c++: async throw C2752 and C2064

Question

I had hard time understanding how to use async function.

I don't want to use boost library but just want to run a function asynchronously, so I ask your help:

• How to use async to make this code working ?
• Is there any other way of doing this ?

Here's a piece of my code:

void KWxAPI::update(bool const no_interact)
{
async(launch::async, &KWxAPI::syncUpdate, no_interact);
}

bool KWxAPI::syncUpdate(bool const nointeract)
{
    //blablabla
}

And here are the errors the build gimme: See on pastebin

I really hope you'll help me cause I come from Java and C++ is much harder :C

EDIT: I'm using MSVC.

Answer 1

Your code doesn't compile because you're trying to invoke a pointer to a member function, without passing the object to invoke it on.

KWxAPI::syncUpdate needs a KWxAPI object to use as it's this pointer, but you aren't passing one. Any time you try to invoke a pointer-to-member function, such as this, you need to pass the this pointer it should use as the first parameter.

std::async(std::launch::async, &KWxAPI::syncUpdate, this, no_interact);

Aside from this, you should be aware that KWxAPI::syncUpdate will execute in another thread, but your std::async statement will block until that thread finishes executing the function.

This is because std::async returns an std::future object, which is destructed at the end of your std::async statement, because you aren't storing it anywhere. In it's destructor, it blocks until execution has completed.