C++ templates,errors where used std iterators

Question

When I try to compile template class, I got the following errors:

C.cpp: In member function 'void PeriodContainerAdvanced<T>::add()':
C.cpp:133: error: type/value mismatch at argument 1 in template parameter list for 'template<class _T1, class _T2> struct std::pair'
C.cpp:133: error:   expected a type, got 'std::map<int,T,std::less<int>,std::allocator<std::pair<const int, T> > >::iterator'
C.cpp:133: error: invalid type in declaration before ';' token

Class at C.h file: (Simplified)

template <class T>
class PeriodContainerAdvanced 
{
[skip]
    void add (); 
[skip]
}

C.cpp (Simplified):

template <class T>
void PeriodContainerAdvanced<T>::add()
{
[skip]
    std::pair<std::map< time_t, T >::iterator, bool> ret; // line 133 !
[skip]
}

And the similar error at other function when trying to define

std::map< time_t, T >::iterator it, it_start, it_end; // line 153

after this line compiler say:

C.cpp:153: error: expected `;' before 'it'
C.cpp:166: error: 'it_start' was not declared in this scope

How to fix it? thanks

Luchian Grigore · Accepted Answer · 2012-04-25 14:57:41Z

9

That's a dependent name, you'll need to declare it as:

std::pair<typename std::map< time_t, T >::iterator, bool> ret;

Also, to avoid later linker errors, you should move template implementations to a file visible to all translation units that use that template - like the header where you define your template class.

answered Apr 25, 2012 at 14:57

Luchian Grigore

260k68 gold badges465 silver badges634 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

juanchopanza · Accepted Answer · 2012-04-25 15:50:09Z

6

First, need to put the add() implementation in the header file, or in a file included by the header. The compiler needs to see the code in order to instantiate the template for a given T.

Second, the source of the error you quote, you need to add a typename to tell the compiler you are talking about a type. std::map< time_t, T >::iterator could be interpreted as a value.

template <class T>
class PeriodContainerAdvanced {
  void add () {
    std::pair<typename std::map< time_t, T >::iterator, bool> ret;
    ....         ^
  }
};

edited Apr 25, 2012 at 15:50

answered Apr 25, 2012 at 14:59

juanchopanza

228k35 gold badges421 silver badges493 bronze badges

3 Comments

abrahab Over a year ago

its compile without "first" step, only with second. thanks. add defined at the header file like void add (); (see first message) and implemented at C.cpp

juanchopanza Over a year ago

@abrahab OK, that is totally weird, unless your build system is doing something magic. Or maybe you haven't tried using it yet in an executable.

abrahab Over a year ago

already used. seems gcc know that its implementation of the class function, because its defiled as: template <class T> void PeriodContainerAdvanced<T>::add() {..} at C.cpp . Interesting. Its like all others functions at separated .cpp file...

Collectives™ on Stack Overflow

C++ templates,errors where used std iterators

2 Answers 2

Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related