Debug Assertion Faliure PLEASE HELP!

I''m creating a program based on some code from Tricks of the Windows Game Programming Grurus and am having a strange problem with the load bitmap code. Here is the code:

#define WIN32_LEAN_AND_MEAN  // just say no to MFC

#include    // include important windows stuff
#include  
#include 
#include  // include important C/C++ stuff
#include 
#include 
#include 
#include 
#include 
#include 
#include  
#include 
#include 
#include 

#define BITMAP_ID            0x4D42 // universal id for a bitmap
#define MAX_COLORS_PALETTE   256

// container structure for bitmaps .BMP file
typedef struct BITMAP_FILE_TAG
        {
        BITMAPFILEHEADER bitmapfileheader;  // this contains the bitmapfile header
        BITMAPINFOHEADER bitmapinfoheader;  // this is all the info including the palette
        PALETTEENTRY     palette[256];      // we will store the palette here
        UCHAR            *buffer;           // this is a pointer to the data

        } BITMAP_FILE, *BITMAP_FILE_PTR;
int Unload_Bitmap_File(BITMAP_FILE_PTR bitmap);
int Load_Bitmap_File(BITMAP_FILE_PTR bitmap, char *filename);

void main()
	{
		BITMAP_FILE icon;
Load_Bitmap_File(&icon, "smile2.bmp");
	Unload_Bitmap_File(&icon);
	}

int Unload_Bitmap_File(BITMAP_FILE_PTR bitmap)
{
// this function releases all memory associated with "bitmap"
if (bitmap->buffer)
   {
   // release memory
   free(bitmap->buffer);

   // reset pointer
   bitmap->buffer = NULL;

   } // end if

// return success
return(1);

} // end Unload_Bitmap_File

int Flip_Bitmap(UCHAR *image, int bytes_per_line, int height)
{
// this function is used to flip bottom-up .BMP images

UCHAR *buffer; // used to perform the image processing
int index;     // looping index

// allocate the temporary buffer
if (!(buffer = (UCHAR *)malloc(bytes_per_line*height)))
   return(0);

// copy image to work area
memcpy(buffer,image,bytes_per_line*height);

// flip vertically
for (index=0; index < height; index++)
    memcpy(ℑ[((height-1) - index)*bytes_per_line],
           &buffer[index*bytes_per_line], bytes_per_line);

// release the memory
free(buffer);

// return success
return(1);

} // end Flip_Bitmap

int Load_Bitmap_File(BITMAP_FILE_PTR bitmap, char *filename)
{
// this function opens a bitmap file and loads the data into bitmap

int file_handle,  // the file handle
    index;        // looping index

UCHAR   *temp_buffer = NULL; // used to convert 24 bit images to 16 bit
OFSTRUCT file_data;          // the file data information

// open the file if it exists
if ((file_handle = OpenFile(filename,&file_data,OF_READ))==-1)
   return(0);

// now load the bitmap file header
_lread(file_handle, &bitmap->bitmapfileheader,sizeof(BITMAPFILEHEADER));

// test if this is a bitmap file
if (bitmap->bitmapfileheader.bfType!=BITMAP_ID)
   {
   // close the file
   _lclose(file_handle);

   // return error
   return(0);
   } // end if

// now we know this is a bitmap, so read in all the sections

// first the bitmap infoheader

// now load the bitmap file header
_lread(file_handle, &bitmap->bitmapinfoheader,sizeof(BITMAPINFOHEADER));

// now load the color palette if there is one
if (bitmap->bitmapinfoheader.biBitCount == 8)
   {
   _lread(file_handle, &bitmap->palette,MAX_COLORS_PALETTE*sizeof(PALETTEENTRY));

   // now set all the flags in the palette correctly and fix the reversed 
   // BGR RGBQUAD data format
   for (index=0; index < MAX_COLORS_PALETTE; index++)
       {
       // reverse the red and green fields
       int temp_color                = bitmap->palette[index].peRed;
       bitmap->palette[index].peRed  = bitmap->palette[index].peBlue;
       bitmap->palette[index].peBlue = temp_color;
       
       // always set the flags word to this
       bitmap->palette[index].peFlags = PC_NOCOLLAPSE;
       } // end for index

    } // end if

// finally the image data itself
_lseek(file_handle,-(int)(bitmap->bitmapinfoheader.biSizeImage),SEEK_END);

// now read in the image, if the image is 8 or 16 bit then simply read it
// but if its 24 bit then read it into a temporary area and then convert
// it to a 16 bit image

if (bitmap->bitmapinfoheader.biBitCount==8 // bitmap->bitmapinfoheader.biBitCount==16 // 
    bitmap->bitmapinfoheader.biBitCount==24)
   {
   // delete the last image if there was one
   if (bitmap->buffer)
       free(bitmap->buffer);

   // allocate the memory for the image
   if (!(bitmap->buffer = (UCHAR *)malloc(bitmap->bitmapinfoheader.biSizeImage)))
      {
      // close the file
      _lclose(file_handle);

      // return error
      return(0);
      } // end if

   // now read it in
   _lread(file_handle,bitmap->buffer,bitmap->bitmapinfoheader.biSizeImage);

   } // end if
else
   {
   // serious problem
   return(0);

   } // end else

#if 0
// write the file info out 
printf("\nfilename:%s \nsize=%d \nwidth=%d \nheight=%d \nbitsperpixel=%d \ncolors=%d \nimpcolors=%d",
        filename,
        bitmap->bitmapinfoheader.biSizeImage,
        bitmap->bitmapinfoheader.biWidth,
        bitmap->bitmapinfoheader.biHeight,
		bitmap->bitmapinfoheader.biBitCount,
        bitmap->bitmapinfoheader.biClrUsed,
        bitmap->bitmapinfoheader.biClrImportant);
#endif

// close the file
_lclose(file_handle);

// flip the bitmap
Flip_Bitmap(bitmap->buffer, 
            bitmap->bitmapinfoheader.biWidth*(bitmap->bitmapinfoheader.biBitCount/8), 
            bitmap->bitmapinfoheader.biHeight);

// return success
return(1);

} // end Load_Bitmap_File

Whenever I call the Load_Bitmap_File function with a global BITMAP_FILE variable, it works fine. But when I call it with a local variable as in the above code, it brings up a dialog box with "Debug Assertion Failed!" in it. Any suggestions? (BTW, this is NOT a DOS game, I just put it in a DOS shell to simplify the debugging of it.)

Why do you think running in DOS mode is easier to debug? The VC++ debugger is really easy to use. It would tell you exactly where your program is asserting.

My guess would be this:

if (bitmap->buffer)
free(bitmap->buffer);

The program will assert if you call free on an invalid pointer, and checking to see if the pointer is NULL is not always a sure-fire way to tell if it is valid unless you explicitly zero-out your BITMAP_FILE struct after you declare it. The reason it might work if you use a global struct is because I believe global structs do get zeroed-out automatically. It think it is all compiler-specific though so you really should always zero it yourself to be sure. So in main() try adding "icon.buffer = NULL;" before calling Load_Bitmap_File().

Topic Locked