将 output 打印到屏幕或给定文件名的选项（c++）

Question

I would like option 2 to pass the output to a typed file name. However, the program is creating the file but not passing the output to the file. I think just using ostream is fine here, but don't know how to go about it.

void displayTable(int n, char op) {
    int printOption;
    string outputFileName;
    ofstream createOutputFile;

    while (true) { //option for print screen or print to file
        cout << "Select: \n1) Print on Screen \n2) Print to a file name \nSelection: ";
        cin >> printOption;

        if (printOption == 1)
            break;
        else if (printOption == 2){
            cout << "Type in the name for the output file." << endl;
            cin >> outputFileName;
            createOutputFile.open(outputFileName);
            break;
        }
        else
            cout << "Please enter a valid number." << endl;
    }

    int max = getMaxSize(n, op);
    cout << setw(max) << op << "|";
    for (int i = 1; i <= n; ++i) {
        cout << setw(max) << i;
    }
    cout << endl;
    for (int i = 0; i < max; ++i) {
        cout << "-";
    }
    cout << "+";
    for (int i = 0; i < n * max; ++i) {
        cout << "-";
    }
    cout << endl;
    for (int i = 1; i <= n; ++i) {
        cout << setw(max) << i << "|";
        for (int j = 1; j <= n; ++j) {
            cout << setw(max) << getValue(i, j, op);
        }
        cout << endl;
    }

    cout << endl;
    createOutputFile.close();
}

Answer 1

You are not printing anything to createOutputFile , everything is being printed to cout instead. That is why to don't see anything in the file, and everything in the console.

The easiest way to solve your issue is to redirect cout to createOutputFile 's output buffer, eg:

auto cout_buff = cout.rdbuf();
...
createOutputFile.open(outputFileName);
cout.rdbuf(createOutputFile.rdbuf())
// all cout outputs will now go to the file...
...
cout.rdbuf(cout_buff); // restore when finished...

Otherwise, move your print logic to a separate function that takes an ostream& as a parameter:

void doMyLogic(ostream &os)
{
    // print to os as needed...
}

...

if (printOption == 1) {
    doMyLogic(cout);
    break;
} 
if (printOption == 2) {
    ...
    ofstream createOutputFile(outputFileName);
    doMyLogic(createOutputFile);
    break;
}
...