Passing code as an argument (C ++)

Question

How do I go about passing a code block to a function in C ++. In C #, I can do something like this:

void Example(Action action)
{
    action();
}

Example(() => {
    //do something
});

All help and advice is appreciated.

Answer 1

Here is a simple example to start with ...

void Example(void (*x)(void))
{
    x();
}

and the challenge will be ...

Example([] { cout << "do something\n"; });

This is very similar to your C # example. And there are better, more universal ways to do this, as the comments show. If you wanted to return a value and take a parameter, you could do something like this ...

int Example2(int (*y)(int i), int p)
{
    return y(p);
}
// ...
auto ret = Example2([](int p) -> int { cout << p << "\n"; return p; }, 2);

It will be similar to the C # version as follows

int Example2(Func<int,int> y, int p)
{
    return y(p);
}
// ...
var ret = Example2((p) => { /*etc*/ return p; }, 2);

Answer 2

C ++ 11 equivalent:

void Example(const std::function<void()>& action)
{
    // always good to make sure that action has a valid target
    if(action != nullptr)
        action();
}

Example([] {
    //do something
});

Answer 3

std::function<Result(Param1, Param2, ...)> , :

• . - C ++ 98.

  void example(void (*action)()) {
      action();
  }
  
  void example_action() {
      std::cout << "action\n";
  }
  
  example(example_action);
  

• , . Lambdas ++ 11 .

  void example(void (*action)()) {
      action();
  }
  
  example([]() {
      std::cout << "action\n";
  });
  

• ( operator()) , ( "" ).

  template<class F>
  void example(F action) {
      action();
  }
  
  int x = 4;
  example([x]() {
      std::cout << "action (" << x << ")\n";
  });
  
  struct example_action {
      void operator()() {
          std::cout << "action\n";
      }
  };
  
  example(example_action());
  

• std::function , .

  void example(std::function<void()> action) {
      action();
  }
  
  int x = 4;
  example([x]() {
      std::cout << "action (" << x << ")\n";
  });
  

• .

  template<void (*action)()>
  void example() {
      action();
  }
  
  example<example_action>();
  

, # 3 example , , , . # 4 , example . # 5 , , inlining.

Answer 4

std::function<void()> Action ++ -:

void Example(std::function<void()> action)
{
    action();
}

Example([]() {
    //do something
});

std::function, @Les , lambdas, .