输入一个字符串,同时输入帧头和帧尾(可以是多个字符),将该字符串中合法的帧识别出来

提示:帧头和帧尾分别是head和tail  字符串”asdheadhauboisoktail”中headhauboisoktail是合法帧

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

int main()
{
    char str[30] = {0};
    char a[30] = {0};
    char b[30] = {0};
    printf("请输入一个字符串，侦头和侦尾：\n");
    scanf("%s%s%s",str,a,b);

    char *ptr = str;
    char *a1 = a;
    char *b1 = b;
    char *a2 = NULL;

    int len_a, len_b, i;
    len_a = strlen(a);
    len_b = strlen(b);

    while(*ptr != '\0')
    {   
        if(strncmp(ptr, a1, len_a) == 0)
        {
            a2 = ptr;
            while(*a2 != '\0')
            {
                if(strncmp(a2, b1, len_b) == 0)
                {
                    int sum = a2 - ptr + len_b;
                    for(i = 0; i < sum; i++)
                    {
                        printf("%c",*ptr);
                        ptr++;
                    }
                }
                else
                {
                    puts("error\n");
                    return 0;
                }
                a2++;
            }
         }
         else
         {
            puts("error\n");
            break;
         }
        ptr++;
    }   
    printf("\n");
    return 0;
}