Redirecting standard IO

[BiK]

Could you tell me how to use the ONLINE_JUDGE symbol in C++ in order to test my program using file input and file output. In other words I need the C++ equivallent code of the following C code:

[c]

#ifndef ONLINE_JUDGE
close (0); open ("myprog.in", O_RDONLY);
close (1); open ("myprog.out", O_WRONLY | O_CREAT, 0600);
#endif
[/c]

[Subeen]

you can use the freopen() function to test your programs.

[Ivor]

I'm usually running my programs from command-line giving file as input stream:

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progname <inputfile

It works in win/dos, if I'm correct it will work on linux too.
Ivor

[Krzysztof Duleba]

It works with Linux as well. It's a surprise - I always used

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cat input|progname

but your form is shorter, so I'm going to switch

[Ivor]

i discovered that a couple of days ago. I needed to dump the program output to a file, and as I'm not a linux user I just tried '>filename'... it worked, so I supposed '<filename' would also work. good to hear it works

[BiK]

Hi Subeen. You mean to replace the open function with freopen or what? Could you type the actual C++ code. I know nothing about freopen. And I want to run my programs under Windows.

[Subeen]

here is it:
for reading from file:

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freopen("input file name", "rt", stdin);

and for writing in file:

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freopen("output file name", "wt", stdout);

just add these two lines before ur program ( in main method )

[Per]

That would still be the C way of doing it. If you're using C++ iostreams, you can write like this (though there may be a simpler way?):

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#include <fstream>

cin.rdbuf((new ifstream("___.in"))->rdbuf());
cout.rdbuf((new ofstream("___.out"))->rdbuf());

(And as long as it's for programming contest purposes, there's no reason to worry about freeing the created streams in the end.)

But I say I definitely recommend doing it Ivors way, redirecting the I/O from/to file with "<" and ">". That way you don't have to clutter up your code more than necessary.

[BiK]

Thanks guys. Now everything is OK.

[macin]

my flavor:

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std::filebuf in, out;
std::cin.rdbuf(in.open("stdin.txt", std::ios_base::in));
std::cout.rdbuf(out.open("stdout.txt", std::ios_base::out));