// ptrsort.c -- 从键盘输入一系列字符串
// 将其按升序或降序排列
// 然后，把排序后的字符串显示在屏幕上
#include <stdio.h>
#include <stdlib.h>
#include <string.h>#define MAXLINES 25int get_lines(char *lines[]);
void sort(char *p[], int n, int sort_type);
void print_strings(char *p[], int n);
int alpha(char *p1, char *p2);
int reverse(char *p1, char *p2);char *lines[MAXLINES]; int main(void){int number_of_lines, sort_type;//从键盘读入多行字符串number_of_lines = get_lines(lines); if(number_of_lines < 0){puts("Memory allocation error");exit(-1);}puts("Enter 0 for reverse order sort, 1 for alphabetical: ");scanf("%d", &sort_type);sort(lines, number_of_lines, sort_type);printf("\n");print_strings(lines, number_of_lines);return 0;
}int get_lines(char *lines[]){int n = 0;char buffer[80];  // 临时储存每一行字符串puts("Enter one lines at time; enter a blank when done.");while(n < MAXLINES && gets(buffer) != 0 && buffer[0] != '\0'){if((lines[n] = (char *)malloc(strlen(buffer) + 1)) == NULL)return -1;strcpy(lines[n++], buffer);}return n;
} // get_lines结束 void sort(char *p[], int n, int sort_type){int a, b;char *x;//函数指针int (*compare)(char *s1, char *s2);// 根据sort_type参数的值，让指针指向相应的比较函数 compare = (sort_type) ? reverse : alpha;
//    if(0 == sort_type){
//        compare = reverse;
//    }
//    if(1 == sort_type){
//        compare = alpha;
//    }for(a = 1; a < n; a++){for(b = 0; b < n-1; b++){if(compare(p[b], p[b+1]) > 0){x = p[b];p[b] = p[b+1];p[b+1] = x;}}}
}  // sort结束 void print_strings(char *p[], int n){int count;for(count = 0; count < n; count++){printf("%s\n", p[count]);}
}int alpha(char *p1, char *p2){ // 按字母顺序比较return (strcmp(p2, p1));
}int reverse(char *p1, char *p2){ //按反向字母比较return (strcmp(p1, p2));
}