compressed files

[Robert Skinner]

In article <3339 at uceng.UC.EDU>, trohling at uceng.UC.EDU (tom rohling) writes:
> 
>      Can a compressed file be accessed through fortran (or C) much in the 
> same way that 'zcat' uncompresses the file to std out but leaves the file 
> in its compressed state?  i.e. can I read the contents of a compressed file
> from a program without having to uncompress it first?  Sort of like zcat 
> it into ram....

You can use popen to get a file pointer to the output of zcat.  This acts 
just like fopen, but if the file isn't there, it looks for the compressed
version (with the .Z extension) and makes a pipe that zcat's it into
your program.

	#include	<stdio.h>
	#include	<errno.h>

	FILE	*zopen( name )
	char	*name;
	{
		FILE	*fp;
		char	cmd[256];

		errno = 0;
		fp = fopen( name, "r" );

		if( !fp && errno == 0 ) { 	/* file doesn't exist */
			sprintf( cmd, "zcat %s.Z" );
			fp = popen( cmd, "r" );
		}

		return fp;
	}

(No, this isn't debugged, and I should check whether the compressed
file is there, but you get the idea.)  One drawback is that you can't 
seek on it.  

I think you lose if you HAVE to seek on the file.  Seeking is very tricky
when a (de)compression scheme is involved.

good luck,
Robert Skinner
robert at sgi.com

		Which is worse, ignorance or apathy?
		Who knows?  Who cares?