cppreference.com > C/C++ Pre-processor Commands > Predefined preprocessor variables Predefined preprocessor variables Syntax:
      __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. The __TIME__ variable represents the current time, in the form hour:minute:second. 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++.