GCC 的宏預定義列表

http://gcc.gnu.org/onlinedocs/cpp/Predefined-Macros.html 

Several object-like macros are predefined; you use them without supplying their definitions. They fall into three classes: standard, common, and system-specific.

In C++, there is a fourth category, the named operators. They act like predefined macros, but you cannot undefine them.

• Standard Predefined Macros
• Common Predefined Macros
• System-specific Predefined Macros
• C++ Named Operators

 有用的實例：打印當前的文件名和行號

__FILE__

This macro expands to the name of the current input file, in the form of a C string constant. This is the path by which the preprocessor opened the file, not the short name specified in ‘#include’ or as the input file name argument. For example, "/usr/local/include/myheader.h" is a possible expansion of this macro. 

__LINE__

This macro expands to the current input line number, in the form of a decimal integer constant. While we call it a predefined macro, it's a pretty strange macro, since its “definition” changes with each new line of source code.

__FILE__ and __LINE__ are useful in generating an error message to report an inconsistency detected by the program; the message can state the source line at which the inconsistency was detected. For example,

     fprintf (stderr, "Internal error: "
                      "negative string length "
                      "%d at %s, line %d.",
              length, __FILE__, __LINE__);