Clean tracing

There are a couple of problems with the tracing code shown in the previous section.

• There is no way to turn off the tracing.
• There are messy if(..) { trace(...); } fragments all over the place.

We address these problems, we add the following macros

	#ifndef TRACE_INT_STACK
	  #if( NTRACE )
	    #define TRACE_INT_STACK	0
	  #else
	    #define TRACE_INT_STACK	1
	  #endif
	#endif

	#if( TRACE_INT_STACK )

	  #define TRC(_p,_a0)	\
	    ((lcl_trace_int_stack != (_p))? ((void)0):\
	    	trace( __FILE__, __LINE__, (_p), (_a0)))

	  #define TRC1(_p,_a0,_a1)	\
	    ((lcl_trace_int_stack != (_p))? ((void)0):\
	    	trace( __FILE__, __LINE__, (_p), (_a0), (_a1)))
	#else
	  #define TRC(_x,_a0)		((void)0)
	  #define TRC1(_x,_a0,_a1)	((void)0)
	#endif

Using these macros the examples are written as:

	int_stack
	make_int_stack(void)
	{
	  /* ... */

	  TRC(stack, "make_int_stack");
	  return stack;
	}

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

	  TRC1( stack, "push_int_stack %d", val);

	  /* ... */
	}

Now lets examine the macros.

• As usual, we want to be able to control tracing using compiler -D flags; therefore we use #ifndef TRACE_INT_STACK
• When building a shippable executable, we may want to turn off all tracing. Consequently, we use -DNTRACE=1 to turn tracing off.
• The TRC() and TRC1() macros are defined to be do-nothings ((void)0) if TRACE_INT_STACK is 0.
• If TRACE_INT_STACK is 1, the TRC() and TRC1() macros compare the stack against lcl_trace_int_stack, and if equal, call trace() with the appropriate parameters.