CODEWITHSUNDEEP
c++multithreadingboostboost-thread
Pietro
Pietro

Reputation: 13164

How can I get a value back from a boost::thread?

Trying this with boost::thread:

void MyClass::Func(int a, int b, int c, int &r) {
    r = a + b + c;
}

void MyClass::Func2(int a, int b, int c) {
    memberVar = a + b + c;
}

void MyClass::Work()
{
    int a = 1, b = 2, c = 3;
    int r;
    boost::thread_group tg;

    for(int i = 0; i < 10; ++j)
    {
        boost::thread *th = new boost::thread(Func, a, b, c, r);    //* error

        tg.add_thread(th);
    }

    tg.join_all();
}

1) I get this error on line //* of which I cannot find the reason:

error: expected primary-expression before ',' token

2) Is a reference parameter (r) a good way to get a value back from a thread? Or should I do like in Func2(), setting a member variable? (taking care of who wrote what)

3) Once I put a thread in a thread_group, how can I get values back from it? I cannot use the original pointer any more...

Thank you.

Upvotes: 1

Views: 167

Answers (1)

thomas
thomas

Reputation: 525

#include <boost/thread/thread.hpp>
#include <boost/bind.hpp> 

using namespace std;

class MyClass{
public:
    void Func(int a, int b, int c, int &r) { r = a + b + c; }

    void Work()
    {
        using namespace boost;

        int a = 1, b = 2, c = 3;
        int r=0;

        thread_group tg;

        for(int i = 0; i < 10; ++i){
            thread *th = new thread(bind(&MyClass::Func,this,a, b, c, r));  
            tg.add_thread(th);

        }

        tg.join_all();
    }
};

void main(){
     MyClass a;
     a.Work();
}

Upvotes: 2

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