C++ threads not matching function call with std::vector as argument

Question

I'm trying to write a program that executes Quicksort using two threads (one for a partition and one for another). The important code looks like this:

// Function that makes the partitions
size_t Divide(std::vector<int> &v, size_t ini, size_t fin){
   // Not so important code...
}

// Function called by threads
void QuickSort(std::vector<int> &v, size_t ini, size_t fin){
   // Not so important code...
}

// Initial partition
void QuickSort(std::vector<int> &v){
   size_t division = Divide(v, 0, v.size());

   std::thread p1(QuickSort, std::ref(v), 0, division);
   std::thread p2(QuickSort, std::ref(v), division+1, v.size());

   p1.join();
   p2.join();
}

I get this error by the compiler, which I can't fully understand:

thrtest.cpp: In function ‘void QuickSort(std::vector<int>&)’:
thrtest.cpp:57:54: error: no matching function for call to ‘std::thread::thread(<unresolved overloaded function type>, std::reference_wrapper<std::vector<int> >, int, size_t&)’
std::thread p1(QuickSort, std::ref(v), 0, division);
                                                  ^
In file included from thrtest.cpp:7:0:
/usr/include/c++/5/thread:133:7: note: candidate: template<class _Callable, class ... _Args> std::thread::thread(_Callable&&, _Args&& ...)
   thread(_Callable&& __f, _Args&&... __args)
   ^
/usr/include/c++/5/thread:133:7: note:   template argument deduction/substitution failed:
thrtest.cpp:57:54: note:   couldn't deduce template parameter ‘_Callable’
std::thread p1(QuickSort, std::ref(v), 0, division);
                                                  ^
In file included from thrtest.cpp:7:0:
/usr/include/c++/5/thread:128:5: note: candidate: std::thread::thread(std::thread&&)
 thread(thread&& __t) noexcept
 ^
/usr/include/c++/5/thread:128:5: note:   candidate expects 1 argument, 4 provided
/usr/include/c++/5/thread:122:5: note: candidate: std::thread::thread()
 thread() noexcept = default;
 ^
/usr/include/c++/5/thread:122:5: note:   candidate expects 0 arguments, 4 provided
thrtest.cpp:58:63: error: no matching function for call to ‘std::thread::thread(<unresolved overloaded function type>, std::reference_wrapper<std::vector<int> >, size_t, std::vector<int>::size_type)’
std::thread p2(QuickSort, std::ref(v), division+1, v.size());
                                                           ^
In file included from thrtest.cpp:7:0:
/usr/include/c++/5/thread:133:7: note: candidate: template<class _Callable, class ... _Args> std::thread::thread(_Callable&&, _Args&& ...)
   thread(_Callable&& __f, _Args&&... __args)
   ^
/usr/include/c++/5/thread:133:7: note:   template argument deduction/substitution failed:
thrtest.cpp:58:63: note:   couldn't deduce template parameter ‘_Callable’
std::thread p2(QuickSort, std::ref(v), division+1, v.size());
                                                           ^
In file included from thrtest.cpp:7:0:
/usr/include/c++/5/thread:128:5: note: candidate: std::thread::thread(std::thread&&)
 thread(thread&& __t) noexcept
 ^
/usr/include/c++/5/thread:128:5: note:   candidate expects 1 argument, 4 provided
/usr/include/c++/5/thread:122:5: note: candidate: std::thread::thread()
 thread() noexcept = default;
 ^
/usr/include/c++/5/thread:122:5: note:   candidate expects 0 arguments, 4 
provided

Compilation is g++ -g -O2 -std=c++14 thrtest.cpp -o thrtest

I looked through many posts and tried many things to solve this, but I must be getting something wrong.

Well, I thought there was no problem in overloading the function (the first definition has different arguments), but I tried different names and it gives another, more cryptic, error... — Francisco Gallego Salido, May 12 '17 at 01:17
I don't believe that's the problem but it just makes it a bit more confusing while trying to figure it out. — Eli Sadoff, May 12 '17 at 01:18

score 0 · Answer 1 · answered May 12 '17 at 01:22

0

QuickSort is an overloaded function, you have to cast it:

auto quick_sort = static_cast<void (*)(std::vector<int> &, size_t, size_t)>(QuickSort);
std::thread p1(quick_sort, std::ref(v), 0, division);
std::thread p2(quick_sort, std::ref(v), division+1, v.size());

answered May 12 '17 at 01:22

O'Neil

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Or just give the two functions different names. – 1201ProgramAlarm May 12 '17 at 01:23
I was about to answer my question because I managed to solve it (in a different way). It seems that adding `-lpthread` to compilation options and changing the name of the functions works, but not just changing the names. – Francisco Gallego Salido May 12 '17 at 01:27

C++ threads not matching function call with std::vector as argument

1 Answers1