Question

The VS2008 SP1 documentation talks about std::tr1::mem_fun.

So why, when I try and use std::tr1::mem_fun, why do I get this compile error?:

'mem_fun' : is not a member of 'std::tr1' 

At the same time, I can use std::tr1::function without problems.

Here is the sample code I am trying to compile, which is supposed to call TakesInt on an instance of Test, via a function<void (int)>:

#include 'stdafx.h' #include <iostream> #include <functional> #include <memory>  struct Test { void TakesInt(int i) { std::cout << i; } };  void _tmain()  {     Test* t = new Test();      //error C2039: 'mem_fun' : is not a member of 'std::tr1'     std::tr1::function<void (int)> f =         std::tr1::bind(std::tr1::mem_fun(&Test::TakesInt), t);     f(2); } 

I’m trying to use the tr1 version of mem_fun, because when using std::mem_fun my code doesn’t compile either! I can’t tell from the compiler error whether the problem is with my code or whether it would be fixed by using tr1’s mem_fun. That’s C++ compiler errors for you (or maybe it’s just me!).

---

Update: Right. The answer is to spell it correctly as mem_fn!

However when I fix that, the code still doesn’t compile.

Here’s the compiler error:

error C2562:  'std::tr1::_Callable_obj<_Ty,_Indirect>::_ApplyX' :   'void' function returning a value 

Answer 1

Change it to this:

std::tr1::function<void (int)> f =     std::tr1::bind(std::tr1::mem_fn(&Test::TakesInt), t, std::tr1::placeholders::_1); f(2); 

The binder requires the int argument. So you have to give it a placeholder which stands for the integer argument that the generated function object needs.

Btw: I’m not sure whether you already know this or not. But you don’t need that mem_fn for this. Just change it to

std::tr1::function<void (int)> f =     std::tr1::bind(&Test::TakesInt, t, std::tr1::placeholders::_1); f(2);