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Question

I'm having trouble with inserting some value_pairs into a map. Here's the basic idea.

// private
typedef Foo* (*Bar)( const std::string &x, int y );
typedef std::map<std::string, Bar> myMap;

template<class T>
Foo* DoThing( const std::string &x, int y ) {
  return new T( x, y );
}

myMap m_map;

// some map insertion code
m_map.insert( myMap::value_type( "blah", &DoThing<SomeType> ));
m_map.insert( myMap::value_type( "blech", &DoThing<OtherType> ));

This would give a compiler error saying no matching function call to std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, Foo* (*)(const std::string&, int)>::pair(const char [5], <unresolved overloaded function type>) Not sure what I'm doing wrong syntactically, or why I'm getting the unresolved overloaded function type . My best guess is that it doesn't know that DoThing returns a Foo* .

Any help appreciated, thanks.

Answer 1

Comment converted to answer:

Just to be sure, DoThing<T> is a global function and not a member of any class, right? If it's inside a class, it needs to be a static member function.

Also, if you take the address of a member function, some compilers insist on qualifying it with the class name, eg &MyClass::DoThing<T> . Again, if it is a static member function, you get an ordinary function pointer. If a non-static member function, you get a pointer-to-member and the this pointer must be supplied at the call site.

Answer 2

您在第二个＆之前忘记了'，'。

Answer 3

My guess is that it doesn't know how to convert the "blah" and "blech" to std::strings. If you construct these explicitly I think it should work.