Question

Problematic code:

#include <array>
#include <iostream>
#include <cstring>

int main(int argc, char *argv[])
{
    using namespace std;

    cout << "Read from file:" << endl;

    while (!cin.eof())
    {
        array<char, 16> l_array;
        cin.read(l_array.data(), l_array.size());
        cout.write(l_array.data(), cin.gcount());
    }

    cout << endl;
    cout << "Read from keyboard:" << endl;

    cin.rdbuf(cout.rdbuf());

    while (!cin.eof())
    {
        array<char, 64> l_array;
        memset(l_array.data(), 0, l_array.size());
        cin.read(l_array.data(), l_array.size());

        cout << "===== DATA =====" << endl;
        cout << l_array.data() << endl;
        cout << "================" << endl;
    }
}

This is how i run my program:

./application < file.txt

I can read data from pipe without problems but when i want to read it again it is still asociated with pipe. I have no idea how to switch it back. I have found ‘rdbuf’ function which can change it, but I have no idea how to use it.

I only found examples when you stard with keyboard switch to file and back to keyboard.

Like here: http://www.cplusplus.com/reference/iostream/ios/rdbuf/

But i don’t have streambuf remembered so I can’t do it like they did. I want to write program which can read most of data from file, and ask only when something is missing or just to ask user in runtime about permision or something. All inside console under linux.

@EDIT
Thank you for help, I post solution

class RedirectCinToConsole
{
    protected:
        std::ifstream m_console;
        std::streambuf *m_oldCin;
        bool m_success;

    public:
        RedirectCinToConsole() :
            m_oldCin(0),
            m_success(false)
        {
            m_console.open("/dev/tty");

            if (m_console.is_open())
            {
                m_success = true;
                m_oldCin = std::cin.rdbuf(m_console.rdbuf());
            }
        }
        virtual ~RedirectCinToConsole()
        {
            if (m_oldCin)
            {
                std::cin.rdbuf(m_oldCin);
            }
            m_console.close();
        }

        operator bool () const { return m_success; }
};

int main()
{
    RedirectCinToConsole l_redirect;
    if (l_redirect)
    {
        std::string l_helloWorld;
        std::cin >> l_helloWorld;
        std::cin.ignore();

        std::cout << l_helloWorld;
    }
    return 0;
}

Answer 1

Try opening /dev/tty. This will be your process’s associated console, if there is any. If your process was started from a daemon, it could fail.