[PATCH 1/5] Add the field checking for missing value after opration

[Zhang Xiliang]

Hello Steve,

>  	if (v == NULL || f == v)
>  		return -1;

I have some questions for "f == v".

I think it only checks the address of "f" and "v". It seems unuseful.
If we need to check whether the value is equal to the field, I think we should use strcmp().
What your opinion about it?
If you agree with me, I will make another patch for it.