File descriptors and streams and co

[hamilton at osiris.cso.uiuc.edu]

rds95 at leah.Albany.Edu says:

> I want to be able to make "stdin" read from someplace besides, well,
> standard input in the middle of my program, and then go back to where
> it was again.

i would do it like this:

	void fexchange(a, b)
	FILE *a;
	FILE *b;
	{
		FILE tmp;

		tmp = *a;
		*a = *b;
		*b = tmp;
	}

	FILE *my_file;

	/* open my_file */

	/* exchange stdin & my_file */
	fexchange(stdin, my_file);

	/* ... use stdin ... */

	/* restore stdin */
	fexchange(stdin, my_file);

	fclose(my_file);

i've been using this technique for years in an application where i
wanted a nested "#include" capability for interactive input.

	wayne hamilton
	U of Il and US Army Corps of Engineers CERL
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