Is #if defined MACRO equivalent to #ifdef MACRO?

Question

I have code that I want to have two modes, debug and verbose. I define them in my header file as,

#define verbose TRUE #define debug TRUE 

In my code so far, I have just been using

#if(debug)   //code #endif 

but is it more proper to use?

#ifdef debug   // code #endif 

I read something about preprocessor macros but it didn't make sense at the time. So, I have a question: Is #if defined MACRO equivalent to #ifdef MACRO? and which one is better for enabling/disabling a particular section of code?

Answer 1

#ifdef MACRO #if defined (MACRO) 

will do the exact same thing. However, the defined (MACRO) is just an expression that evaluates to 0 or 1 inside the #if, and it can be combined with other expressions. For example

#if defined (MACRO) && ! defined (MACRO2)     // Do this #else     // Do that #endif 

Try doing that with #ifdef - you can't unless your code gets really clumsy.

Answer 2

#if defined(MACRO) is the same as #ifdef MACRO, but is longer. On the other hand it allows to add extra conditions with || or &&.

#if MACRO is similar to #ifdef MACRO but not 100%. If MACRO is 0 then #if MACRO will be negative - it requires MACRO to be defined and not be 0. #ifdef checks only whether it is defined even without value (#define MACRO).

Now is modern to use #if and enable/disable definitions with value 1 or 0:

#define FLAG_X 1 // or 0