#pragma optimize( "", off|on ) Does Not Affect P-Code

The information in this article applies to:

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

      - Microsoft C/C++ for MS-DOS, version 7.0
      - Microsoft Visual C++ for Windows, versions 1.0 and 1.5
  

SUMMARY

Microsoft C/C++ compilers do not turn p-code optimizations on or off by using the #pragma optimize preprocessor directive if the string passed into the pragma is an empty string. The pragma optimize does work as expected if the string contains a "q".

MORE INFORMATION

This is expected behavior. The /Oq compiler option switch actually specifies more than an optimization--it is a compiler mode change. For this reason it must be explicitly listed in the #pragma optimize directive for it to be affected. The following is an example of turning off all optimizations and restoring default optimizations, including p-code:

   #pragma optimize("", off)
   #pragma optimize("q", off)

   #pragma optimize("", on)
   #pragma optimize("q", on)

Note that the optimize with p-code option (/Oq) must be specified on the command line in order to use the optimize pragma with "q".

Sample Code

/* Compile options needed: /Oq /Fc
*/

#include <stdio.h>

void HamAndEggs( void );

// The following directive should turn off p-code generation.

void main( )

   printf( "This function is using p-code\n" );
   HamAndEggs( );

// The following line turns p-code generation off.

// The following line should turn p-code generation on.

void HamAndEggs( )

    printf( "This function is not using p-code\n" );