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From: bzs@bu-cs.BU.EDU (Barry Shein)
Newsgroups: comp.lang.c,comp.unix.wizards
Subject: Re: How to predict size of outcome of vsprintf?
Message-ID: <28874@bu-cs.BU.EDU>
Date: 21 Mar 89 19:26:00 GMT
References: <993@etnibsd.UUCP> <9872@smoke.BRL.MIL> <28831@bu-cs.BU.EDU> <1618@thor.acc.stolaf.edu> <9979@bloom-beacon.MIT.EDU>
Organization: Boston U. Comp. Sci.
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In-reply-to: scs@adam.pika.mit.edu's message of 21 Mar 89 04:15:41 GMT


Ok, there are two thoughts here:

	1. How to find out the number of characters a printf
	operation will generate.

	2. How to limit a printf operation to a buffer size.

I suggested the first might be the result of printing to a null
pointer (buffer or file.)

The second could be solved completely transparently by adding a format
effector which indicated the maximum buffer size ("must come first!")
Such as using %n# as in:

	sprintf(buf,"%80#%s",string);		/* 80 char buf including \0 */

or

	sprintf(buf,"%*#%s",BUFSIZ,string);	/* BUFSIZ char buf */

Not sure what "%n.m#" or "%#" might indicate (perhaps the latter would
just return a count of characters, ie, a zero length buffer?)

	-Barry Shein, Software Tool & Die