compiler differences

This is a discussion on compiler differences within the C Programming forums, part of the General Programming Boards category; I wrote a program for some research purpose ...anyway the thing is that iam a mac user so i wrote ...

  1. #1
    Registered User white's Avatar
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    Nov 2004
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    39

    compiler differences

    I wrote a program for some research purpose ...anyway

    the thing is that iam a mac user so i wrote the program using a C99 compiler that comes with mac...trying to avoid several C99 only features so as to compile in older compilers and mainly on older compilers running on windows machines.

    the code did compile and it did produce an executable (using Microsoft Visual Studio 2003) but it gave wrong results after a little bit debugging i found out that what was failing was the qsort command.

    here is the code... typical but i would appriciate if anyone can guess(or knows) why it fails...
    Code:
    typedef double T;
    Code:
    int cmp(const void* a, const void* b)
    {
        T ai = *((T*)a), bi = *((T*)b);
        if(ai<bi)
            return -1;
        else if(ai>bi)
            return 1;
        else 
            return 0;
    }

    Code:
    int g;
        for (g = 0; g < i; g++)
        {
            x[g] = real[g].Px;
            y[g] = real[g].Py;
        }
        
        qsort(x, i ,sizeof(real[i].Px), &cmp);
        qsort(y, i ,sizeof(real[i].Py), &cmp);
    the code of course works excellent when compiled with xcode's compiler...the problem is with the window's compiler

  2. #2
    Just Lurking Dave_Sinkula's Avatar
    Join Date
    Oct 2002
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    5,006
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    typedef double T;
    
    int compare(const void *a, const void *b)
    {
       const T *x = a, *y = b;
       if ( *x > *y )
       {
          return 1;
       }
       if ( *x < *y )
       {
          return -1;
       }
       return 0;
    }
    
    int main(void)
    {
       T t[] = {3,2,7,4,6,9,1,3,6,0};
       size_t i;
    
       for ( i = 0; i < sizeof t / sizeof *t; ++i )
       {
          printf("%g,", t[i]);
       }
       putchar('\n');
    
       qsort(t, i, sizeof *t, compare);
    
       for ( i = 0; i < sizeof t / sizeof *t; ++i )
       {
          printf("%g,", t[i]);
       }
       putchar('\n');
    
       return 0;
    }
    
    /* my output
    3,2,7,4,6,9,1,3,6,0,
    0,1,2,3,3,4,6,6,7,9,
    */
    This to me is just easier to read. Watch what you are feeding to qsort.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

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