Fabrice Leal

cat /dev/random > /dev/null

Compile C++ code with C++11 threads

Consider the following code, which uses the C++11 (used to be known as C++0x) thread library:

#include <iostream>
#include <thread>

using namespace std;

void hello_world()
  cout << "Hello from thread!\n";

int main()
  thread t(hello_world);
  return 0;

How can we get this to work? If we compile it with:

g++ bare.cpp -o bare

We’ll get something like:

/usr/include/c++/4.5/bits/c++0x_warning.h:31:2: error: #error This file requires compiler and library support for the upcoming ISO C++ standard, C++0x. This support is currently experimental, and must be enabled with the -std=c++0x or -std=gnu++0x compiler options.

… and maybe something about the thread type used in the code:

error: ‘thread’ was not declared in this scope

So we add the std=c++0x

g++ bare.cpp -std=c++0x -o bare

No errors during compilation, but when we try to execute bare

$ ./bare
terminate called after throwing an instance of 'std::system_error'

… oops. We have to link this against the operating system’s implementation of threads. In linux, this is the libpthread library. The winning command is:

g++ bare.cpp -std=c++0x -lpthread -o bare

and then:

$ ./bare
Hello from thread!