assigning std::function to a member function

Question

class A {
public:
  std::function<void(int)> f_;
  void print_num(int i) {
    cout << i;
  }
  void setFuntion(std::function<void(int)> f) {
    f_=f;
  }
  void run() {
    setFunction(print_num);
  }
};

this doesn't work. i get note: no known conversion for argument 1 from ‘<unresolved overloaded function type>’ to ‘std::function<void(int)>’ and other errors.

If I put the definition of print_num outside of the class. everything works. i tried adding &A::, A:: and this. nothing helped.

score 3 · Accepted Answer · edited May 23 '17 at 11:56

3

print_num is a non-static member function, which means that it has an implicit first argument of type A*. You can, for instance, pass that by using a lambda:

void run() { 
    auto myself = this;
    setFunction( [myself] (int i) { myself->print_num (i); } ); 
}

or use bind, see here

c++ Trouble casting overloaded function: <unresolved overloaded function type>

edited May 23 '17 at 11:56

Community

1
1

answered Oct 11 '12 at 06:49

JohnB

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5

ehh, and i thought std::function should have made things easier :-( – kirill_igum Oct 11 '12 at 06:55
`setFunction( [this] (int i) { this->print_num (i); } );` also worked – kirill_igum Oct 11 '12 at 07:05
Using `[this]` makes a copy of the object, so you probably want `[&this]`, or just `[&]`. – wjl Oct 11 '12 at 23:55
3

Does it? `this` is a pointer, so using `[this]` should make a copy of the pointer. – JohnB Oct 12 '12 at 06:12

assigning std::function to a member function

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