Debugging Messages in C

Many of you learned to program in systems that had no debugger. Hence, you debug by printing out messages. This is not a bad idea, but it is certainly less good than using a debugger. If you insist on printing error messages, at least do it in a way that lets you turn them off. Here's one possibility.

Step 1. The Header File

Create a file, debug.h, that you include in programs that you might debug. The file should look something like the following.

#ifndef _DEBUG_H_
#define _DEBUG_H_

#include <stdio.h>

/* Macros to help in debugging.  Compile your program with -DDEBUG
 * if you want debugging messages printed.  Don't use the -DDEBUG
 * if you don't want the messages printed.  Print your debugging 
 * messages with S_NOTE(string) and I_NOTE(string,int).  For example,
 *
 *   S_NOTE("Entered factorial");
 *   I_NOTE("N", N);
 *
 * Author: Sam Rebelsky
 * Verson: 1.0 of February 2000
 */
 
#ifdef DEBUG

#define S_NOTE(str) fprintf(stderr, "DEBUG: %s\n", str)
#define I_NOTE(i) fprintf(stderr, "DEBUG: %s is %d\n", i)

#else

#define S_NOTE(str)
#define I_NOTE(i)

#endif /* DEBUG */

#endif /* _DEBUG_H_ */

Step 2. Add Messages to Your Code

Whenever you want a simple string message printed, use

S_NOTE(message);

Whenever you want to print an integer variable, use

I_NOTE(variable_name,variable)

Step 3. Compile Appropriately

When you want debugging messages on, compile your program with -DDEBUG. When you don't want debugging messages on, compile your program without it. If you use make, it helps to define a CFLAGS variable.

CFLAGS=-DDEBUG
CC=gcc