CODEWITHSUNDEEP
c++multithreadingc++11parameter-passingstdthread
ragingcorgi
ragingcorgi

Reputation: 3478

Pass multiple arguments into std::thread

I'm asking about the <thread> library in C++11 standard.

Say you have a function like:

void func1(int a, int b, ObjA c, ObjB d){
    //blahblah implementation
}

int main(int argc, char* argv[]){
    std::thread(func1, /*what do do here??*/);
}

How do you pass in all of those arguments into the std::thread? I tried listing the arguments like:

std::thread(func1, a,b,c,d);

But it complains that there's no such constructor. One way to get around this is defining a struct to package the arguments, but is there another way to do this?

Upvotes: 90

Views: 194025

Answers (5)

Jiř&#237;
Jiř&#237;

Reputation: 535

Had the same problem. I was passing a non-const reference of custom class and the constructor complained (some tuple template errors). Replaced the reference with pointer and it worked.

Explanation (thanks @Holger Böhnke):

The reference must point to a copy-constructable object (copied when passing between threads) or use std::ref(yourParam) to explicitly request a shared reference.

Upvotes: 19

Timur
Timur

Reputation: 770

In my case I just changed the function name and error gone.

Before: thread(merge, first_item, mid_item, last_item).join();

After: thread(doMerge, first_item, mid_item, last_item).join();

And error gone. Yes it's freaking!!

Upvotes: 0

navaneeth mohan
navaneeth mohan

Reputation: 121

If your error message says

error: no matching constructor for initialization of 'std::thread'

then it's likely because you forgot to specify the C++ standard to be 11. For g++ compiler:

g++ std=c++11 main.cpp -o main

Upvotes: 0

aaronman
aaronman

Reputation: 18751

You literally just pass them in std::thread(func1,a,b,c,d); that should have compiled if the objects existed, but it is wrong for another reason. Since there is no object created you cannot join or detach the thread and the program will not work correctly. Since it is a temporary the destructor is immediately called, since the thread is not joined or detached yet std::terminate is called. You could std::join or std::detach it before the temp is destroyed, like std::thread(func1,a,b,c,d).join();//or detach .

This is how it should be done. 

std::thread t(func1,a,b,c,d);
t.join();

You could also detach the thread, read-up on threads if you don't know the difference between joining and detaching.

Upvotes: 97

pixelpax
pixelpax

Reputation: 1517

If you're getting this, you may have forgotten to put #include <thread> at the beginning of your file. OP's signature seems like it should work.

Upvotes: -3

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