Question

我正在尝试使用C ++标准库的find算法，如下所示：

  template<class T>
  const unsigned int AdjacencyList<T>::_index_for_node(
      const std::vector<T>& list, const T& node
  ) throw(NoSuchNodeException)
  {
    std::vector<T>::iterator iter = std::find(list.begin(), list.end(), node);
  }

当我尝试编译时，我收到了这些错误：

In file included from ../AdjacencyList.cpp:8:
../AdjacencyList.h: In member function ‘const unsigned int Graph::AdjacencyList<T>::_index_for_node(const std::vector<T, std::allocator<_Tp1> >&, const T&)’:
../AdjacencyList.h:99: error: expected ‘;’ before ‘iter’
../AdjacencyList.h:100: error: ‘iter’ was not declared in this scope
In file included from ../AdjacencyListTest.cpp:9:
../AdjacencyList.h: In member function ‘const unsigned int Graph::AdjacencyList<T>::_index_for_node(const std::vector<T, std::allocator<_Tp1> >&, const T&)’:
../AdjacencyList.h:99: error: expected ‘;’ before ‘iter’
../AdjacencyList.h:100: error: ‘iter’ was not declared in this scope
../AdjacencyList.h: In member function ‘const unsigned int Graph::AdjacencyList<T>::_index_for_node(const std::vector<T, std::allocator<_Tp1> >&, const T&) [with T = int]’:
../AdjacencyList.h:91:   instantiated from ‘const std::vector<T, std::allocator<_Tp1> > Graph::AdjacencyList<T>::neighbours(const T&) [with T = int]’
../AdjacencyListTest.cpp:18:   instantiated from here
../AdjacencyList.h:99: error: dependent-name ‘std::vector::iterator’ is parsed as a non-type, but instantiation yields a type
../AdjacencyList.h:99: note: say ‘typename std::vector::iterator’ if a type is meant

我觉得“依赖名称'std :: vector :: iterator'被解析为非类型，但是实例化产生了一种类型”bit是理解我做错了什么的关键，但是我的豌豆-brain无法提取意义。

更新：我需要根据接受的答案添加typename，并使用const_iterator，因此有问题的代码行变为：

    typename std::vector<T>::const_iterator iter = std::find(list.begin(), list.end(), node);

Answer 1

std::vector<T>::iterator iter = /* .... */;

iterator是一个从属名称（实际上，依赖类型参数T）。除非您使用typename：

，否则假定从属名称不是名称类型

typename std::vector<T>::iterator iter = /* .... */;

有关更多信息，请参阅Stack Overflow C ++ FAQ条目"Where and why do I have to put “template” and “typename” on dependent names?"

您还需要使用const_iterator，因为list是const限定的。您也应该删除异常规范; "never write an exception specification."

最好

我使用C ++标准库的查找有什么问题？

1 个答案: