How to use std::bind to bind a function with object pointer param?

Question

Following is my code:

class A {};
class Test
{
public:
    template <class TClass>
    Test(TClass* _objPointer, void(TClass::*_func)(A*))
    {
        mEventFunction = std::bind(_func, _objPointer);
    }
private:
    std::function<void(A*)> mEventFunction;
};

class Demo
{
public:
    void BindFunc()
    {
        mTest = new Test(this, &Demo::testFunc);
    }
    void testFunc(A*)
    {

    }
private:
    Test* mTest;
};

What I want to achieve is BindFunc() in Demo class. But this code run with lot of error message: error C2672: 'std::invoke': no matching overloaded function found ......

std::bind(_func, _objPointer, std::placeholders::_1).

T.C.
– T.C.

2017-01-12 12:48:44 +00:00
Commented Jan 12, 2017 at 12:48 — T.C.
– T.C., Commented Jan 12, 2017 at 12:48

AndyG · Accepted Answer · 2017-01-12 12:50:10Z

5

You need to include a std::placeholders::_1 to account for the A* argument that you haven't bound yet:

#include <functional>

class A {};
class Test
{
public:
    template <class TClass>
    Test(TClass* _objPointer, void(TClass::*_func)(A*))
    {
        mEventFunction = std::bind(_func, _objPointer, std::placeholders::_1);
    }
private:
    std::function<void(A*)> mEventFunction;
};

class Demo
{
public:
    void BindFunc()
    {
        mTest = new Test(this, &Demo::testFunc);
    }
    void testFunc(A*)
    {

    }
private:
    Test* mTest;
};

Demo

I think it's a little clearer that you need some placeholder for A* if we used a lambda instead (Demo2):

template <class TClass>
Test(TClass* _objPointer, void(TClass::*_func)(A*))
{
    mEventFunction = [_objPointer, _func](A* _a){(_objPointer->*_func)(_a);};
}

Here the lambda accepts an argument for A*, which is what you wanted. I actually recommend the lambda approach over std::bind in nearly all use cases.

answered Jan 12, 2017 at 12:50

AndyG

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2 Comments

NathanOliver Over a year ago

Kudos for preferring the lambda to bind.

Yonghui Over a year ago

Thank you, this is a great answer!

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