CODEWITHSUNDEEP
c++boostboost-process
zack evein
zack evein

Reputation: 289

Create child process with custom environment using boost

The documentation boost doesn't provide any example for creating a child process with a custom environment using process::child(...).
An example is given with process::system(...) but the function system has less possible operations (such as pipes or waitpid) so I would like to have a full example using process::child if possible.

Upvotes: 6

Views: 4342

Answers (2)

Serge Grondin
Serge Grondin

Reputation: 71

The last answer and comment are quite old but I can confirm that boost::process::child with environment parameter works using Boost version 1.65 under Ubuntu 18.04. The documentation about that is quite thin, so I had to find out by myself:

std::string command = "/usr/bin/something";
ipstream pipe_stream;

// Get current env
auto env = boost::this_process::environment();
// Add something
env["CHINESE_FOOD"] = "GOOD";
// Change something
env["CHINESE_FOOD"] = "GREAT";
// Delete something
env["CHINESE_FOOD"].clear();

boost::process::child childProc(command, env, std_out > pipe_stream);

And of course, if environment is not needed, it will inherit from parent process automatically

std::string command = "/usr/bin/something";
ipstream pipe_stream;

boost::process::child childProc(command, std_out > pipe_stream);

Upvotes: 6

xaxxon
xaxxon

Reputation: 19771

in system.hpp, system_impl, which supports custom env, is implemented in terms of child, 

template<typename IoService, typename ...Args>
inline int system_impl(
        std::true_type, /*needs ios*/
        std::true_type, /*has io_context*/
        Args && ...args)
{
    IoService & ios = ::boost::process::detail::get_io_context_var(args...);

    system_impl_success_check check;

    std::atomic_bool exited{false};

    child c(std::forward<Args>(args)...,
            check,
            ::boost::process::on_exit(
                [&](int, const std::error_code&)
                {
                    ios.post([&]{exited.store(true);});
                }));
    if (!c.valid() || !check.succeeded)
        return -1;

    while (!exited.load())
        ios.poll();

    return c.exit_code();
}

So the call to system from the docs: 

bp::system("stuff", bp::env["VALUE_1"]="foo", bp::env["VALUE_2"]+={"bar1", "bar2"});

which calls:

template<typename ...Args>
inline int system(Args && ...args)
{
    typedef typename ::boost::process::detail::needs_io_context<Args...>::type
            need_ios;
    typedef typename ::boost::process::detail::has_io_context<Args...>::type
            has_ios;
    return ::boost::process::detail::system_impl<boost::asio::io_context>(
            need_ios(), has_ios(),
            std::forward<Args>(args)...);
}

translates into this function, so you should be able to do the same.

Upvotes: 0

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