libstdc++/7989: ios::showbase doesn't work when outputting 0

libstdc++/7989: ios::showbase doesn't work when outputting 0

[lennox]

>Number:         7989
>Category:       libstdc++
>Synopsis:       ios::showbase doesn't work when outputting 0
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Sep 20 09:16:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     lennox@cs.columbia.edu
>Release:        gcc-3.1
>Organization:
>Environment:

>Description:
When I run the attached program, I expect to see the output
0x0005
0x0000

Instead, with gcc 3.1, I get
0x0005
000000

gcc 2.95.2 is correct, so this is a regression.
>How-To-Repeat:
Compile and run the attached program.
>Fix:
None known.

As a workaround, don't use ios::showbase, and instead output the 0x explicitly.
>Release-Note:
>Audit-Trail:
>Unformatted:
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Re: libstdc++/7989: ios::showbase doesn't work when outputting 0

[Jonathan Lennox]

The following reply was made to PR libstdc++/7989; it has been noted by GNATS.

From: Jonathan Lennox <lennox@cs.columbia.edu>
To: paolo@gcc.gnu.org, gcc-bugs@gcc.gnu.org, gcc-prs@gcc.gnu.org,
   nobody@gcc.gnu.org, gcc-gnats@gcc.gnu.org
Cc:  
Subject: Re: libstdc++/7989: ios::showbase doesn't work when outputting 0
Date: Fri, 27 Sep 2002 10:34:33 -0400

 On , September 26 2002, "paolo@gcc.gnu.org" wrote to "gcc-bugs@gcc.gnu.org, gcc-prs@gcc.gnu.org, lennox@cs.columbia.edu, nobody@gcc.gnu.org, paolo@gcc.gnu.org" saying:
 
 >     Only with gcc-3.1 the output is the same for both, that is:
 >     0x5
 >     0
 >     In fact, the ISO/IEC Standard 14882 for C++ prescribes (22.2.2.2.2 and table 57) that the output must be identical to that obtained with the "%#x" format for the C library
 >     function printf().
 >     Thanks for your report, Paolo.
 
 Ah yes, and 9899-1999 says "for x (or X) a non-zero result has 0x (or 0X)
 prefixed to it."  How odd, but I agree this behavior is correct.
 
 Thanks.
 
 -- 
 Jonathan Lennox
 lennox@cs.columbia.edu

Re: libstdc++/7989: ios::showbase doesn't work when outputting 0

[paolo]

Synopsis: ios::showbase doesn't work when outputting 0

Responsible-Changed-From-To: unassigned->paolo
Responsible-Changed-By: paolo
Responsible-Changed-When: Thu Sep 26 12:44:00 2002
Responsible-Changed-Why:
    Analyzed.
State-Changed-From-To: open->closed
State-Changed-By: paolo
State-Changed-When: Thu Sep 26 12:44:00 2002
State-Changed-Why:
    Not a bug: gcc-2.95.2 is *incorrect*.
    Indeed, for simplicity sake, compare
    <C>:
    #include <stdio.h>
    int main()
    {
      printf("%#x\n", 5);
      printf("%#x\n", 0);
      return 0;
    }
    vs <C++>:
    #include <iostream>
    using namespace std;
    int main()
    {
      cout.setf(ios::showbase);
      cout.setf(ios::hex, ios::basefield);
      cout << 5 << endl;
      cout << 0 << endl;
    }
    Only with gcc-3.1 the output is the same for both, that is:
    0x5
    0
    In fact, the ISO/IEC Standard 14882 for C++ prescribes (22.2.2.2.2 and table 57) that the output must be identical to that obtained with the "%#x" format for the C library
    function printf().
    Thanks for your report, Paolo.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7989