Using VERIFY()

Using verify_int_stack() as described previously has some serious drawbacks.

• When an assert() inside the verify_ fails, it reports the line number of the verify_ routine, not the line number of the function calling the verify_, which is the line number that we are really interested in.
• verify_ can be fairly expensive. One may wish to enable/disable them independent of assert() - in particular, they need an enabling mechanism independent of NDEBUG.
• If verification is disabled, then it makes no sense to even call the verify_ function; its just wasted work.

To correct the first two problems, we will modify define a macro like assert(), but one that uses an external file and line number.

	/* this belongs in some project-wide common header */
	#if( NVERIFY )
	  #define verify(_file, _line, _e)	((void)0)
	#else
	  #define verify(_file, _line, _e) \
		((_e)?	(void)0: \
			( fprintf(stderr, "%s %d: verify failure: %s", \
				_file, _line, #_e), \
			  abort()))
	#endif
		  

Note that one can disable verification by defining NVERIFY to 1; this is different from disabling assert(). In that case defining NDEBUG to anything will cause assert() to be disabled.

We also have to modify the verify_ routine to accept the callers file and line numbers:

	void
	verify_int_stack(
		FILE *		file,
		int		line,
		const int_stack	stack
		)
	{
	  verify( file, line, len_int_stack(stack) >= 0 );
	  verify( file, line, len_int_stack(stack) <= max_int_stack(stack) );
	  verify( file, line, max_int_stack(stack) >= 16 );
	  verify( file, line, ((max_int_stack(stack) - 16)%16) == 0 );
	}

Finally, we have to control the actual calling of the verify_ function. To do this we define the following macros:

	#if( NVERIFY )
	  #define VERIFY_INT_STACK(_stack)	((void)0)
	#else
	  #define VERIFY_INT_STACK(_stack) \
	  	verify_int_stack(__FILE__, __LINE__, _stack)
	#endif

Using this macro, the code for push_int_stack() will look like:

	void
	push_int_stack(
		int_stack	stack,
		int		val
		)
	{
	  /* definitions ... */

	  VERIFY_INT_STACK(stack);

	  /* body ... */

	  VERIFY_INT_STACK(stack);
	}