为什么在这个模板中使用typedef是必要的？ [英] Why is the use of typedef in this template necessary?

问题描述

当我在Visual Studio 2005中编译此代码时：

When I compile this code in Visual Studio 2005:

  template <class T>
  class CFooVector : public std::vector<CFoo<T>>
  {
  public:
    void SetToFirst( typename std::vector<CFoo<T>>::iterator & iter );
  };

  template <class T>
  void CFooVector<T>::SetToFirst( typename std::vector<CFoo<T>>::iterator & iter )
  {
    iter = begin();
  }

我得到这些错误：

c:\home\code\scantest\stltest1\stltest1.cpp(33) : error C2244:     'CFooVector<T>::SetToFirst' : unable to match function definition to an existing declaration
    c:\home\code\scantest\stltest1\stltest1.cpp(26) : see declaration of 'CFooVector<T>::SetToFirst'
    definition
    'void CFooVector<T>::SetToFirst(std::vector<CFoo<T>>::iterator &)'
    existing declarations
    'void CFooVector<T>::SetToFirst(std::_Vector_iterator<_Ty,_Alloc::rebind<_Ty>::other> &)'

$ b b

如果我添加一个typedef到CFooVector模板，我可以得到代码编译和工作：

If I add a typedef to the CFooVector template, I can get the code to compile and work:

  template <class T>
  class CFooVector : public std::vector<CFoo<T>>
  {
  public:
    typedef typename std::vector<CFoo<T>>::iterator FooVIter;
    void SetToFirst( FooVIter & iter );
  };

  template <class T>
  void CFooVector<T>::SetToFirst( FooVIter & iter )
  {
    iter = begin();
  }

我的问题是，为什么typedef在使用裸< $ c>'typename std :: vector> :: iterator'声明无效？

My question is, why does the typedef work when using the bare 'typename std::vector>::iterator' declaration did not work?

推荐答案

这也编译好，并揭示了VC ++混淆 - 分配器类型的来源。显然在类VS之外选择不同的默认值。

This compiles as well and reveals the source of VC++ confusion -- allocator type. Apparently outside of the class VS selects different default. Or maybe it can't recognize them to be the same.

在VS2008上（按原样）和VS2003（在>之间有空格）进行编译

Compiles on VS2008 (as is) and VS2003 (with space between >>)

template <class T>
class CFoo
{
public:
    T m_t;
};

template <class T>
class CFooVector : public std::vector<CFoo<T>>
{
public:
    void SetToFirst(typename std::vector<CFoo<T>, typename CFooVector::_Alloc>::iterator & iter);

};

template <class T>
void CFooVector<T>::SetToFirst( typename std::vector<CFoo<T>, typename CFooVector::_Alloc>::iterator & iter )
{
    iter = begin();
}

GCC 3.4想要this-> begin（）和space，编译代码没有显式的分配器类型...肯定看起来像MS编译器不那么聪明，因为它应该是...

GCC 3.4 wanted this->begin() and space, but otherwise it can compile the code without explicit allocator type... Definitely looks like MS compiler not as smart as it should be...

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