DOCUMENT:Q111753  26-JUL-2001  [visualc]
TITLE   :DOC: assert() Macro Does Not Display Pop-Up Window in Win32
PRODUCT :Microsoft C Compiler
PROD/VER:winnt:
OPER/SYS:
KEYWORDS:kbdocfix kbdocerr kbCRT kbVC

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The information in this article applies to:

 - The C Run-Time (CRT), included with:
    - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, version 1.0 
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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();
      }

Additional query words: 2.00 debug runtime run time

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Keywords          : kbdocfix kbdocerr kbCRT kbVC 
Technology        : kbVCsearch kbAudDeveloper kbCRT
Version           : winnt:

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