BUG: ExtractIcon Not Freeing Up Memory

• Microsoft Windows Software Development Kit (SDK) for Windows version 3.1

SYMPTOMS

Calling ExtractIcon() with a -1 as the iIcon parameter to obtain the total number of icons in a file results in a loss of system resources. Each time an application calls ExtractIcon() in this manner, the system loses some resources. However, when the application that called ExtractIcon() terminates, the resources are freed. This situation can cause low memory conditions when an application that is running calls ExtractIcon() many times to find the number of icons in a number of different files.

CAUSE

The problem occurs when you call ExtractIcon() with the iIcon parameter set to -1 in order to count the number of icons. ExtractIcon() erroneously omits a GlobalFree call that is supposed to free some intermediate global memory used to count the number of icons in the specified file. As a result, each call made to ExtractIcon() in this manner results in a loss of memory and an occupied selector until the application terminates.

RESOLUTION

To work around the problem, you can extract consecutive icons in a file until ExtractIcon() fails. This will give you the total number of icons in the file without memory loss.

STATUS

Microsoft has confirmed this to be a bug in the products listed at the beginning of this article. We are researching this bug and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

Below is a function that you could call to retrieve the number of icons in a file:

int NumIcons(HINSTANCE hinst, LPCSTR lpszExeName)
   {
   int i = 0;
   HICON hIcon;

   while (hIcon = ExtractIcon(hinst,lpszExeName,i))
     {
     i++;
     DestroyIcon(hIcon);
     }
   return (i);
   }