I tried to sort an array of string using qsort. here is the content of my array:
{"a","orange","apple","mobile","car"}
this is how I use qsort:
int myCompare (const void * a, const void * b ) {
const char *pa = (const char*)a;
const char *pb = (const char*)b;
return strcmp(pa,pb);
}
int stringLen = sizeof(input)/sizeof(char *);
qsort(input, stringLen, sizeof (char*), myCompare);
However, when I print the array, nothing is changed. is there something wrong w/ this?
I've changed your myCompare function to what Mitch Wheat had posted earlier, and that works properly. Here's the example:
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
int myCompare (const void * a, const void * b ) {
const char *pa = *(const char**)a;
const char *pb = *(const char**)b;
return strcmp(pa,pb);
}
int main() {
int i;
const char *input[] = {"a","orange","apple","mobile","car"};
int stringLen = sizeof(input) / sizeof(char *);
qsort(input, stringLen, sizeof(char *), myCompare);
for (i=0; i<stringLen; ++i)
printf("%d: %s\n", i, input[i]);
}
This will return:
0: a
1: apple
2: car
3: mobile
4: orange
qsort(input, stringLen, sizeof (char*), myCompare) calls myCompare to compare strings which are sorted.
myCompare gets pointers to compared values. In our case we get pointers to strings (const char**). So we should compare *(const char**)a and *(const char**)b, which are strings pointed by a and b.
Start debugging with:
int myCompare (const void * a, const void * b ) {
const char *pa = (const char*)a;
const char *pb = (const char*)b;
printf("Comparing %s vs. %s for result %d\n", pa, pb, strcmp(pa,pb));
return strcmp(pa,pb);
}
I think shortly after that, you'll figure out the problem. :)
