What include am I missing?

Question

I'm trying to compile the following program:

#include<functional>
#include<iostream>

int main(int argc, char* argv[], char* env[]) {
  std::function<int(int, int)> f = [i, &j] { return i + j; };
  std::cout << f(5, 5);
}

Why do I get the following error:

a.cc:17:3: error: \u2018function\u2019 is not a member of \u2018std\u2019

Even if I replace it with "auto" the compiler complains that "f" doesn't name a type. I tried with GCC 4.4.3 and 4.6.2.

Answer 1

std::function<int(int, int)> f = [i, &j] { return i + j; };

That is wrong syntax.

What you actually want to write is this:

std::function<int(int, int)> f =[](int i, int j) { return i + j; };

Or if you want to use auto , then:

auto f =[](int i, int j) { return i + j; };

Use -std=c++0x option with gcc-4.6.2 to compile this code.

Answer 2

Polymorphic wrappers for function objects are new in C++11. To use these features in a pre-4.7 GCC installation that supports C++0x (the draft version of C++11), you need to compile with the -std=c++0x switch (see here ).

For GCC v4.7, that is switched to -std=c++11 (see here ).