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

ID: Q84477

7.00 | 1.00 1.50 MS-DOS | WINDOWS kbtool

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)

In the following sample code, the main function is compiled with p-code, and the function HamAndEggs is not. The #pragma optimize statements with empty strings have no effect. This can be verified by examining a mixed source-assembly listing.

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.

#pragma optimize( "", off )

void main( )

{

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

}

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

#pragma optimize ( "q", off )

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

#pragma optimize( "", on )

void HamAndEggs( )

{

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

}

Additional reference words: kbinf 7.00 1.00 1.50 8.00 8.00c pcode KBCategory: kbtool KBSubcategory: CLIss Keywords : kb16bitonly

Last Reviewed: July 18, 1997