INFO: Predefined Identifiers in Microsoft C and C++

The information in this article applies to:
This article was previously published under Q65472


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.


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.

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.)

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
   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
   NO_EXT_KEYS         Disables Microsoft-specific language extensions
                       and extended keywords; defined only with /Za

   _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.

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).