DOC: assert() Macro Does Not Display Pop-Up Window in Win32

• The C Run-time (CRT) included with: - Microsoft Visual C++ 32-bit Edition, version 1.0

SUMMARY

The documentation in the Microsoft C "Run-Time Library Reference" for the assert macro states that in Windows an assertion failure causes a pop-up box to be displayed. This is stated similarly in the online help. Although this is true for 16-bit Windows applications, under Win32 the macro just causes the application to abort; no pop-up window is displayed.

The Visual C++ 2.0 documentation has the correct information.

MORE INFORMATION

The C run-time assert() macro was originally designed to display its diagnostic message using console output. In the 16-bit Windows version of the C run time, the macro was modified to use the Windows Graphical User Interface (GUI) application programming interface (API). This was necessary because 16-bit Windows does not support a console API.

Unlike 16-bit Windows, however, Win32 has both a GUI and console API set, and therefore the assert() macro returns to its original form as a console output macro.

It is possible to create a user-defined version of the assert() macro that displays its diagnostic message in a pop-up window. The sample code provided below shows one way of doing this:

Sample Code

   /* Compile options needed: none
   */

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

   // Prototype for the function called by the assert macro.
   void  ShowAssertion(void * expr, void * filename, unsigned lineno);

   // The following should all be on one line. It wraps around because
   // of its length.
   #define assert(exp) (void)( (exp) || (ShowAssertion(#exp, __FILE__,
   __LINE__), 0) )

   static char AssertString[] = "Expression %s, File %s, Line %d\n";

   void  ShowAssertion(void * expr, void * filename, unsigned lineno)
   {
       char buffer[256];

       sprintf( buffer, AssertString, expr, filename, lineno );
       MessageBox( NULL, buffer, "ASSERTION FAILED",
                   MB_OK | MB_ICONHAND | MB_TASKMODAL );

       abort();
   }