Cleaning up resources

During termination-handler execution, you may not know which resources have been acquired before the termination handler was called. It's possible that the __try statement block was interrupted before all resources were acquired, so that not all resources were opened.

To be safe, you should check to see which resources are open before proceeding with termination-handling cleanup. A recommended procedure is to:

1. Initialize handles to NULL.

2. In the __try statement block, acquire resources. Handles are set to positive values as the resource is acquired.

3. In the __finally statement block, release each resource whose corresponding handle or flag variable is nonzero or not NULL.

Example

For example, the following code uses a termination handler to close three files and release a memory block. These resources were acquired in the __try statement block. Before cleaning up a resource, the code first checks to see if the resource was acquired.

// exceptions_Cleaning_up_Resources.cpp
#include <stdlib.h>
#include <malloc.h>
#include <stdio.h>
#include <windows.h>

void fileOps() {
   FILE  *fp1 = NULL,
         *fp2 = NULL,
         *fp3 = NULL;
   LPVOID lpvoid = NULL;
   errno_t err;

   __try {
      lpvoid = malloc( BUFSIZ );

      err = fopen_s(&fp1, "ADDRESS.DAT", "w+" );
      err = fopen_s(&fp2, "NAMES.DAT", "w+" );
      err = fopen_s(&fp3, "CARS.DAT", "w+" );
   }
   __finally {
      if ( fp1 )
         fclose( fp1 );
      if ( fp2 )
         fclose( fp2 );
      if ( fp3 )
         fclose( fp3 );
      if ( lpvoid )
         free( lpvoid );
   }
}

int main() {
   fileOps();
}

See also

Writing a termination handler
Structured Exception Handling (C/C++)