pointers to functions: can't compile

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

#define MAXLINES 5000
char *lineptr[MAXLINES];

int readlines(char *lineptr[], int nlines);
void writelines(char *lineptr[], int nlines);

void qsort(void *lineptr[], int left, int right, int (*comp)(void *, void *));

int numcmp(char *, char *);

int main(int argc, char *argv[])
{
    int nlines;
    int numeric = 0;

    if(argc > 1 && strcmp(argv[1], "-n") == 0)
       numeric = 1;
    if((nlines = readlines(lineptr, MAXLINES)) >= 0) {
        qsort((void **) lineptr, 0, nlines - 1, (int (*)(void *, void *))(numeric ? numcmp : strcmp));
        writelines(lineptr, nlines);
        return 0;
    } else {
           printf("input too big to sort\n");
           return 1;
    }


}

void qsort(void *v[], int left, int right, int(*comp)(void *, void *))
{
     int i, last;
     void swap(void *v[], int, int);

     if(left >= right)
        return;

     swap(v, left, (left + right) / 2);
     last = left;
     for(i = left + 1; i <= right; i++) 
        if((*comp)(v[i], v[left]) < 0)
           swap(v, ++last, i);
     swap(v, left, last);
     qsort(v, left, last - 1, comp);
     qsort(v, last + 1, right, comp);
}

This is direct source code from K&R, in chapter pointers and functions, and this is the example they showed about pointers to functions, but I just can't compile the line in which I call QSORT(line 22). I get this:

22 C:\Users\SUZI\Desktop\solutions\Chapter 5\Exercise 5-14\sort.c conditional expression between distinct pointer types `int (*)(char*, char*)' and `int (*)(const char*, const char*)' lacks a cast 

22 C:\Users\SUZI\Desktop\solutions\Chapter 5\Exercise 5-14\sort.c invalid conversion from `int (*)(char*, char*)' to `void*' 

22 C:\Users\SUZI\Desktop\solutions\Chapter 5\Exercise 5-14\sort.c inv开发者_StackOverflowalid conversion from `int (*)(const char*, const char*)' to `void*' 

---

You are compiling with an ANSI C compiler instead of a good-old K&R C compiler.

The error message is quite clear, look at the const mismatches. Change your function to have the same signature as the qsort function requires, and then cast the arguments inside.

---

Try changing line 22 to:

qsort((void **) lineptr, 0, nlines - 1, (numeric ? (int (*)(void *, void *))numcmp : (int (*)(void *, void *))strcmp));