Inserting <string, function pointer> into map

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.

I'm using g++. Hmm.. Made the template function a bit more specific. — ggg
– ggg, Commented Jun 26, 2010 at 6:16
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. — Ben Voigt
– Ben Voigt, Commented Jun 26, 2010 at 6:24
@Ben, write that as a short answer and you will get credit for it and @ggg will be able to accept an answer. — David Rodríguez - dribeas
– David Rodríguez - dribeas, Commented Jun 26, 2010 at 9:35
@David: I had a slight advantage from answering (fixing the typedef) on his previous question, in which the out-of-line definition of DoThing was provided, and it was clearly a class member (but without the declaration there was still no indication of whether or not it was static). — Ben Voigt
– Ben Voigt, Commented Jun 26, 2010 at 14:35

Ben Voigt · Accepted Answer · 2010-06-26 14:33:49Z

5

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, e.g. &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.

answered Jun 26, 2010 at 14:33

Ben Voigt

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Comments

Shinjikun · Accepted Answer · 2010-06-26 05:44:45Z

1

You forgot a ',' before the second &.

answered Jun 26, 2010 at 5:44

Shinjikun

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andreas buykx · Accepted Answer · 2010-06-26 06:07:08Z

1

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.

answered Jun 26, 2010 at 6:07

andreas buykx

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1 Comment

ggg Over a year ago

That could certainly have been one of the problems, but didn't solve it.

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