在C ++中，有没有一种可移植的方法将stdin重定向到字符串？

Question

Is it possible in C++ to redirect stdin to string in C++?

Using freopen I can redirect stdin to file, so both scanf and cin will use a content of that file. Using manipulations with stringstream and cin.rdbuf() I can redirect cin to that string, so any call to cin will work with my string. BUT scanf will continue to work with previous input stream. I guess it is possible to do with Unix's pipes but it's not available under Windows.

Is it possible to solve this in a portable way?

Answer 1

This isn't the best way to do it, but you can make it work with something like this:

// warning - has side effects (sets noskipws) but we don't care (its an example)
ostream& operator<< (ostream& out, istream& in)
{
    in >> noskipws;
    char c;
    in >> c;

    while (in)
    {
        out << c;
        in >> c;
    }

    return out;
}

int main()
{
    ostringstream inputstr;
    inputstr << cin;

    inputstr.str(); // contains all data from stdin
    return;
}

Answer 2

Assuming both the C and C++ standard streams are synchronized, the following should work:

class save_buffer
{
public:
    save_buffer(std::ios& str) :
        my_str(str),
        m_sbuf(str.rdbuf())
    { }

    ~save_buffer()
    {
        m_str.rdbuf(m_sbuf);
    }
private:
    std::ios& m_str;
    std::streambuf* m_sbuf;
};

int main()
{
    std::istringstream buf;

    save_buffer sb(std::cin);
    std::cin.rdbuf(buf.rdbuf());
}