon ) ? shot.rows_tn : shot.rows_fs );
    png_write_end( pstr, pinf );
    png_destroy_write_struct( &pstr, &pinf );

    retval = 0;
	        

png_exit:

    if( hsDC != NULL );
        ReleaseDC( NULL, hsDC );
    
    if( hdDC != NULL );
        ReleaseDC( NULL, hdDC );

    if( hBMP != NULL )
        DeleteObject( hBMP ); 

    ReleaseSemaphore( shot.sem, 1, NULL );

    return( retval );
}

Originally Posted by g1i7ch

the whole program does not crash, just the function.

Very odd thing to say. What does it mean? How can "just the function" crash? I think you're using some new-fangled definition of "crash".

The best way to fix that would be to set them all to NULL after freeing them, or just free them just before the malloc() calls.

Tried both suggestions and still no luck.
Debugger gives only one hintThe thread has exited with code 10 (0xA).)
but I couldnt find any helpful info on it...I am sure this function is where the problem is, maybe a buf overflow somewhere...Im just not seeing it.
thanks for all the help dwks

Yes, this must be the trouble...is there a better way to shrink the image, this is ugly code.
many thanks dwks

Ok, here are the details.

Each time I call grab_screen I lose 5M of memory which just happens to be about the amount needed to store the bitmap image of my screen...but its not being freed. Make 5 calls lose 25M of memory.

After 10-15 calls on grab_screen the function returns a blank image. Once the function starts returning a blank image the program quits eating up the memory and continues to function correctly minus the grab_screen part.

I really appreciate all help...I sure this is something stupidly simple I missed somewhere and am just not seeing/getting.

ALLRIGHT! As I thought about my reply to Salems post I looked at my cleanup I left out one important thing...

DeleteDC(hdDC );

Im sure this is something stupidly simple I missed somewhere and am just not seeing/getting.

I knew it.
Thank you all for the help All is well now.