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How should I read from a file if there is one given as a command line argument, if not I would like to read from std::cin. I tried to solve this with pointers to istrem, but is there a better way.

Igracx33
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    1) "_I tried to solve this with pointers to istrem_" Why would you need to use pointers to `std::ifstream`? 2) Please show [mcve] with an actual question. SO is **not** code writing service. – Algirdas Preidžius Jul 23 '18 at 13:01
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    @DevSolar Does not look like a duplicate. – zdf Jul 23 '18 at 13:38

3 Answers3

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You probably tried to use a pointer to istream to have it point to either an std::fstream instance or to std::cin depending on the command line parameters.

It would be better as a reference:

int main(int argc, char *argv[])
{
    std::fstream fin;

    if (argc > 1)
        fin.open(argv[1]);

    std::istream &in = fin.is_open() ? fin : std::cin;

    // ... continue using `in`
}
acraig5075
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0

ifstream derives from istream. So if a file is given on the command line then you open the file and use the resulting ifstream as istream. Otherwise you use std::cin.

Goswin von Brederlow
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Check this : How do you open a file in C++?

With the exception that path_to_file is an input coming from std::cin or command line argument.

Domenico Paolicelli
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  • If the answer to the question, is present in another SO question, one should flag as duplicate, **not** to post his own answer linking to another one.. – Algirdas Preidžius Jul 23 '18 at 13:06