Description of the predefined identifiers in Microsoft C and C++

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SUMMARY

The information below is from the Microsoft C Compiler versions 6.0, 6.0a, and 6.0ax; C/C++ version 7.0; Visual C++ 1.0 and 1.5 for Windows; and Visual C++ 1.0 for Windows NT online Help.

The following information can be accessed in C 6.0 and C/C++ 7.0 from the help on CL.EXE by seeking help on the text "cl" using either the F1 key from the Programmer's WorkBench (PWB) or by typing "qh cl" from the MS-DOS or OS/2 command lines. From the "CL Contents" help screen, select Preprocessor Options, then Predefined Identifiers.

This information can be accessed in Visual C++ for Windows and Visual C++, 32-bit Edition, by searching on _MSC_VER in the Microsoft C/C++ Language Help.

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MORE INFORMATION

The compiler automatically defines identifiers useful in writing portable programs. You can use these identifiers to compile code sections conditionally. These identifiers are always defined unless otherwise stated.

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Microsoft specific

Note These macros are supported by both the 16-bit and 32-bit compilers.

   Macro               Specifies
   ------------------------------------------------------------------

   _CHAR_UNSIGNED      Default char type is unsigned. Macro defined
                       when /J is specified.
   M_I86,  _M_I86      Always defined. Identifies target machine as a
                       member of the 8086 family.
   _MSC_VER            Microsoft C version; currently defined as 800.

The following symbol was added in C/C++ 7.0:

   Macro               Specifies
   --------------------------------------------------------------------

   __cplusplus         Macro defined when compiling a C++ program. (This
                       macro is not defined for the C compiler.)

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16-bit specific

   Macro               Specifies
   -------------------------------------------------------------------

   MSDOS, _MSDOS       Always defined. Identifies target operating system
                       as MS-DOS.
   M_I86mM, _M_I86mM   Always defined. Member of the I86 processor family.
                       Memory model type:
                       m = T   Tiny
                       S   Small (default)
                       C   Compact model
                       M   Medium model
                       L   Large model
                       H   Huge model
                       Macros defined by /AT, /AS, /AC, /AM, /AL, and /AH
                       respectively.
   M_I8086, _M_I8086   8088 or 8086 processor; default or defined when /G0
                       is specified.
   M_I286, _M_I286     80286 processor. Macro defined when /G1 or /G2 is
                       specified.
   NO_EXT_KEYS         Disables Microsoft-specific language extensions
                       and extended keywords; defined only with /Za
                       option.

   _QC                 Supported for compatibility with Microsoft C version
                       6.0. The _FAST macro (or /f) is the default and is
                       the recommended alternative.

The following symbols were added in C/C++ 7.0:

   Macro               Specifies
   -------------------------------------------------------------------

   _DLL                Code for run-time library as a dynamic-link library.
                       Defined when /MD is specified.
   _FAST               Fast-Compile. Macro defined when /f is specified
                       Supersedes _QC, which is still supported but not
                       recommended. Using /Od causes CL to compile your
                       program with /f. The /f option compiles source files
                       without any default optimizations.
   __STDC__            Full conformance with the ANSI C standard. Defined
                       the integer constant 1 only if the /Za command-line
                       option is given; otherwise is undefined.
   _PCODE              Defined for sections of code that are compiled as
                       p-code. Macro defined when /Oq is enabled.
   _WINDLL             Windows protected-mode dynamic-link library is
                       selected with /GD.
   _WINDOWS            Windows protected-mode is selected with /GA, /Gw,
                       /GW, /Mq, or /GD.

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32-bit specific

The following symbols were added in Visual C++, 32-bit Edition, version 1.0:

   Macro               Specifies
   -----               ---------

   _DLL                Defined when Multithreaded using DLL (/MD or /MDd)
                       is specified.

   _M_IX86             Defined as 300 for the 80386 processor (/G3 option),
                       as 400 for the 80486 (/G4) processor, as 500
                       for the Pentium processor (/G5), and as 600 for 
                       Pentium Pro and Pentium II processors (/G6).

   _MT                 Defined when Multithreaded (/MD, /MDd, /MT, or /MTd)


   _WIN32              Defined for WIN32 applications. Always defined.
                       Microsoft specific.

The following symbols were added in Visual C++, 32-bit Edition, version 4.0:

   Macro               Specifies
   -----               ---------

   _CPPRTTI            Defined for code compiled with Enable Run-Time Type
                       Information (/GR).

   _CPPUNWIND          Defined for code compiled with Enable Exception
                       Handling (/GX).

The _MSC_VER macro will have one of the following values depending upon the particular Microsoft compiler:

   Compiler                           _MSC_VER value
   --------                           --------------
   C Compiler version 6.0                  600
   C/C++ compiler version 7.0              700
   Visual C++, Windows, version 1.0        800
   Visual C++, 32-bit, version 1.0         800
   Visual C++, Windows, version 2.0        900
   Visual C++, 32-bit, version 2.x         900
   Visual C++, 32-bit, version 4.0         1000
   Visual C++, 32-bit, version 5.0         1100
   Visual C++, 32-bit, version 6.0         1200

Note If a predefined identifier has two forms, with and without an underscore, the command-line driver defines both if you specify the /Ze option (compile for Microsoft extensions). It defines only the leading underscore form if you specify the /Za option (compile for ANSI compatibility).

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APPLIES TO

Microsoft Visual C++ 1.0 Professional Edition
Microsoft Visual C++ 1.5 Professional Edition
Microsoft Visual C++ 2.0 Professional Edition
Microsoft Visual C++ 4.0 Standard Edition
Microsoft Visual C++ 6.0 Service Pack 5
Microsoft Visual C++ 5.0 Standard Edition

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kbcompiler kbinfo KB65472

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Retired KB Content Disclaimer

This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.

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