帧头 帧尾问题

#include <stdio.h>

#include <string.h>

char   *head_count(char *str, char *head)//找出帧头前面的字符串

{

char *temp;

int size_head = strlen(head);

int count1 = 0;

int head_flag = 0;

if(str == NULL || head == NULL)

{

return NULL;

}

if(strlen(str) < strlen(head))

{

return NULL;

}

while(*str != '\0' && !head_flag)//判断找出dead

{

while(*str == *head)

{

str++;

head++;

count1++;

if(count1 == size_head)

{

    head_flag = 1;

temp = str - size_head;//temp表示帧头出现位置前的字符

break;

}

}

str++;

}

if(head_flag)

{

return temp;

}

else

{

printf("error!");

}

}

char  *tail_count(char *str, char *tail)//找出到帧尾为止的所有的字符串

{

if(str == NULL || tail == NULL)

{

return NULL;

}

if(strlen(str) < strlen(tail))

{

return NULL;

}

    int size_tail = strlen(tail);

int count2 = 0;

int tail_flag = 0;

int head_flag = 1;

if(head_flag)

{

while(*str != '\0' && !tail_flag)//判断寻找出帧尾

{

while(*str == *tail)

{

    str++;

tail++;

count2++;

if(size_tail == count2)

{

    tail_flag = 1;

break;

}

}

str++;

}

}

if(tail_flag)

{

return str - 1;//返回的是到帧尾结束的字符串

}

else

{

printf("error!");

}

}

int main()

{

int i;

char *str = "asdheadhauboisoktail";

char *head = "head";

char *tail = "tail";

char *str_head = head_count(str, head);

char *str_tail = tail_count(str,tail);

printf("输入的字符串为:");

printf("%s\n",str);

printf("合法的帧为:");

int n = str_tail - str_head;

for(i = 0;i < n;i++)//输出合法的帧

{

printf("%c",*str_head);

str_head++;

}

printf("\n");

    return 0;

}