CODEWITHSUNDEEP
c++c++11stream
RiaD
RiaD

Reputation: 47620

Choose fstream or cout depending on attributes

If there is argv[1] I want to put some data to new ofstream(argv[1]) i.e file with name argv[1]. But if there are no such argument I want to use cout instead.

I've tried 

std::ostream& output = argc >= 1 ? std::fstream(argv[0]) : std::cout;

But it even doesn't compile because of deleted constructor.

Upvotes: 3

Views: 418

Answers (3)

Ali
Ali

Reputation: 58471

Here is a truly C++11 solution:

ostream& out = [=]() -> ostream& {
    if (argc>1) {
        static fstream fs(argv[1]);
        return fs;
    }
    return cout;
}();

Upvotes: 3

Bo Persson
Bo Persson

Reputation: 92271

You cannot use a ternary operator with different types. The compiler cannot decide what type the result should have.

You could try

if (argc >= 1)
{
    std::fstream   Output(argv[0]);
    Process_data(Output);
}
else
    Process_data(std::cout);

Upvotes: 2

Kurt Stutsman
Kurt Stutsman

Reputation: 4034

You can create an fstream instance and delay opening it until necessary.

std::fstream file;
if (argc > 1)
    file.open(argv[1]);

std::ostream& output = argc > 1 ? file : std::cout;

Upvotes: 6

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