Subject: Re: Null values do not compile... 2007-10-03 - By Maarten Schrijvers
Back
OK. I Google'd and saw many people had similar problems with ambiguity in
VS2005. However, I didn't find how they resolved their problems (if at all).
So I decided to create a work-around which I would like to share:
Passing a "(NULL)" string to my database where a trigger sets that value to
a proper SQL null.
Quite simple actually, just a pain in the butt to maintain it in two places,
but hey can't have it all ;)
2007/10/2, Maarten Schrijvers <maarten.schrijvers@(protected)>:
>
> I have some fields which can be (SQL) NULL. If they are filled they are
> varchar, but they're not necessary, so they could be NULL.
> Compiling gives me an error though:
>
> c:\mysql++\include\null.h(206) : error C2593: 'operator =' is ambiguous
>
> 1> E:\Program Files\Microsoft Visual Studio 8\VC\include\xstring(923):
> could be 'std::basic_string<_Elem,_Traits,_Ax>
> &std::basic_string<_Elem,_Traits,_Ax>::operator =(_Elem)'
>
> 1> with
>
> 1> [
>
> 1> _Elem=char,
>
> 1> _Traits=std::char_traits<char>,
>
> 1> _Ax=std::allocator<char>
>
> 1> ]
>
> 1> E:\Program Files\Microsoft Visual Studio 8\VC\include\xstring(918): or
> 'std::basic_string<_Elem,_Traits,_Ax>
> &std::basic_string<_Elem,_Traits,_Ax>::operator =(const _Elem *)'
>
> 1> with
>
> 1> [
>
> 1> _Elem=char,
>
> 1> _Traits=std::char_traits<char>,
>
> 1> _Ax=std::allocator<char>
>
> 1> ]
>
> 1> E:\Program Files\Microsoft Visual Studio 8\VC\include\xstring(913): or
> 'std::basic_string<_Elem,_Traits,_Ax>
> &std::basic_string<_Elem,_Traits,_Ax>::operator =(const
> std::basic_string<_Elem,_Traits,_Ax> &)'
>
> 1> with
>
> 1> [
>
> 1> _Elem=char,
>
> 1> _Traits=std::char_traits<char>,
>
> 1> _Ax=std::allocator<char>
>
> 1> ]
>
> 1> while trying to match the argument list '(mysqlpp::sql_varchar,
> mysqlpp::null_type)'
>
> 1> c:\mysql++\include\null.h(204) : while compiling class template member
> function 'mysqlpp::Null<Type>::operator Type(void)'
>
> 1> with
>
> 1> [
>
> 1> Type=mysqlpp::sql_varchar
>
> 1> ]
>
> 1> e:\visual studio
> 2005\projects\t_1\urenregistratie\Relatieonderhoud.h(25) : see reference to
> class template instantiation 'mysqlpp::Null<Type>' being compiled
>
> 1> with
>
> 1> [
>
> 1> Type=mysqlpp::sql_varchar
>
> 1> ]
>
> I have declared the following:
>
> typedef
> mysqlpp::Null<mysqlpp::sql_varchar> Nullstr;
>
> static
> Nullstr vVoornamen = mysqlpp::null; //gave the variable a value trying to
> avoid the error
>
> What am I doing wrong?
>
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