Is it possible to compare #ifdef values for conditional use

c++ conditional c-preprocessor preprocessor-directive
Jasmine picture Jasmine · Aug 12, 2014 · Viewed 23.1k times · Source

I'm trying to come up with a generic, easy to use way to only run certain code, depending upon the api I am using at the time.

In a header:

#define __API_USED cocos2d-x

#define COCOS2DX  cocos2d-x
#define OPENGL opengl

#ifdef __API_USED == COCOS2DX
    #define USING_COCOS2DX
    #undef USING_OPENGL
#endif

in source:

#ifdef USING_COCOS2DX
    ......
#endif

However I don't think this would work.

Is there a way to accomplish what I am looking to do?

Answer

Ross Ridge picture Ross Ridge · Aug 12, 2014

You can but you need to do it like this:

#define __API_USED COCOS2DX

#define COCOS2DX  1
#define OPENGL 2

#if __API_USED == COCOS2DX
    #define USING_COCOS2DX
    #undef USING_OPENGL
#endif

As Keith Thompson explained undefined tokens (macros) like cocos2d and x evaluate to 0 so you need to define values for the macros you're using.

Related questions

Type condition in template

Is it possible to build only some part of the code given the type of the template in C++ ? It would be something lake that : #include <iostream> using namespace std; template<typename T> void printType(T …

Read More
C++ Multiple statements for conditional operator

I'm trying to use a conditional statement that does one thing in one condition but does two things if the other condition applies. Consider the following: ( h >= 0 && h < 24 ? hour = h : hour = 0, cout << "Invalid Hour …

Read More
How to use something like a continue statement in nested for loops?

I have a class of objects and need to compare one property of each object to the same property of all other objects. If they match, the code needs to do something. This results in two 'for loops' looping through …

Read More