Cpp Dev Programming Forum

DarkVader · Today

I have a problem with "qsort" function included in the <stdlib.h>

Code:

# include <stdio.h>
# include <stdlib.h>

int numcomp(int*, int*);

struct a {
    int s [max];
    int x ;
};
  

int main(){
........
........
/*Where  (void**)(p->s) is a int array,
max is dimension of array, 
sizeof(int) indicate size of array element,
(int(*)(void*,void*))numcomp) is a pointer to function "numcomp" that return a "int" and it have how parameters (int*,int*).*/

qsort((void**)(p->s),max,sizeof(int),(int(*)(void*,void*))numcomp);

return 0;

}

Now the compiler get me this error :

" Description Resource Path Location Type
passing argument 4 of â€˜qsortâ€™ from incompatible pointer type sort.c /struct line 63 C/C++ Problem "

Why? Help me, please.

p.s. I used for compiler this program Eclipse (Cygwin) on Windows 7.

dave79 · Today

The prototype for the standard C library function qsort() is

Code:

 void qsort(void *base, size_t nmemb, size_t size,
                  int(*compar)(const void *, const void *));

To avoid the compiler complaint, make the cast on the fourth argument match the prototype exactly. Note that const void * is not the same as void *. This is important to the compiler, and should be important to you.

If you declare the function properly, you don't need a cast when you call it. In a code review, when I see a program with casts where they shouldn't be needed, it's a red flag for me. I mean, it's not necessarily "wrong" to put a cast even if you don't need it, but casting can hide problems that otherwise might have been detected by the compiler. See Footnote.

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Cpp Dev Programming Forum

#1 Today

How to use qsort?

Code:

#2 Today

Re: How to use qsort?

Code:

#3 Today

Re: How to use qsort?

#4 Today

Re: How to use qsort?

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