B.6 Diagnostics:

The assert macro is used to add diagnostics to programs:   void assert(int expression) If expression is zero when   assert(expression) is executed, the assert macro will print on stderr a message, such as   Assertion failed: expression, file filename, line nnn It then calls abort to terminate execution. The source filename and line number come from the preprocessor macros __FILE__ and __LINE__. If NDEBUG is defined at the time <assert.h> is included, the assert macro is ignored