std::thread calling template function out of template function

Question

I am trying to create threads out of a template function giving the thread another template function.

I have appended an expample of the situation that gives the same errors. Giving the thread a function that is not templated (ie here one with int and one with float) does not result in an error. However since I plan to use this function with many different types I don't want to specify the template types. Also I have tried several specifyings of the template type (eg std::thread<T> or std::thread(function<T>) without any success.

Question: How can I call a template function with a std:thread out of a template function?

The following is a minimum compiling example of the situation, in reality the templates are own classes:

#include <thread>
#include <string>
#include <iostream>

template<class T>
void print(T* value, std::string text)
{
   std::cout << "value: " << *value << std::endl;
   std::cout << text << std::endl;
}

template<class T>
void threadPool(T* value)
{
   std::string text = "this is a text with " + std::to_string(*value);
   std::thread(&print, value, text);
}

int main(void)
{
   unsigned int a = 1;
   float b = 2.5;
   threadPool<unsigned int>(&a);
   threadPool<float>(&b);
}

compiling this example with g++ or icc with:

icc  -Wall -g3 -std=c++11 -O0 -pthread

gives the folowing error messages (icc):

test.cpp(17): error: no instance of constructor "std::thread::thread" matches the argument list
        argument types are: (<unknown-type>, unsigned int *, std::string)
    std::thread(&print, value, text);
    ^
      detected during instantiation of "void threadPool(T *) [with T=unsigned int]" at line 24

test.cpp(17): error: no instance of constructor "std::thread::thread" matches the argument list
        argument types are: (<unknown-type>, float *, std::string)
    std::thread(&print, value, text);
    ^
      detected during instantiation of "void threadPool(T *) [with T=float]" at line 25

compilation aborted for test.cpp (code 2)

Thank you very much in advance

Answer 1

That's because just print is not a complete type.

I haven't tried it, but doing e.g. &print<T> should work.

---

Unrelated, but there's no need to pass pointers to your threadPool function. Passing a (possible constant) reference would probably be better.

Answer 2

Use this:

template<class T>
void threadPool(T* value)
{
   std::string text = "this is a text with " + std::to_string(*value);
   std::thread(&print<T>, value, text);
}

Answer 3

Try

std::thread([value,text]() { print(value, text); });