Predefined Macros
The compiler recognizes six predefined ANSI C macros (see Table 1.1), and the Microsoft C++ implementation provides several more (see Table 1.2). These macros take no arguments and cannot be redefined. Their value (except for __LINE__ and __FILE__) must be constant throughout compilation. Some of the predefined macros listed below are defined with multiple values. Their values can be set by selecting the corresponding menu option in the Visual C++ development environment, or by using a command-line switch. See the tables below for more information.
Table 1.1 ANSI Predefined Macros
| Macro | Description |
| __DATE__ | The compilation date of the current source file. The date is a string literal of the form Mmm dd yyyy. The month name Mmm is the same as for dates generated by the library function asctime declared in TIME.H. |
| __FILE__ | The name of the current source file. __FILE__ expands to a string surrounded by double quotation marks. |
| __LINE__ | The line number in the current source file. The line number is a decimal integer constant. It can be altered with a #line directive. |
| __STDC__ | Indicates full conformance with the ANSI C standard. Defined as the integer constant 1 only if the /Za compiler option is given and you are not compiling C++ code; otherwise is undefined. |
| __TIME__ | The most recent compilation time of the current source file. The time is a string literal of the form hh:mm:ss. |
| __TIMESTAMP__ | The date and time of the last modification of the current source file, expressed as a string literal in the form Ddd Mmm Date hh:mm:ss yyyy, where Ddd is the abbreviated day of the week and Date is an integer from 1 to 31. |
Table 1.2 Microsoft-Specific Predefined Macros
| Macro | Description |
| _CHAR_UNSIGNED | Default char type is unsigned. Defined when /J is specified. |
| __cplusplus | Defined for C++ programs only. |
| _CPPRTTI | Defined for code compiled with /GR (Enable Run-Time Type Information). |
| _CPPUNWIND | Defined for code compiled with /GX (Enable Exception Handling). |
| _DLL | Defined when /MD or /MDd (Multithread DLL) is specified. |
| _M_ALPHA | Defined for DEC ALPHA platforms. It is defined as 1 by the ALPHA compiler, and it is not defined if another compiler is used. |
| _M_IX86 | Defined for x86 processors. See Table 1.3 for more details. |
| _M_MPPC | Defined for Power Macintosh platforms. Default is 601 (/QP601). See Table 1.4 for more details. |
| _M_MRX000 | Defined for MIPS platforms. Default is 4000 (/QMR4000). See Table 1.5 for more details. |
| _M_PPC | Defined for PowerPC platforms. Default is 604 (/QP604). See Table 1.6 for more details. |
| _MFC_VER | Defines the MFC version. Defined as 0x0421 for Microsoft Foundation Class Library 4.21. Always defined. |
| _MSC_EXTENSIONS | This macro is defined when compiling with the /Ze compiler option (the default). Its value, when defined, is 1. |
| _MSC_VER | Defines the compiler version. Defined as 1200 for Microsoft Visual C++ 6.0. Always defined. |
| _MT | Defined when /MD or /MDd (Multithreaded DLL) or /MT or /MTd (Multithreaded) is specified. |
| _WIN32 | Defined for applications for Win32®. Always defined. |
As shown in following tables, the compiler generates a value for the preprocessor identifiers that reflect the processor option specified.
Table 1.3 Values for _M_IX86
| Option in Developer Studio | Command-Line Option | Resulting Value |
| Blend | /GB | _M_IX86 = 500 (Default. Future compilers will emit a different value to reflect the dominant processor.) |
| Pentium | /G5 | _M_IX86 = 500 |
| Pentium Pro | /G6 | _M_IX86 = 600 |
| 80386 | /G3 | _M_IX86 = 300 |
| 80486 | /G4 | _M_IX86 = 400 |
Table 1.4 Values for _M_MPPC
| Option in development environment | Command-Line Option | Resulting Value |
| PowerPC 601 | /QP601 | _M_MPPC = 601 (Default) |
| PowerPC 603 | /QP603 | _M_MPPC = 603 |
| PowerPC 604 | /QP604 | _M_MPPC = 604 |
| PowerPC 620 | /QP620 | _M_MPPC = 620 |
Table 1.5 Values for _M_MRX000
| Option in Developer Studio | Command-Line Option | Resulting Value |
| R4000 | /QMR4000 | _M_MRX000 = 4000 (Default) |
| R4100 | /QMR4100 | _M_MRX000 = 4100 |
| R4200 | /QMR4200 | _M_MRX000 = 4200 |
| R4400 | /QMR4400 | _M_MRX000 = 4400 |
| R4600 | /QMR4600 | _M_MRX000 = 4600 |
| R10000 | /QMR10000 | _M_MRX000 = 10000 |
Table 1.6 Values for _M_PPC
| Option in Developer Studio | Command-Line Option | Resulting Value |
| PowerPC 601 | /QP601 | _M_PPC = 601 |
| PowerPC 603 | /QP603 | _M_PPC = 603 |
| PowerPC 604 | /QP604 | _M_PPC = 604 (Default) |
| PowerPC 620 | /QP620 | _M_PPC = 620 |