Compile errors using std::bind in gcc 4.7

Question

I am having a lot of trouble using std::bind in various places of my code. Sometimes it works, sometimes it doesn\'t, so I assume I am doing something fundament

Answer 1

The placeholder position objects (e.g. when you use _2) is not the position of the argument in the function you call, but a placeholder for the argument in the created callable object. Instead always start with _1 and increase.

So:

auto bar_auto=std::bind(foo,1,_1);

etc.

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This means you can switch the arguments in the object created by std::bind by simply doing like

auto bar_auto=std::bind(foo,_2,_1);

When you "call" the bar_auto object, the first argument will be the second argument to foo, and the second argument in the call will be the first argument to foo.

Answer 2

The _2 placeholder means to use second argument of the returned functor. Therefore the type of

std::bind(foo,1,_2)

is not std::function<int(int)> but

std::function<int(unspecified_type, int)>

To get std::function<int(int)>, use

std::bind(foo, 1, _1)
//                ^^