Assert

• /usr/include/assert.h declares the function

  void assert(int assertion);
  

  which is very useful in software maintance and debugging.

• Basically, the line

  assert( n >= 0 );
  

  has no affect if n is non-negative, but if n is negative (if the assertion fails) then assert prints out the line number, the source code file name, and the expression ("n >= 0") that failed before terminating the program.

• assert shouldn't be used for communicating errors to the user (who really doesn't care about line numbers and such), but is great for internal consistency checks. If you have a routine that requires X and expects all calling routines to check for X before calling it, put in an assert(X); as the first line of the function. It is good pre-condition documentation, and it will at least tell you your program has failed (rather than your program just mysteriously crashing.)

• If some any reason you are worried about the assert statements in your program taking too long at run-time, you can remove them all by using the -DNDEBUG ("no debug") switch at compile time.