Question

在第5章K＆amp; R C编程模块11中

有一个排序代码示例，用于解释函数指针。

我有两个问题。

在main函数中，为何投选(void**)lineptr？
我收到警告：

此行中出现的指针类型不匹配

qsort1((void**)lineptr,0,nlines-1, (int (*)(void *,void*))(numeric ? numcmp : strcmp));

我仍然没有想出来解决这个错误。

您可以阅读以下代码

提前致谢。

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


#define MAXLEN 1000
#define ALLOCSIZE 1000000 /*size of available space*/
#define MAXLINES 5000


char *lineptr[MAXLINES];

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

void qsort1(void *lineptr[],int left,int right , int (*comp)(void *,void *));
int numcmp(char *,char *);

int getline(char *,int);
char *alloc(int);


static char allocbuf[ALLOCSIZE];
static char *allocp = allocbuf;


main(int argc , char *argv[]){
    int nlines;
    int numeric = 0; /*1 if numeric sort*/

    if(argc > 1 && strcmp(argv[1],"-n") == 0)
        numeric  = 1;
    if((nlines = readlines(lineptr,MAXLINES)) >= 0 ){
        qsort1((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;
    }
}
int readlines(char *lineptr[],int maxlines){
    int len,nlines;
    char *p,line[MAXLEN];

    nlines = 0;
    while((len = getline(line,MAXLEN)) > 0 )
        if(nlines >= maxlines || (p=alloc(len)) == NULL)
            return -1;
        else{
                line[len-1] = '\0';
                strcpy(p,line);
                lineptr[nlines++] = p;
        }

}
void writelines(char *lineptr[],int nlines){
        int i;
        for(i=0;i<nlines;i++)
            printf("%s\n",lineptr[i]);
}


void qsort1(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);
    qsort1(v,left,last-1,comp);
    qsort1(v,last+1,right,comp);
}

int numcmp(char *s1,char *s2)
{
    double v1,v2;

    v1 = atof(s1);
    v2 = atof(s2);
    if(v1<v2)
        return -1;
    else if(v1>v2)
        return 1;
    else 
        return 0;
}
void swap(void *v[],int i, int j){

    void *temp;

    temp = v[i];
    v[i] = v[j];
    v[j] = temp;
}
int getline(char *s,int max){
    int c,i;

    for(i=0 ;  (c=getchar()) != EOF && c != '\n';i++)
        *s++ = c;
    if(c == '\n'){
        *(s+i) = c;
          i++;  

    }
    *(s+i) = '\0';
    return i;
}

char *alloc(int n)
{
    if(allocbuf + ALLOCSIZE - allocp >= n){
        allocp += n;
        return allocp - n;
    }else
        return 0;
}

K＆amp; R排序示例

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