Check that we run from terminal. If no: restart in the default terminal.

run-in-terminal.cpp

#include <cstdlib>
#include <cstdio>
#include <iostream>
#include <vector>
#include <cstring>

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

using namespace std;

void check_terminal(int argc, char **argv)
{
    if (isatty(fileno(stdin)))
        return;

    // Run from GUI! Restart in terminal
    auto pid = fork();
    if (pid == 0) {
        std::vector<char*> args;
        args.reserve(argc + 2 + 1);

        // Try to run default terminal emulator. Fallback to xterm
        for (auto term : {"xdg-terminal", "x-terminal-emulator", "xterm", "rxvt"}) {
            args.insert(args.end(), {::strdup(term),
                                     ::strdup("-e")});

            // Dup my commad line options to the terminal
            for (int i = 0; i < argc; ++i)
                args.push_back(::strdup(argv[i]));

            args.push_back(nullptr);

            execvp(term, args.data());

            for (auto arg : args)
                free(arg); // strdup calls alloc
            args.clear();
        }
        // We should not be here
        exit(1);
    }
    // Parent process or fork-fail
    exit(pid < 0 ? 1 : 0);
}

bool check_gui()
{
    auto authority = getenv("XAUTHORITY");
    return authority && authority[0] ? true : false;
}

int main(int argc, char **argv)
{
    // Check running from the terminal. Re-run in terminal if required.
    check_terminal(argc, argv);

    // Ceck for GUI session
    auto gui = check_gui();

    // Regular execution
    cout << "Hello, from the terminal!\n";
    cout << "   is graphical session? " << (gui ? "yes!" : "no") << '\n';
    cin.get();

    return 0;
}