std::async with class member function

Question

I'm kind of new to std::async and I have problems understanding how it works. I saw example of how to pass member funcion to std::async somewhere on the web but it seems not to compile. Whats the problem here? How can it be done without lambda?

class Test {
  std::future<void> f;
  void test() {}
  void runTest() {
    // ERROR no instance overloaded matches argument list
    f = std::async(std::launch::async, &Test::test, this); 

    // OK...
    f = std::async(std::launch::async, [this] {test();}); 
  }
  void testRes() {
    f.get();
  }
};

No, it is not. Tried to keep minimal reproducible example as close as it is in original source :) — michelson
– michelson, Commented Feb 18, 2018 at 23:27
What compiler and version? There's nothing wrong with the code you've shown. Please include headers, main() etc so it's a minimal reproducible example. — Praetorian
– Praetorian, Commented Feb 18, 2018 at 23:34
The information provided here is not sufficient to help you, at best we can only make educated guesses. please post a MCVE — WhiZTiM
– WhiZTiM, Commented Feb 18, 2018 at 23:34

Matthias247 · Accepted Answer · 2018-02-18 23:57:53Z

2

You should be able to use std::bind to create a callable function object:

f = std::async(std::launch::async, std::bind(&Test::test, this));

In your example &Test::test is not a function that takes one parameter of type Test, as it would be expected by std::async. Instead it is member function, which must be called differently.

answered Feb 18, 2018 at 23:57

Matthias247

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