__LINE__
  __FILE__
  __DATE__
  __TIME__
  _cplusplus
  __STDC__

The following variables can vary by compiler, but generally work:

• The __LINE__ and __FILE__ variables represent the current line and current file being processed.
• The __DATE__ variable contains the current date, in the form month/day/year. This is the date that the file was compiled, not necessarily the current date.
• The __TIME__ variable represents the current time, in the form hour:minute:second. This is the time that the file was compiled, not necessarily the current time.
• The _cplusplus variable is only defined when compiling a C++ program.
• The __STDC__ variable is defined when compiling a C program, and may also be defined when compiling C++.