My_strcmp:字符串比较
 

int My_strcmp(const char* arr1, const char* arr2){
    assert(arr1&&arr2);
    while (*arr1 + *arr2 != 0)
    {
        if (*arr1 > *arr2)
            return 1;
        else if (*arr1 < *arr2)
            return -1;
        else
        {
            arr1++; arr2++;
        }
    }
}

My_strcat:字符串追加
 

char* My_strcat(char * arr1, const char* arr2){
    assert(arr1 != NULL);
    assert(arr2 != NULL);
    char* ret = arr1;
    while (*arr1 != '\0')
        arr1++;
    while (*arr1 = *arr2)
    {
        arr1++;
        arr2++;
    }
    return ret;
}

My_strcpy;字符串复制

char* My_strcpy(char* arr1, char* arr2)
{
    char* ret = arr1;
    do
    {
        *arr1 = *arr2;
        arr1++;
        arr2++;
    } while (*(arr2 - 1) != '\0');
    return ret;
}

 

My_strlen:求字符串长短
 

int My_strlen(const char* p){
    char* tmp = p;
    while (*p)
        p++;
    return p - tmp;
}