Different Warnings Appear Using Different Optimizations

                       |            |                     | 4.00
MS-DOS                 | OS/2       | WINDOWS             | WINDOWS NT

The information in this article applies to:

• The Microsoft C/C++ Compiler (CL.EXE), included with:

      - Microsoft C for MS-DOS, versions 6.0, 6.0a, and 6.0ax
      - Microsoft C for OS/2, versions 6.0 and 6.0a
      - Microsoft C/C++ for MS-DOS, versions 7.0
      - Microsoft Visual C++ for Windows, version 1.0, 1.5, 1.51, and
        1.52
      - Microsoft Visual C++, 32-bit Edition, version 1.0, 2.0, 2.1, and
        4.0
  

The information in this article is included in the documentation starting with Visual C++ 5.0. Look there for future revisions.

SUMMARY

In Microsoft C/C++ compiler, different warning messages can appear during separate compilations of the same code when different optimizations are used. This is normal behavior that occurs because some warnings are found only while optimizing.

MORE INFORMATION

If the sample code below is compiled with /W4 (all warnings) and the /Os optimization (optimize for space), no warnings are found. However, when the code is compiled with /W4 and /Osle (optimize for size, loop, and global-register allocation), the following warning is generated:

   file.c(7) : warning C4202: unreachable code

   file.c(7) : warning C4702: unreachable code

Sample Code

  #include <stdio.h>

  void main(void)
  {
       goto bottom;

       printf("Not used\n");    /* Code that is not used */

  }