Question

I’m new to the mac and trying to get gcc 4.6 working.

I installed MacPorts and installed gcc 4.6.1 (by executing sudo port install gcc46). I’m trying to compile a simple test code that compiles fine on Linux (with gcc 4.6.1 and 4.6.2) and Windows, but I’m getting errors that make me thing there is something wrong with the installed libraries.

#include <iostream>
#include <type_traits>
#include <future>

struct test {
    void get() {}
};

/*template<typename Func>
test async(const Func &f) {
    f();
    return test();
}*/

using namespace std;

int main (int argc, const char * argv[])
{
    auto t1 = async([]() -> int{
        cout << "This is thread 1" << endl;
        return 1;
    });

    auto t2 = async([]() -> int {
        cout << "This is thread 2" << endl;
        return 2;
    });

    std::cout << "This is the main thread" << endl;

    t1.get();
    t2.get();

    return 0;
}

The error messages:

macbook01:Test fozi$ g++ main.cpp -o test -std=c++0x
main.cpp: In function 'int main(int, const char**)':
main.cpp:30:6: error: invalid use of incomplete type 'std::enable_if<true, std::future<int> >::type'
/opt/local/include/gcc46/c++/future:111:11: error: declaration of 'std::enable_if<true, std::future<int> >::type'
main.cpp:30:6: error: unable to deduce 'auto' from '<expression error>'
main.cpp:35:6: error: invalid use of incomplete type 'std::enable_if<true, std::future<int> >::type'
/opt/local/include/gcc46/c++/future:111:11: error: declaration of 'std::enable_if<true, std::future<int> >::type'
main.cpp:35:6: error: unable to deduce 'auto' from '<expression error>'
/opt/local/include/gcc46/c++/future: At global scope:
/opt/local/include/gcc46/c++/future:150:5: error: 'typename std::enable_if<(! std::is_same<typename std::decay<_Functor>::type, std::launch>::value), std::future<decltype (declval<_Fn>()((declval<_Args>)()...))> >::type std::async(_Fn&&, _Args&& ...) [with _Fn = main(int, const char**)::<lambda()>, _Args = {}, typename std::enable_if<(! std::is_same<typename std::decay<_Functor>::type, std::launch>::value), std::future<decltype (declval<_Fn>()((declval<_Args>)()...))> >::type = std::future<int>]', declared using local type 'main(int, const char**)::<lambda()>', is used but never defined [-fpermissive]
/opt/local/include/gcc46/c++/future:150:5: error: 'typename std::enable_if<(! std::is_same<typename std::decay<_Functor>::type, std::launch>::value), std::future<decltype (declval<_Fn>()((declval<_Args>)()...))> >::type std::async(_Fn&&, _Args&& ...) [with _Fn = main(int, const char**)::<lambda()>, _Args = {}, typename std::enable_if<(! std::is_same<typename std::decay<_Functor>::type, std::launch>::value), std::future<decltype (declval<_Fn>()((declval<_Args>)()...))> >::type = std::future<int>]', declared using local type 'main(int, const char**)::<lambda()>', is used but never defined [-fpermissive]

Note that if I use my dummy async function it compiles and runs fine.

I’m kind of stuck, do I have to install a specific library (version)? How do I do that?

Answer 1

We’re getting there

gcc 4.7 (port) compiles this code just fine.

Xcode 4.3 comes with clang 3.1 which is supposed to support this, but it crashes when I try to compile. However I built clang from SVN and replaced the compiler Xcode is using and now it compiles and runs fine as well.

And it only took half a year.