macro to determine if variable is signed/unsigned

This is a discussion on macro to determine if variable is signed/unsigned within the C Programming forums, part of the General Programming Boards category; #define IS_UNSIGNED( var ) \ ( (var) >= 0 && ~(var) >= 0 ) what are the forseen problems in ...

  1. #1
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    macro to determine if variable is signed/unsigned

    #define IS_UNSIGNED( var ) \
    ( (var) >= 0 && ~(var) >= 0 )

    what are the forseen problems in using this? I see a problem when looking at zero after the integer is one's complemented.

    Can this be modified to accept a variable that is a type, as below?

    #define IS_UNSIGNED( TYPE ) \

  2. #2
    and the hat of wrongness Salem's Avatar
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    Why the fascination with macros - both your threads have been about macros.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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    Senior Member joshdick's Avatar
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    Yeah, a function would be a whole lot better.

    Why don't you just test it? Try it out on 0, 1, -1, and the maxima for integers.

    I don't quite see the need for this function, however. C is a strongly typed language, so the type of a variable shouldn't be ambiguous.
    FAQ

    "The computer programmer is a creator of universes for which he alone is responsible. Universes of virtually unlimited complexity can be created in the form of computer programs." -- Joseph Weizenbaum.

    "If you cannot grok the overall structure of a program while taking a shower, you are not ready to code it." -- Richard Pattis.

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    Smile

    Hey Sal, I don't have a fixation on macros, I am just trying familiarize myself with debugging and ..... I was told this will be helpful on some of new projects- in lieu of some systems work.
    Last edited by Cdigitproc1; 04-29-2005 at 11:47 AM.

  5. #5
    and the hat of wrongness Salem's Avatar
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    Macros cannot be debugged is one thing you should be learning then
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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    Wink

    Thx Sal.

  7. #7
    Gawking at stupidity
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    I don't know about other compilers, but I know gcc provides a means to see your source code after the preprocessor stage but before the compilation stage. You just use the -E switch:
    Code:
    itsme@dreams:~/C$ cat preproc.c
    #define MIN(x,y) (((x) > (y)) ? (y) : (x))
    
    int main(void)
    {
      int a = 5;
      int b = 7;
      int c;
    
      c = MIN(a, b);
    
      return 0;
    }
    Code:
    itsme@dreams:~/C$ gcc -Wall -E preproc.c
    # 1 "preproc.c"
    
    
    int main(void)
    {
      int a = 5;
      int b = 7;
      int c;
    
      c = ((( a ) > (  b )) ? (  b ) : ( a )) ;
    
      return 0;
    }
    itsme@dreams:~/C$
    Maybe you'll find that helpful.
    If you understand what you're doing, you're not learning anything.

  8. #8
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    cpp -E in most unixen does the same thing as gcc -E or cc -E - it runs the precompiler and redirects output to stdout.

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