dup, dup2, and all that

[John E. Davis]

Hi,

I am writing a program that takes input from the user via stdin. In
addition, the program could take input from a file if stdin has been
redirected. I detect this using `isatty'. If the program has been started
as:

% ./a.out < input_file

after reading lines from the input file (redirected stdin), how do I redirect
stdin to what it was before redirection? This way I can take more input from
the user and any child processes will behave the same independent of whether I
typed:

% ./a.out
or
% ./a.out < input_file

I suspect it has something to do with dup, dup2, freopen, etc... but the man
pages are not too clear on this.

Thanks,
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