Bug 53940 – scanf(3) doesn't seem to handle %n properly

Bug 53940 - scanf(3) doesn't seem to handle %n properly

Summary:	scanf(3) doesn't seem to handle %n properly

Status:	CLOSED NOTABUG

Aliases:	None

Product:	Red Hat Linux
Classification:	Retired
Component:	glibc (Show other bugs)
Sub Component:
Version:	7.1
Hardware:	i386 Linux

Priority	medium Severity low
Target Milestone:	---
Target Release:	---
Assigned To:	Jakub Jelinek
QA Contact:	Aaron Brown
Docs Contact:

URL:
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Depends On:
Blocks:
	Show dependency tree / graph

Reported:	2001-09-23 07:10 EDT by Stas Sergeev
Modified:	2016-11-24 09:47 EST (History)
CC List:	1 user (show)

See Also:
Fixed In Version:
Doc Type:	Bug Fix
Doc Text:
Story Points:	---
Clone Of:
Environment:
Last Closed:	2001-09-23 07:12:44 EDT
Type:	---
Regression:	---
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Documentation:	---
CRM:
Verified Versions:
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oVirt Team:	---
RHEL 7.3 requirements from Atomic Host:
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Attachments	(Terms of Use)
simple test program for scanf() (203 bytes, patch) 2001-09-23 07:12 EDT, Stas Sergeev	no flags	Details \| Diff
Add an attachment (proposed patch, testcase, etc.)

Groups: None (edit)

Description Stas Sergeev 2001-09-23 07:10:25 EDT

From Bugzilla Helper:
User-Agent: Mozilla/4.76 [en] (X11; U; Linux 2.2.19 i686)

Description of problem:
If scanf() reads no symbols, it ignores %n

Version-Release number of selected component (if applicable):
all versions.

How reproducible:
Always

Steps to Reproduce:
1. Compile the test program (attached)
2. run it

	

Actual Results:  10 3

Expected Results:  0 3

Additional info:

Not shure that it is a bug, but I have one program that crashes due
to this strange behavior.

Comment 1 Stas Sergeev 2001-09-23 07:12:40 EDT

Created attachment 32418 [details]
simple test program for scanf()

Comment 2 Jakub Jelinek 2001-09-24 05:15:42 EDT

It is a bug, but not in glibc, but in the program you have.
In first sscanf, you get matching failure already before the %n directive,
so it is not assigned. See e.g. ISO C99, or
http://www.opengroup.org/onlinepubs/007908799/xsh/fscanf.html
You really have to check *scanf return value first before assuming which
arguments were assigned to.

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