Issue 0014.02: How does fscanf("%n") behave on end-of-file?

This issue has been automatically converted from the original issue lists and some formatting may not have been preserved.

Authors: Max K. Goff, WG14
Date: 1992-12-10
Reference document: X3J11/90-049
Submitted against: C90
Status: Fixed
Fixed in: C90 TC1
Cross-references: 0167
Converted from: dr.htm, dr_014.html

X/Open Reference Number KRT3.159.2

Subclause 7.9.6.2 The fscanf function states:

If end-of-file is encountered during input, conversion is terminated. If end-of-file occurs before any characters matching the current input directive have been read (other than leading white space, where permitted), execution of the current directive terminates with input failure; otherwise, unless execution of the current directive is terminated with a matching failure, execution of the following directive (if any) is terminated with an input failure.

How should an implementation behave when end-of-file terminates an input stream that satisfies all conversion specifications that consume input but there is a remaining specification request that consumes no input (e.g. %n)? Should the non-input-consuming directive be evaluated or terminated with an input failure as described above?

Comment from WG14 on 1997-09-23:

Correction

Add to subclause 7.9.6.2, page 137, line 4 (the n conversion specifier):

No argument is converted, but one is consumed. If the conversion specification with this conversion specifier is not one of %n, %ln, or %hn, the behavior is undefined.

Add to subclause 7.9.6.2, page 138, another Example:

In:

#include <stdio.h>
 /* ... */
 int d1, d2, n1, n2, i;
 i = sscanf("123", "%d%n%n%d",&d1, &n1, &n2, &d2);

the value 123 is assigned to d1 and the value 3 to n1 . Because %n can never get an input failure the value of 3 is also assigned to n2. The value of d2 is not affected. The value 3 is assigned to i.