Bug 53940

Summary: scanf(3) doesn't seem to handle %n properly
Product: [Retired] Red Hat Linux Reporter: Stas Sergeev <stssppnn>
Component: glibcAssignee: Jakub Jelinek <jakub>
Status: CLOSED NOTABUG QA Contact: Aaron Brown <abrown>
Severity: low Docs Contact:
Priority: medium    
Version: 7.1CC: fweimer
Target Milestone: ---   
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Hardware: i386   
OS: Linux   
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Fixed In Version: Doc Type: Bug Fix
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Last Closed: 2001-09-23 11:12:44 UTC Type: ---
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Description Flags
simple test program for scanf() none

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.