memstr 从内存找字符串

#include

char* memstr(char* full_data, int full_data_len, char* substr)
{
    if (full_data == NULL || full_data_len <= 0 || substr == NULL) {
        return NULL;
    }
 
    if (*substr == '\0') {
        return NULL;
    }
 
    int sublen = strlen(substr);
 
    int i;
    char* cur = full_data;
    int last_possible = full_data_len - sublen + 1;
    for (i = 0; i < last_possible; i++) {
        if (*cur == *substr) {
            //assert(full_data_len - i >= sublen);
            if (memcmp(cur, substr, sublen) == 0) {
                //found
                return cur;
            }
        }
        cur++;
    }
 
    return NULL;
}

int main()
{
  char a[26] ={'q','w','e','r','t','y','u','i','o','p','a','s','d','f','\0','h','j','k','\0','z','x','c','v','b','n','m'};
  char *ret = memstr(a,26,"zxcv");
  
  int b = ret - a;

  printf("z  %d\n",b);
}

得到结果

z 19