Posted on 4 Aug 2009 at 6:00 AM

View this post at the Programmers Heaven C++ forum.


Dear fellow programmers,



I fail to get a typedef in a template class to compile, when using G++ 3.4.4 (compiled with 'g++ UnitMyClass.cpp'). But when I use C++ Builder 6's compiler (BCC32) it compiles successfully.

Below are the simplified code and error messages. Note that I already try to tackle the problem with four different syntaxes.

Google didn't give me the answer, I hope you will.



Thanks in advance, Bilderbikkel


//UnitMyClass.cpp

#include "UnitMyClass.h"







//UnitMyClass.h

#include <map>

 

template <class T> struct MyClass

{

  typedef T value_type;

  void MyMethod_1() const

  {

    typedef std::map<T,double>::const_iterator Iter;

  }

  void MyMethod_2() const

  {

    typedef std::map<value_type,double>::const_iterator Iter;

  }

  void MyMethod_3(const T& t) const

  {

    typedef std::map<T,double>::const_iterator Iter;

  }

  void MyMethod_4(const T& t) const

  {

    typedef std::map<value_type,double>::const_iterator Iter;

  }

};

The errors (for each version of MyMethod) are:


$ g++ UnitStorage.cpp

In file included from UnitStorage.cpp:5:

UnitStorage.h: In member function 'void MyClass<T>::MyMethod_1() const':

UnitStorage.h:15: error: expected init-declarator before "Iter"

UnitStorage.h:15: error: expected ',' or ';' before "Iter"

Answer by Lundin


Surprisingly I actually knew that one!



It's because of GCC being strict with the standard and Borland ain't. You gotta write

 

typedef typename std::map<T,double>::const_iterator Iter;

 

However, I don't enough of the C++ standard to explain the details of that.

Thanks Lundin!

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(C++) My Questions: Expected init-declarator compiler-error with G++

Answer by Lundin