c++ unresolved identifier future - c++

Question

I was learning how to multithread in c++ and I run into this problem. I've searched the internet and didn't found a satisfactory answer.
I'm pretty sure the library's directory is included.
This are my system specifications:
Oracle Virtual box 5.2.12
Debian 9
Netbeans 8.2
gcc and g++ 6.3.0
This are the errors
Cannot find include file "/usr/include/c++/6".
unable to resolve identifier future.
unable to resolve identifier get.
This is my tutorials code:
// async example
#include <iostream> // std::cout
#include <future> // std::async, std::future
// a non-optimized way of checking for prime numbers:
bool is_prime (int x) {
std::cout << "Calculating. Please, wait...\n";
for (int i=2; i<x; ++i) if (x%i==0) return false;
return true;
}
int main ()
{
// call is_prime(313222313) asynchronously:
std::future<bool> fut = std::async (is_prime,313222313);
std::cout << "Checking whether 313222313 is prime.\n";
// ...
bool ret = fut.get(); // waits for is_prime to return
if (ret) std::cout << "It is prime!\n";
else std::cout << "It is not prime.\n";
return 0;
}
And this is the building output:
cd '/home/sulheru/NetBeansProjects/20180907/asyncTutorial'
/usr/bin/make -f Makefile CONF=Debug
"/usr/bin/make" -f nbproject/Makefile-Debug.mk QMAKE= SUBPROJECTS= .build-conf
make[1]: se entra en el directorio '/home/sulheru/NetBeansProjects/20180907/asyncTutorial'
"/usr/bin/make" -f nbproject/Makefile-Debug.mk dist/Debug/GNU-Linux/asynctutorial
make[2]: se entra en el directorio '/home/sulheru/NetBeansProjects/20180907/asyncTutorial'
mkdir -p build/Debug/GNU-Linux
rm -f "build/Debug/GNU-Linux/main.o.d"
g++ -c -g -include /usr/include/c++/6.3.0 -MMD -MP -MF "build/Debug/GNU-Linux/main.o.d" -o build/Debug/GNU-Linux/main.o main.cpp
cc1plus: fatal error: /usr/include/c++/6.3.0: No existe el fichero o el directorio
compilation terminated.
nbproject/Makefile-Debug.mk:66: fallo en las instrucciones para el objetivo 'build/Debug/GNU-Linux/main.o'
make[2]: *** [build/Debug/GNU-Linux/main.o] Error 1
make[2]: se sale del directorio '/home/sulheru/NetBeansProjects/20180907/asyncTutorial'
nbproject/Makefile-Debug.mk:59: fallo en las instrucciones para el objetivo '.build-conf'
make[1]: *** [.build-conf] Error 2
make[1]: se sale del directorio '/home/sulheru/NetBeansProjects/20180907/asyncTutorial'
nbproject/Makefile-impl.mk:39: fallo en las instrucciones para el objetivo '.build-impl'
make: *** [.build-impl] Error 2
BUILD FAILED (exit value 2, total time: 323ms)

Answer 1

You need the -pthread option in your compiler flags.
Example:
➜ g++ -std=c++11 -pthread async.cpp
➜ ./a.out
Checking whether 313222313 is prime.
Calculating. Please, wait...
It is prime!