TITLE: (not) redirecting cin and cout

PROBLEM: Ejo Schrama <schrama@geo.tudelft.nl>

I couldn't find this in my C++ book, nor the FAQ's. Is it possible
to redirect text made by cout to a file (designed inside a c++
program) rather than standard output?


RESPONSE: clamage@Eng.Sun.COM (Steve Clamage), 30 Aug 95

There is no portable way to redirect cout (or cin) from within a program.
For one thing, cin/cout are not fstreams.

A simple way to get the effect you want is this:

int process(istream&, ostream&); // this function does all the work

main()
{
	istream *in = &cin;	// default to standard input
	ostream *out = &cout;	// default to standard output

	if( ... ) in = new ifstream(...);  // connect to file
	if( ! in  !! ! *in ) ... //report error

	if( ... ) out = new ofstream(...); // connect to file
	if( ! out || ! *out ) ... // report error

	int result = process(*in, *out); // do the work

	// clean up files if not cin/cout
	if( in != &cin )   delete in;
	if( out != &cout ) delete out;
	return result;
}

Function 'process' gets references to whatever the input and output streams
are, which could even be strstreams created in main, as a simple extension
to the above.