Bug 53940 - scanf(3) doesn't seem to handle %n properly
Summary: scanf(3) doesn't seem to handle %n properly
Keywords:
Status: CLOSED NOTABUG
Alias: None
Product: Red Hat Linux
Classification: Retired
Component: glibc
Version: 7.1
Hardware: i386
OS: Linux
medium
low
Target Milestone: ---
Assignee: Jakub Jelinek
QA Contact: Aaron Brown
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2001-09-23 11:10 UTC by Stas Sergeev
Modified: 2016-11-24 14:47 UTC (History)
1 user (show)

Fixed In Version:
Clone Of:
Environment:
Last Closed: 2001-09-23 11:12:44 UTC
Embargoed:


Attachments (Terms of Use)
simple test program for scanf() (203 bytes, patch)
2001-09-23 11:12 UTC, Stas Sergeev
no flags Details | Diff

Description Stas Sergeev 2001-09-23 11:10:25 UTC
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 11:12:40 UTC
Created attachment 32418 [details]
simple test program for scanf()

Comment 2 Jakub Jelinek 2001-09-24 09:15:42 UTC
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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