Templates: I need to learn these better? Why am i getting errors
I am working on someone elses code that is no longer around and it is old CodeWarrior Code. XCode complains about this:
template <class listClass,class itemClass>
void FxStreamingObjectList<listClass,itemClass>::StreamOut(FxStream *stream)
{
if (listClass::size())
{
stream->PutSeparator();
stream->PutString(mFieldName.c_str());
stream->PutSeparator();
stream->PutBeginList();
stream->Indent(+1);
listClass::iterator iter;
for (iter=listClass::begin(); iter != listClass::end(); iter++)
{
stream->PutSeparator();
stream->PutString( (*iter)->GetClassID() );
}
(*iter)->StreamOut(stream);
}
stream->Indent(-1);
stream->PutSeparator();
stream->PutEndList();
stream->PutSeparator();
}
}
I get errors on listClass::iterator iter;
and for (iter=listClass::begin(); iter != listClass::end(); iter++)
that are:
error: expected `;' before 'iter'
error: 'iter' was not declared in this scope
Other places in the same .h, same types of template declarations I get errors开发者_C百科 like:
error: dependent-name 'listClass::iterator' is parsed as a non-type, but instantiation yields a type
at:
for (listClass::iterator iter=listClass::begin(); iter != listClass::end(); iter++)
How do I go about solving these errors? I dont know templates all that well so I am confused and not sure where to begin. A good template resource is also appreciated.
The compiler doesn't know until a bit later in the parsing process that the specific listClass
for any particular instantiation of FxStreamingObjectList<listClass, itemClass>
has a member type called iterator
. The name iterator
is therefore a "dependent name".
You must hint to the compiler that you expect/require iterator
here to be a type, with the typename
keyword:
typename listClass::iterator iter;
and:
for (typename listClass::iterator it = listClass::begin(), end = listClass::end(); it != end; ++it)
(BTW, are begin()
and end()
really static member functions?)
Just another C++ quirk. :)
Officially C++ does not know whether dependent symbols are types or otherwise. To you the programmer listClass::iterator
is obviously a type. The compiler needs some help.
The definition of iter
should be:
typename listClass::iterator iter
The other answers already answered Why the Error
As for the second part of your the Question: A good template resource is also appreciated
The most definitive book on C++ Templates is:
C++ Templates: The Complete Guide by David Vandevoorde & Nicolai Josuttis
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