如何按字母顺序对指针数组进行排序，然后使用qsort？

Question

I am trying to write a function in which I sort the pointers inside of wptrs , an array of pointers to strings in another array. I am challenging myself not to use string.h for this exercise, as I want to understand how a sorting algorithm could work in C. I am using qsort() , however, but I am trying to write a comparison function for it called mycharptrcompare() .

I have looked at how strcmp() works, and I have tried to mimic that with mycharptrcompare() . However, I notice the difference that strcmp() expects a char*, while the mycharptrcompare() function expects a char**. I've written a method called dumpwptrs to show me the contents and how they are organized within wptrs . Thus far, I have the following code:

UPDATE:

I have also tried:

int mycharptrcompare(const void *a, const void *b)
{
  //Need to convert a void * to a more specific type to dereference
  const char *aPtr = a;
  const char *bPtr = b;
  const char **pa = &aPtr;
  const char **pb = &bPtr;

  while (*pa && *pa == *pb) {
    pa++;
    pb++;
  }
  return *pa - *pb;
}

and my output I got was:

(null)

jumps

world

is

dog

blue

Which is still incorrect, because my list should be sorted in alphabetical order, and the first input (the word "hello"), has not been read in.

Answer 1

FYI here is an example use of qsort() .

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

int cmp(const void *a, const void *b)
{
    const char **pa = a;
    const char **pb = b;
    return strcmp(*pa, *pb);
}

int main(void)
{
    char *wptrs[] = { "hello", "jumps", "world", "is", "dog", "blue" };
    size_t len = sizeof wptrs / sizeof wptrs[0];
    qsort(wptrs, len, sizeof wptrs[0], cmp);

    for(size_t i = 0; i < len; i++) {
        printf("%s\n", wptrs[i]);
    }
    return 0;
}

Program output:

blue
dog
hello
is
jumps
world