Search code examples
c++multithreadingqtstdthread

Starting a member function with arguments in a separate thread

I have a member function MyClass::doStuff(QString & str)

I am trying to call that function from a thread like this:

std::thread thr(&MyClass::doStuff, this);

However, that results in an error:

/usr/include/c++/4.8.2/functional:1697: error: no type named ‘type’ in ‘class std::result_of<std::_Mem_fn<void (MyClass::*)(QString&)>(MyClass*)>’ typedef typename result_of<_Callable(_Args...)>::type result_type;

So I've attempted to give it the argument:

QString a("test");
std::thread thr(&MyClass::doStuff(a), this);

However, that results in this error: lvalue required as unary ‘&’ operand

How would I go about running that member function with an argument, from a separate thread?

Solution

  • Just add the arguments to the thread's constructor:

    QString a("test");
std::thread thr(&MyClass::doStuff, this, a);

    As your function accepts a reference you should use std::ref() like this:

    MyClass::doStuff(QString& str) { /* ... */ }

// ...

QString a("test");
std::thread thr(&MyClass::doStuff, this, std::ref(a)); // wrap references