What is wrong with my usage of C++ standard library's find?
c++, std, templates, typename
Solution
std::vector<T>::iterator iter = /* .... */;
`iterator` is a dependent name (effectively, it depends on the type parameter `T`). Dependent names are assumed not to name types unless you use `typename`:
typename std::vector<T>::iterator iter = /* .... */;
For more, consider reading the Stack Overflow C++ FAQ entry "Where and why do I have to put “template” and “typename” on dependent names?"
You will also need to use `const_iterator`, since `list` is const-qualified. You should probably drop the exception specification as well; it's best to "never write an exception specification."
Problem
I'm trying to use the C++ standard library's `find` algorithm like this: ``` 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); } ``` When I try to compile, I get these errors: ``` 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 ``` I feel like the "dependent-name ‘std::vector::iterator’ is parsed as a non-type, but instantiation yields a type" bit holds the key to understanding what I'm doing wrong, but my pea-brain cannot extract the meaning. Update: I needed to add a `typename`, as per the accepted answer, and also use a `const_iterator`, so the problematic line of code became: ``` typename std::vector<T>::const_iterator iter = std::find(list.begin(), list.end(), node); ```