23-字符串示例_字符串排序
11.6 字符串示例:字符串排序
我们来处理一个按字母表顺序排序字符串的实际问题。准备名单表、创建索引和许多其他情况下都会用到字符串排序。该程序主要是用 strcmp()
函数来确定两个字符串的顺序。一般的做法是读取字符串函数、排序字符串并打印出来。之前,我们设计了一个读取字符串的方案,该程序就用到这个方案。打印字符串没问题。程序使用标准的排序算法,稍后解释。我们使用了一个小技巧,看看读者是否能明白。程序清单11.29演示了这个程序。
程序清单11.29 sort_str.c
程序
/* sort_str.c -- 读入字符串,并排序字符串 */
#include <stdio.h>
#include <string.h>
#define SIZE 81 /* 限制字符串长度,包括 \0 */
#define LIM 20 /* 可读入的最多行数 */
#define HALT "" /* 空字符串停止输入 */
void stsrt(char *strings [], int num); /* 字符串排序函数 */
char * s_gets(char * st, int n);
int main(void)
{
char input[LIM][SIZE]; /* 存储输入的数组 */
char *ptstr[LIM]; /* 内含指针变量的数组 */
int ct = 0; /* 输入计数 */
int k; /* 输出计数 */
printf("Input up to %d lines, and I will sort them.\n", LIM);
printf("To stop, press the Enter key at a line's start.\n");
while (ct < LIM && s_gets(input[ct], SIZE) != NULL
&& input[ct][0] != '\0')
{
ptstr[ct] = input[ct]; /* 设置指针指向字符串 */
ct++;
}
stsrt(ptstr, ct); /* 字符串排序函数 */
puts("\nHere's the sorted list:\n");
for (k = 0; k < ct; k++)
puts(ptstr[k]); /* 排序后的指针 */
return 0;
}
/* 字符串-指针-排序函数 */
void stsrt(char *strings [], int num)
{
char *temp;
int top, seek;
for (top = 0; top < num - 1; top++)
for (seek = top + 1; seek < num; seek++)
if (strcmp(strings[top], strings[seek]) > 0)
{
temp = strings[top];
strings[top] = strings[seek];
strings[seek] = temp;
}
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
}
我们用一首童谣来测试该程序:
Input up to 20 lines, and I will sort them.
To stop, press the Enter key at a line's start.
O that I was where I would be,
Then would I be where I am not;
But where I am I must be,
And where I would be I can not.
Here's the sorted list:
And where I would be I can not.
But where I am I must be,
O that I was where I would be,
Then would I be where I am not;
看来经过排序后,这首童谣的内容未受影响。