c++11 static functional member variable

Question

Well, I'm stumped. I've always had a bit of a hard time with static member variables and functions, so if the answer to this is really obvious, I apologize. I can't figure out what's wrong, though.

In WSGrid.h:

#include <functional>

class WSGrid
{
public:
    //constructors...

    static const std::function< char( void ) > _randomChar;

    //private data...
};

In WSGrid.cpp:

#include <random>

std::default_random_engine generator;
std::uniform_int_distribution< char > distribution;

const WSGrid::_randomChar = std::bind( distribution, generator );

In my main.cpp:

#include "WSGrid.h"
#include <iostream>

int main( int argc, char* argv[] )
{
    std::cout << WSGrid::_randomChar() << std::endl;
    return 0;
}

And when I try to compile (g++ -std=c++11 -Wall -pedantic main.cpp), I get "undefined reference to WSGrid::_randomChar".

So... it looks, to me, like I'm doing everything right. I'm following the syntax found here, at least as far as I'm aware. But apparently there's something wrong.

Answer 1

You need to define _randomChar correctly.

update :

const WSGrid::_randomChar = std::bind( distribution, generator );

to:

const std::function<char(void)> WSGrid::_randomChar = std::bind(distribution, generator);

Also you need to link WSGrid.cpp

g++ -std=c++11 -Wall -pedantic -c WSGrid.cpp -o WSGrid.o
g++ -std=c++11 -Wall -pedantic main.cpp WSGrid.o