[Bug c++/18016] New: -Winit-self misses member variables initialized after : in ctor

[Bug c++/18016] New: -Winit-self misses member variables initialized after : in ctor

[ejb at ql dot org]

First, my gcc version information:

% gcc -v
Reading specs from /usr/lib/gcc/i486-linux/3.4.2/specs
Configured with: ../src/configure -v
--enable-languages=c,c++,java,f77,pascal,objc,ada,treelang --prefix=/usr
--libexecdir=/usr/lib --with-gxx-include-dir=/usr/include/c++/3.4
--enable-shared --with-system-zlib --enable-nls --without-included-gettext
--program-suffix=-3.4 --enable-__cxa_atexit --enable-libstdcxx-allocator=mt
--enable-clocale=gnu --enable-libstdcxx-debug --enable-java-gc=boehm
--enable-java-awt=gtk --disable-werror i486-linux
Thread model: posix
gcc version 3.4.2 (Debian 3.4.2-2)

This is the gcc-3.4 package in debian, FYI, but this bug is not likely to be
debian-specific.

I'm excited to see the -Winit-self warning, but it fails to catch a common
problem, as illustrated by this code fragment (which I will include inline and
also as an attachment for convenience).  This code has two cases of variables
initialized with themselves: one trivial int b = b case, and one more subtle A()
: a(a) case.  g++ warns for one but not the other.  Use this command:

g++-3.4 -c -Winit-self -Wuninitialized -O1 a.cc

on this file:
class A
{
  public:
    A() : a(a)  // <-- should generate a warning
    {
    }
    int getA()
    {
	int b = b;  // <-- generates warning as it should
	return this->a + b;
    }

  private:
    int a;
};

int main()
{
    A a;
    return a.getA();
}


generates this output:

a.cc: In function `int main()':
a.cc:9: warning: 'b' might be used uninitialized in this function

It fails to warn for A::a being initialized with itself in the constructor.

One might also consider it to be a problem that A::getA's being inlined causes
the warning message to mention main() rather than getA() -- this problem is not
present if getA is not inlined.  Anyway, the line number is okay, so this seems
pretty unimportant though still worthy of mention.

It would also be nice if -Winit-self would automatically add -Wuninitialized
instead of just not doing anything unless -Wuninitialized was also specified. 
I'll mention that in a separate bug report.

-- 
           Summary: -Winit-self misses member variables initialized after :
                    in ctor
           Product: gcc
           Version: 3.4.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ejb at ql dot org
                CC: ejb at ql dot org,gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i486-linux
  GCC host triplet: i486-linux
GCC target triplet: i486-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18016

[Bug c++/18016] -Winit-self misses member variables initialized after : in ctor

[ejb at ql dot org]

------- Additional Comments From ejb at ql dot org  2004-10-15 16:46 -------
Created an attachment (id=7358)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=7358&action=view)
source file that reproduces problem

This attachment contains the code that is also inlined in the bug report.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18016

[Bug c++/18016] Warn about member variables initialized with itself

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-10-15 17:05 -------
-Winit-self has nothing to do with this problem really.

in this case :a(a) is equivalent to this->a = this->a;

We should warn about this case even without -Winit-self or even -Wuninitialize as we can warn without
optimization turned on.

Note I added -Winit-self so I know what it was designed to do.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
           Keywords|                            |diagnostic
   Last reconfirmed|0000-00-00 00:00:00         |2004-10-15 17:05:57
               date|                            |
            Summary|-Winit-self misses member   |Warn about member variables
                   |variables initialized after |initialized with itself
                   |: in ctor                   |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18016

[Bug c++/18016] Warn about member variables initialized with itself

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2004-10-28 03:35 -------
> -Winit-self has nothing to do with this problem really.
> in this case :a(a) is equivalent to this->a = this->a;

Not really. The member-list syntax is used to *initialize* the members, not to 
assign a value to them after a default initialization.

I think it makes sense to warn only with -Winit-self.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18016

[Bug c++/18016] Warn about member variables initialized with itself

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-10-28 13:08 -------
That is my view, too. It's an initializer, not an assignment. 
W. 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18016