Does the C++ standard support processes?

Boost started supporting processes in version 1.64.0 (April 2017).

https://www.boost.org/doc/libs/1_70_0/doc/html/process.html

The fact that it is a Boost feature is a source of hope for its inclusion in a future C++ standard.

No, the c++ standard (particularly C++11) doesn't have any notion of a process (hence I can't give you a more reasonable reference here as a search result from the most popular and currently most up to date c++ documentation site).

I'm also not aware that process support is planned for the next standard version C++-17 (aka C++-1z). At least the Wikipedia Site doesn't mention it.

There is a popular implementation that was proposed for boost, but that never was drawn for a C++ standard proposal.

You usually can't write portable code to run on bare metal systems, where only one process exists.

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However, is there a way to execute the bar() function in a separate process?

The simplest option to do that is to fallback to fork() and wait() as specified by the POSIX Open Group:

#include <iostream>
#include <unistd.h>
#include <sys/wait.h>

void bar()
{
    std::cout << "bar()\n";
}    

int main(int argc, char **argv)
{
    pid_t pid = fork();

    if (pid == 0)
    {
        // child process
        bar();
    }
    else if (pid > 0)
    {
        // parent process
        wait(NULL);    
    }
    else
    {
        // fork failed
        std::cerr << "fork() failed!" << std::endl;
        return 1;
    }


    return 0;
}

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Though I don't see much of a point to create an extra process to execute a simple function. Creating a process creates a lot of overhead you don't want in such case.

Well, if you want to start another program using functions from the exec() function family that's a different use case.

I'd recommend sticking to std::threads for your example.