C++ How to Program, 10/e

E.9 Assertions

The assert macro—defined in the <cassert> header file—tests the value of an expression. If the value of the expression is 0 (false), then assert prints an error message and calls function abort (of the general utilities library—<cstdlib>) to terminate program execution. This is a useful debugging tool for testing whether a variable has a correct value. For example, suppose variable x should never be larger than 10 in a program. An assertion may be used to test the value of x and print an error message if the value of x is incorrect. The statement would be

assert( x <= 10 );

If x is greater than 10 when the preceding statement is encountered in a program, an error message containing the line number and file name is printed, and ...