19.函数名: strrev

功  能: 串倒转
用  法: char *strrev(char *str);
程序例:

#include <string.h>
#include <stdio.h>
int main(void)
{
   char *forward = "string";
   printf("Before strrev(): %s
", forward);
   strrev(forward);
   printf("After strrev():  %s
", forward);
   return 0;
}

20.函数名: strset

功  能: 将一个串中的所有字符都设为指定字符
用  法: char *strset(char *str, char c);
程序例:

#include <stdio.h>
#include <string.h>
int main(void)
{
   char string[10] = "123456789";
   char symbol = 'c';
   printf("Before strset(): %s
", string);
   strset(string, symbol);
   printf("After strset():  %s
", string);
   return 0;
}

21.函数名: strspn

功  能: 在串中查找指定字符集的子集的第一次出现
用  法: int strspn(char *str1, char *str2);
程序例:

#include <stdio.h>
#include <string.h>
#include <alloc.h>
int main(void)
{
   char *string1 = "1234567890";
   char *string2 = "123DC8";
   int length;
   length = strspn(string1, string2);
   printf("Character where strings differ is at position %d
", length);
   return 0;
}