#define array[]

This is a discussion on #define array[] within the C Programming forums, part of the General Programming Boards category; Hello. I have a problem. I want to define a constant array. Code: #include <stdio.h> #include <stdlib.h> #define array[] {'a', ...

  1. #1
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    #define array[]

    Hello. I have a problem. I want to define a constant array.

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    #define array[] {'a', 'b', 'c'}
    
    
    int main()
    {
      system("clear");
    
      printf("\n\n%c\n\n", array[0]);
    
      return 0;
    }
    when I try to compile with gcc I get that error

    p.c:4:13: warning: missing whitespace after the macro name
    p.c: In function 'main':
    p.c:11: error: syntax error before '[' token


    Any one who knows how to define a constant array? Pleace help? Thank you.

  2. #2
    Epy
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    does const not work?

  3. #3
    The larch
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    This expands to

    Code:
    printf("\n\n%c\n\n", [] {'a', 'b', 'c'}[0]);
    What did you expect?
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  4. #4
    ATH0 quzah's Avatar
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    Quote Originally Posted by anon View Post
    This expands to
    No, it would only expand to that if there was a space after the word array. As-is, it just fails to compile.


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

  5. #5
    The larch
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    Interestingly with GCC it only deserves a warning, with Comeau Online it is an error in C99 mode and a warning in C90 mode.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  6. #6
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    Quote Originally Posted by cs05pp2 View Post
    Any one who knows how to define a constant array? Pleace help? Thank you.
    Code:
    const char array[] = "abc";
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

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  7. #7
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    If I use that code is working and compile:

    Code:
    int main()
    {
    int array[] = {1,2,3,4,5};
    
    printf("%d", array[0]);
    
    return 0;
    }
    but if I try to define it as constant I get an error from the gcc compiler.

    Code:
    #define array[] {1,2,3,4,5};
    int main()
    {
    
    
    printf("%d", array[0]);
    
    return 0;
    How can I define a constant array ? Thank you

  8. #8
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    An array requires a physical location in memory. It cannot be implemented as a simple macro. cpjust's code is the correct way to do this.
    It is too clear and so it is hard to see.
    A dunce once searched for fire with a lighted lantern.
    Had he known what fire was,
    He could have cooked his rice much sooner.

  9. #9
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    If I define

    Code:
    #define array "abcdef"
    
    int main()
    {
    printf("%c", array[0]);
    
    return 0;
    }
    It will work, and the string is an array of characters. So I still believe that I can define a constant array. But I don't know how.

  10. #10
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by cs05pp2
    It will work, and the string is an array of characters. So I still believe that I can define a constant array. But I don't know how.
    Right, but then "abcdef"[0] is valid syntax. Suppose that you did not define a macro. How would you do what you are trying to do? If you cannot do it, then you cannot do it by defining a macro, since preprocessing would result in textual substitution.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  11. #11
    Chi! whiteflags's Avatar
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    #define array "abcdef"

    it only works because "abcdef" is a string literal. There are no other "literal" arrays in C, they should have a proper identifier. If you think that #define makes an identifier out of some phrase, then please review what your text says about the prepocessor: you are wrong.

  12. #12
    cas
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    It can be done in C99 (look up compound literals); but I can't see much of a reason to do so when you can just use const, which is portable to non-C99 compilers.

    The real question is, why are you hell-bent on avoiding the creation of an array and tagging it with const?

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