CODEWITHSUNDEEP
cstrcmpqsort
wakajawaka
wakajawaka

Reputation: 1

passing argument 4 of qsort from incompatible pointer type

please help with this warning:

passing argument 4 of qsort from incompatible pointer type;

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define BSIZE 200
int (*cmp)(void *, void *);
int main(int argc, char *argv[]){

  FILE *in;
  char buf[BSIZE];
  int i, nofl;
  char *p[20];



  if(argc<2){
    printf("too few parameters...\n");
    return 1;
}
  in=fopen(argv[1], "r+b");
  if(in == NULL){
    printf("can't open file: %s\n", argv[1]);
    return 0;
}

  while(fgets(buf,BSIZE+1,in)){
    p[i]=malloc(strlen(buf)+1);
    strcpy(p[i],buf);

    i++;
}

  nofl=i;

  qsort(p,nofl,sizeof(int), &cmp);

  for(i=0;i<nofl;i++)
    printf("%s\n",p[i]);

  return 0;
}

int (*cmp)(void *a, void *b){
  int n1 = atoi(*a);
  int n2 = atoi(*b);
  if (n1<n2)
    return -1;
  else if (n1 == n2)
    return 0;
  else
    return 1;
}

i think this c program must convert string to int and sort by asc. the problem is that with qsort strngs massive takes no effect, it stays the same as unsorted.

Upvotes: 0

Views: 2041

Answers (1)

R Sahu
R Sahu

Reputation: 206737

int (*cmp)(void *a, void *b){ ... }

is not legal code to define a function.

Instead of

int (*cmp)(void *, void *);

use

int cmp(const void*, const void*);

Update, in response to comment by OP

int cmp(const void *a, const void *b){

  // Here, a is really a pointer to a `char*`.

  const char* pa = *(const char**)a;
  const char* pb = *(const char**)b;

  int n1 = atoi(pa);
  int n2 = atoi(pb);

  // Simplify the return value.
  return ((n1 > n2) - (n1 < n2));

  /***
  if (n1<n2)
    return -1;
  else if (n1 == n2)
    return 0;
  else
    return 1;
  ***/

}

Upvotes: 2

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