Using ## to concatenate tokens

This is a discussion on Using ## to concatenate tokens within the C Programming forums, part of the General Programming Boards category; Hi everyone. I'm trying to get my code to automatically print out string literals called MESSAGE1, MESSAGE2, etc. However, the ...

  1. #1
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    Using ## to concatenate tokens

    Hi everyone. I'm trying to get my code to automatically print out string literals called MESSAGE1, MESSAGE2, etc. However, the compiler tells me that it cannot find MESSAGEi. This isn't what I want, obviously. How do I do it properly?

    Richard

    Code:
    #define MESSAGE(i) MESSAGE##i
    #define MESSAGELINES 2
    #define MESSAGE1 "First string"
    #define MESSAGE2 "Second string"
    
    	int i ;
    	for ( i = 0 ; i < MESSAGELINES ; i++ )
    		printf ( "%s" , MESSAGE(i) );
    	return 0;
    ]

  2. #2
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    Token concatenation occurs at preprocessing time. However, you're trying to make up the name by accessing the value of the variable `i', which is unavailable to the preprocessor as it can be only known at runtime.
    Stick close to your desks and never program a thing,
    And you all may sit in the standards commitee!

  3. #3
    ATH0 quzah's Avatar
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    It wouldn't work anyway, because you start i at 0, so you'd be trying to make MESSAGE0 and MESSAGE1, not MESSAGE1 and MESSAGE2.


    Quzah.
    Hope is the first step on the road to disappointment.

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