Page 60 - C-Language

be disabled by defining the macro NDEBUG.

Another way to terminate a program when an error occurs are with the standard library functions
exit, quick_exit or abort. exit and quick_exit take an argument that can be passed back to your
environment. abort() (and thus assert) can be a really severe termination of your program, and
certain cleanups that would otherwise be performed at the end of the execution, may not be
performed.

The primary advantage of assert() is that it automatically prints debugging information. Calling
abort() has the advantage that it cannot be disabled like an assert, but it may not cause any
debugging information to be displayed. In some situations, using both constructs together may be
beneficial:

if (color == COLOR_RED || color == COLOR_GREEN) {
...
} else if (color == COLOR_BLUE) {
...
} else {
assert(0), abort();
}

When asserts are enabled, the assert() call will print debug information and terminate the
program. Execution never reaches the abort() call. When asserts are disabled, the assert() call
does nothing and abort() is called. This ensures that the program always terminates for this error
condition; enabling and disabling asserts only effects whether or not debug output is printed.

You should never leave such an assert in production code, because the debug information is not
helpful for end users and because abort is generally a much too severe termination that inhibit
cleanup handlers that are installed for exit or quick_exit to run.

Assert Error Messages

A trick exists that can display an error message along with an assertion. Normally, you would write
code like this

void f(void *p)
{
assert(p != NULL);
/* more code */
}

If the assertion failed, an error message would resemble

Assertion failed: p != NULL, file main.c, line 5

However, you can use logical AND (&&) to give an error message as well

void f(void *p)
{
assert(p != NULL && "function f: p cannot be NULL");
/* more code */

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