NetBSD Problem Report #345

From gnats  Tue Jul 19 00:36:53 1994
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Date: Tue, 19 Jul 1994 00:40:50 -0700
From: banshee@gabriella.resort.com (Robert Dobbs)
Reply-To: banshee@gabriella.resort.com
To: gnats-bugs@sun-lamp.cs.berkeley.edu
Subject: i386 ftruncate() error
X-Send-Pr-Version: 3.2

>Number:         345
>Category:       lib
>Synopsis:       ftruncate() fails in several scenarios
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    gnats-admin
>State:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Jul 19 00:50:04 +0000 1994
>Closed-Date:    Wed Jul 20 07:16:40 +0000 1994
>Last-Modified:  
>Originator:     Robert Dobbs
>Release:        supped -current
>Organization:
"Church of the Subgenius"
>Environment:
i386 DX/25, netbsd-current, libc
System: NetBSD gabriella.resort.com 1.0-ALPHA NetBSD 1.0-ALPHA (BANSHEE) #0: Mon Jul 11 22:25:01 PDT 1994 banshee@cooltech.resort.com:/usr/src/sys/arch/i386/compile/BANSHEE i386


>Description:
	ftruncate(fileno(fp),0) fails to truncate the file referenced by
	fp if:
		fp has been written to with fprintf()
		fp was opened in "a" or "r+" mode
	Always returns -1 and sets errno, even in the "w" no write case
	where it truncates the file.
>How-To-Repeat:

/* make ftruncate fail */
#include <stdio.h>
#include <errno.h>
extern int errno;

main()
{
        FILE *fp;

        fp = fopen("foo","w");
/* comment out fprintf line to make ftruncate work
   but it still returns -1 and sets errno. */
        fprintf(fp,"Mom loves you");
printf("%d\n", errno);
printf("trunc: %d\n",ftruncate(fileno(fp),10));
printf("%d\n", errno);
        fflush(fp);
}


>Fix:
	This is a bug in the supplied program.  The second argument to
	ftruncate() must be an off_t.  Therea are several ways to accomplish
	this:

		* Have a prototype for ftruncate() in scope.
		* Cast the argument to off_t explicitly.
		* Use a variable or expression which evaluates to an off_t.

	At any rate, the supplied program is in error.  This is not a bug in
	NetBSD.  - mycroft

>Release-Note:
>Audit-Trail:
State-Changed-From-To: open->closed 
State-Changed-By: mycroft 
State-Changed-When: Wed Jul 20 00:16:40 PDT 1994 
State-Changed-Why:  
This is not a bug in NetBSD; it is a bug in the supplied program. 
>Unformatted:

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