Passing lambdas to std::thread and calling class methods

Question

I\'m having a bit of trouble using std::thread together with lambdas. I have a method TheMethod where I should use std::thread to parallelize some function calls to methods

Answer 1

This is because the objects cursor and a are passed by value to the constructor of thread. The functor takes a reference to the local copies of the newly created thread and not on the objects you expected them to be .

Hence, as answered by "alexk7", you should use std::ref or if you want to capture them pass by reference

Answer 2

You can use std::ref to pass the parameters by reference:

std::thread t1(functor, std::ref(cursor), std::ref(a))

You could also capture the parameters by reference in the lambda itself:

size_t a;
Cursor cursor = someCursor();
std::thread t1([&] {a = classMethod(cursor);});
t1.join();