libstdc++/10361: ifstream get function failure

[Giovanni Bajo]

The following reply was made to PR libstdc++/10361; it has been noted by GNATS.

From: "Giovanni Bajo" <giovannibajo@libero.it>
To: <gcc-gnats@gcc.gnu.org>,
	<duhovka@tau.ac.il>,
	<gcc-bugs@gcc.gnu.org>,
	<nobody@gcc.gnu.org>,
	<gcc-prs@gcc.gnu.org>,
	<paolo@gcc.gnu.org>
Cc:  
Subject: Re: libstdc++/10361: ifstream get function failure
Date: Wed, 9 Apr 2003 19:57:04 +0200

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&p
 r=10361
 
 Dina Duhovny:
 
 >It IS a BUG. If function 'get(char&)' does not read EOL if it appeares
 > solely in a line, then either you should change the documentation to say
 > so (and call it a "feature") or call it by its name and fix it.
 
 That's _your_ opinion. Official C++ standard says, at §27.6.1.3:
 
 basic_istream<charT,traits>& get(basic_streambuf<char_type,traits>& sb,
 char_type delim );
 
 "Extracts characters and inserts them in the output sequence controlled by
 sb. Characters are
 extracted and inserted until any of the following occurs:
 [...]
 -- c == delim for the next available input character c (in which case c is
 not extracted);
 [...]
 If the function inserts no characters, it calls setstate(failbit), [...]".
 
 Since a blank line only has a "\n", the function will extract no characters,
 and thus will set failbit. You don't clear the failbit, so the function
 fails next time immediatly; you keep waiting for eof, which will never occur
 since no more characters will be read.
 To avoid the infinite loop, you should check simply for !pdb instead of
 !pdb.eof().
 
 Besides, there is a better way to do what you're trying to do: just use
 ifstream::getline(). First, getline() silently skips "\n", so you don't have
 to explicitally call get() to ignore the "\n". Second, it sets the failbit
 if no characters are _EXTRACTED_  from the stream, instead of _STORED_ like
 get(). So, in case of a blank line, the "\n" is extracted and silently
 skipped, the function returns and failbit is not set, so everything
 continues as usual.
 
 
 > Remember, it worked (as it should) before 3.0.
 
 It means that your code was relying on a bug present in libstdc++ before 3.0
 It does not mean that your code should work.
 
 Giovanni Bajo