[STDCXX-1059] std::ios_base::setf() and std::ios_base::unsetf() do not set/clear the format flags correctly

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 4.2.1, 4.2.x, 4.3.x, 5.0.0
• Fix Version/s: 4.2.2, 4.2.x, 4.3.x, 5.0.0
• Component/s: 27. Input/Output
• Labels: conformance runtime standards

Environment

Solaris 10 and 11
Red Hat Linux, OpenSuSE Linux
Sun C++ Compilers 12.1, 12.2, 12.3

Defect is independent of platform and/or compiler

• Regression: Regression, Unit Test Broken
• Severity: Incorrect Behavior
• Assignee: Unassigned
• Reporter: Stefan Teleman
• Created: 05/Feb/12 20:34
• Updated: 25/Sep/12 23:58
• Resolved: 25/Sep/12 23:58

Description

std::ios_base::setf (fmtflags fl) and std::ios_base::unsetf (fmtflags fl)
do not set or clear the format flags correctly:

test.cc

#include <ios>
#include <iostream>
#include <fstream>

int main()
{
    std::fstream strm;
    std::ios_base::fmtflags fl;
    int ret = 0;

    fl = std::ios_base::dec;
    strm.unsetf(fl);

    fl = std::ios_base::hex;

    strm.setf(fl);
    strm.unsetf(fl);

    if (strm.flags() & fl)
    {
        std::cerr << "failure to clear hex flags" << std::endl;
        ++ret;
    }

    return ret;
}

1. Output from GCC 4.5.0:

[steleman@darthvader][/src/steleman/programming/stdcxx-ss122/bugfixes-sunw/fmtflags][02/05/2012 15:19:37][1957]>> ./test-gcc 
[steleman@darthvader][/src/steleman/programming/stdcxx-ss122/bugfixes-sunw/fmtflags][02/05/2012 15:20:02][1958]>> echo $status
0

2. Output from Sun C++ 12.2 with stlport:

[steleman@darthvader][/src/steleman/programming/stdcxx-ss122/bugfixes-sunw/fmtflags][02/05/2012 15:20:24][1959]>> ./test-ss122-stlport 
[steleman@darthvader][/src/steleman/programming/stdcxx-ss122/bugfixes-sunw/fmtflags][02/05/2012 15:21:08][1960]>> echo $status
0

3. Output rom Sun C++ 12.2 with our patched stdcxx:

[steleman@darthvader][/src/steleman/programming/stdcxx-ss122/bugfixes-sunw/fmtflags][02/05/2012 15:21:09][1961]>> ./test-ss122-stdcxx 
[steleman@darthvader][/src/steleman/programming/stdcxx-ss122/bugfixes-sunw/fmtflags][02/05/2012 15:21:44][1962]>> echo $status
0

4. Output from Pathscale 4.0.12.1 (which did not patch stdcxx):

[steleman@darthvader][/src/steleman/programming/stdcxx-ss122/bugfixes-sunw/fmtflags][02/05/2012 15:21:46][1963]>> ./test-pathscale 
failure to clear hex flags
[steleman@darthvader][/src/steleman/programming/stdcxx-ss122/bugfixes-sunw/fmtflags][02/05/2012 15:22:48][1964]>> echo $status
1

Simplified test case identifying the problem:

flags.cc

#include <iostream>
#include <ios>

class BadTest
{
public:
    BadTest() : _flags(0) { }
    ~BadTest() { }

    unsigned int flags() const { return _flags; }
    unsigned int flags (unsigned int f)
    {
        unsigned int ret = _flags;
        _flags |= f;
        return ret;
    }
    unsigned int setf (unsigned int f) { return flags (flags() | f); }
    void unsetf (unsigned int f) { flags (flags() & ~f); }

private:
    unsigned int _flags;
};

class GoodTest
{
public:
    GoodTest() : _flags(0) { }
    ~GoodTest() { }

    unsigned int flags() const { return _flags; }
    unsigned int flags (unsigned int f)
    {
        unsigned int ret = _flags;
        _flags |= f;
        return ret;
    }
    unsigned int setf (unsigned int f)
    {
        unsigned int ret = _flags;
        _flags |= f;
        return ret;
    }
    void unsetf (unsigned int f) { _flags &= ~f; }

private:
    unsigned int _flags;
};

int main()
{
    BadTest bt;
    std::ios_base::fmtflags fl;

    std::cerr << "***** BadTest *****" << std::endl;
    std::cerr << "default flags: " << bt.flags() << std::endl;

    fl = std::ios_base::dec;

    bt.setf(fl);
    std::cerr << "flags: " << bt.flags() << std::endl;

    bt.unsetf(fl);
    std::cerr << "flags: " << bt.flags() << std::endl;

    fl = std::ios_base::hex;

    bt.setf(fl);
    std::cerr << "flags: " << bt.flags() << std::endl;

    bt.unsetf(fl);
    std::cerr << "flags: " << bt.flags() << std::endl;

    std::cerr << std::endl;

    GoodTest gt;
    std::cerr << "***** GoodTest *****" << std::endl;
    std::cerr << "default flags: " << gt.flags() << std::endl;

    fl = std::ios_base::dec;

    gt.setf(fl);
    std::cerr << "flags: " << gt.flags() << std::endl;

    gt.unsetf(fl);
    std::cerr << "flags: " << gt.flags() << std::endl;

    fl = std::ios_base::hex;

    gt.setf(fl);
    std::cerr << "flags: " << gt.flags() << std::endl;

    gt.unsetf(fl);
    std::cerr << "flags: " << gt.flags() << std::endl;

    return 0;
}

1. Output from GCC 4.5.0:

[steleman@darthvader][/src/steleman/programming/stdcxx-ss122/bugfixes-sunw/fmtflags][02/05/2012 15:27:01][1968]>> ./flags-gcc 
***** BadTest *****
default flags: 0
flags: 2
flags: 2
flags: 10
flags: 10

***** GoodTest *****
default flags: 0
flags: 2
flags: 0
flags: 8
flags: 0

2. Output from Sun C++ 12.2 with stlport:

[steleman@darthvader][/src/steleman/programming/stdcxx-ss122/bugfixes-sunw/fmtflags][02/05/2012 15:27:05][1969]>> ./flags-ss122-stlport 
***** BadTest *****
default flags: 0
flags: 8
flags: 8
flags: 24
flags: 24

***** GoodTest *****
default flags: 0
flags: 8
flags: 0
flags: 16
flags: 0

3. Output from Sun C++ 12.2. with our patched stdcxx:

[steleman@darthvader][/src/steleman/programming/stdcxx-ss122/bugfixes-sunw/fmtflags][02/05/2012 15:27:12][1970]>> ./flags-ss122-stdcxx 
***** BadTest *****
default flags: 0
flags: 2
flags: 2
flags: 10
flags: 10

***** GoodTest *****
default flags: 0
flags: 2
flags: 0
flags: 8
flags: 0

The defect is in

std::ios_base::setf(fmtflags fl);
and
std::ios_base::unsetf(fmtflags fl);

in the original stdcxx implementation. The member function

fmtflags std::ios_base::flags() const;

returns by value. Any bitwise operations on the anon temporary created by
this function do not affect the __fmtflags data member of std::ios_base,
which remains unchanged.

Patch for stdcxx 4.2.1 to follow.