assert()                Diagnostic Message Generator

 #include   <assert.h>
 #include   <stdio.h>

 void       assert(expression);          condition to be evaluated.
 int        expression;

    assert() tests 'expression'. If 'expression' fails, assert() prints a
    diagnostic message and aborts the calling process.   No action is
    taken if 'expression' is true (nonzero), so 'expression' should be
    chosen so it is true if the program is operating correctly.

    The diagnostic message has the form:

       Assertion failed: 'expression', file 'filename', line 'linenumber'

    where 'filename' is the source file name and 'linenumber' is the line
    where assert() appears.  assert() is used to identify program logic
    errors.

       Returns:     No return value

         Notes:     assert() is a macro.

                    If NDEBUG is defined (with any value), the C
                    preprocessor removes all assert() calls from the
                    program.  NDEBUG can be defined via the -D command-
                    line option, or with a #define directive.

   -------------------------------- Example ---------------------------------

    The following statement tests whether pshift is NULL and prints an
    appropriate message.

           #include <assert.h>
           #include <stdio.h>

           struct BASE {
                  char *name;
                  int number;
           } *pshift;

           main()
           {
               assert(pshift != NULL);
                 /* process item */
           }