字符串函数的实现

char* _strstr(char* haystack,char* needle)
{ 
    //逐位
    for(;;++haystack)
    { 
        char* h = haystack; 
        for(char* n = needle;;++n,++h)
        { 
            //匹配段空返回
            if(!*n)
                return haystack; 
            //1.先找到需要比较的开头 2.比较当前字符
            if(*h !=*n)
                break; 
        } 
        if(!*h)return NULL; 
    } 
} 
void *mymemcpy(void *dest, const void *src, size_t count)
{
    if(dest==NULL || src==NULL)
    {
        return NULL;
    }
    char * temp_dest =(char*)dest;
    char * temp_src = (char*)src;
    while(count--)
    {
        *temp_dest++ = *temp_src++;
    }
    return dest;
}

char * mystrcpy(char * strDest,const char * strSrc)
{
    if(strDest==NULL || strSrc==NULL)
    {
        return NULL;
    }
    char * temp_src =(char *)strSrc;
    while( (*strDest++ = *temp_src++)!= '\0');
    return strDest;

}

unsigned int mystrlen(const char *src)
{
    if(src==NULL)
    {
        return NULL;
    }
    size_t count=;
    while(*src++!='\0')
        count++;
    return count;

}