CODEWITHSUNDEEP
c++multithreadingclang
user9564469
user9564469

Reputation: 21

The program compiles using Visual Studio but clang and gcc cannot do it

Here's my code:

#include <iostream>
#include <future>
#include <thread>
#include <vector>

using namespace std;

vector <int> exec(vector <int> &a, vector <int> &b) {
vector <int> res = a;
res.push_back(b[0]);
res.push_back(b[1]);
res.push_back(b[2]);
res.push_back(b[3]);
return res;
}


int main() {


vector <int> a1{ 1, 2, 3, 4 }, a2{ 5, 6, 7 , 8  };

std::packaged_task<vector <int>(vector <int>, vector <int>)> task(exec);
std::future<vector <int>> ret = task.get_future();            
std::thread th(std::move(task), a1, a2);  

th.detach();

vector <int> P1 = ret.get();


for (auto i = 0; i < P1.size(); ++i) {
    cout << P1[i];
}
cout << endl;


system("pause");
return 0;
}

Using -std=c++17 or -std=c++14 Clang always throws me one error:

In file included from Source.cpp:2:
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\future:568:6: error: no
matching constructor for initialization of 'function<std::vector<int,
std::allocator<int> > (std::vector<int, std::allocator<int> >, std::vector<int,
std::allocator<int> >)>'
: _Fn(_Fnarg)
  ^   ~~~~~~

And it also throws me a couple of warnings. The same thing goes for g++. I use Visual Studio 2015 and clang 6.0.0. What's the matter?

Upvotes: 1

Views: 49

Answers (2)

SergeyA
SergeyA

Reputation: 62613

You need packaged_task types match function types. In particular, since I assume you'd like to keep references for exec:

std::packaged_task<vector<int> (vector<int>&, vector<int>&)> task(exec);
std::future<vector <int>> ret = task.get_future();            
std::thread th(std::move(task), std::ref(a1), std::ref(a2));

Upvotes: 1

YSC
YSC

Reputation: 40150

Your exec function takes references to vectors, but you define your task and future with an underlying function taking vector's copies. Either change exec or task definition.

I'd advise changing exec type to:

std::vector<int> exec(std::vector<int> base, std::vector<int> const &b) {
    base.push_back(b[0]);
    base.push_back(b[1]);
    base.push_back(b[2]);
    base.push_back(b[3]);
    return base;
}

and task to:

std::packaged_task<std::vector<int>(std::vector<int>, std::vector<int> const&)> task(exec);

Upvotes: 0

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