Implement strstr

我正在尝试从头开始编写strstr函数。我在调试器中逐行检查了我的代码，它运行得很好。但是，它没有正确保存搜索的子字符串的开头。因此，它没有适当地归还它。我没有太多编程经验，所以我的代码有点混乱和复杂。然而，它在大多数情况下确实有效。下面是我的代码（为我的教授和大家评论，看看我做了什么）。（此外，我的教授已经表示接受后藤函数）

char *strgstr(const char *str1, const char *str2)
{
    //I went through this function line by line with the debugger
    //The only problem with it is when I go to save the location of the
    //substring in str1.  
    //I posted a question on stackoverflow and I was able to get it to compile
    //but it still doesn't save and return properly.  The rest of the function works.
    int len_str1=strlen(str1);
    int len_str2=strlen(str2);
    char *save_str=NULL;
    int i=0;
    for(; i<len_str1; i++)
    {
there:
        if(str1[i]==str2[0])            //checks if this is the beginning of str2
        {
            save_str=(char*)str1[i];    //This is where the problem is. 
            int j=0;                    //start at beginning of str2
            for(;i<len_str1;i++)        //index str1
            {
                if(j<len_str2)          //checks if we've finished searching str2
                {
                    if(str1[i]!=str2[j])
                    {
                        goto there;
                    }
                    j++;
                }
                else
                {
                    return save_str;    //does not return properly.  I can't figure out how to save a particular point in the index to a pointer. 
                }
            }
        }
    }
}