使用功能在cin和ifstream之间切换

Question

I am trying to manipulate an array with functions while switching between standard cin, cout and ifstream,ostream.

Specifically, I have an array of books and I have some basic functions like search title, publisher, price, etc. I also have 2 functions called "login" and "logout" to open a file and redirect bookList's istream and ostream to that outputfile when login, as well as close it and return back to istream, ostream when logout.

void bookList(istream& in, ostream& out)
{
    //ask for command from istream in
    //command selection loop
}

int load(ofstream& out, book booklist[], int size)
{
    //load list of books from input file
}

void logon(ofstream& out, string filename)
{
    out.open(filename.c_str());
}

void logoff(ofstream& out, string filename)
{
    out.close();
}
// some other functions

I also need to print out notification to the user (either onscreen when logged off or on file when logged on) whenever a function is called.

My tried to put ifstream& as a parameter in each functions, but they only print out to text file not on screen (because its just ifstream, not istream), but doing it the other way won't work.

My question is that is there method that can make function logon redirect istream of bookList to ifstream to the outputfile and vice versa for logoff? Rather than a "is-file-open" condition.

Answer 1

This may not be directly what your looking for but can be modified.

/// this buffer will be used to switch output
void IO_Switch(streambuf* buffer);

int main(){
    streambuf *buffer
    ofstream fout;
    fout.open("filename.txt");

    // below you call cout.rdbuf() which directs stream to cout
    IO_Switch(cout.rdbuf());
    cout << "This is coming to the console";
    // below you call fout.rdbuf());
    IO_Switch(fout.rdbuf());
    cout << "I used cout here, but the stream is redirected to fout ("filename.txt")

    return 0;
}

void IO_Switch(streambuf* buffer){
    cout.rdbuf(buffer);
}