[Bug c++/33515] New: Inconsistent warning about "defined but not used"

[Bug c++/33515] New: Inconsistent warning about "defined but not used"

[mec at google dot com]

Consider this code:

  class Alpha { public: Alpha(); };
  static Alpha* a1 = new Alpha;

Should this draw a warning about a1 defined-but-not-used?  gcc 4.3-20070914
gives a warning on some programs but not others.  Specifically, I see the
warning if a program has an unrelated syntax error.  This is odd.

 mec@hollerith:~/exp-defined$ cat z2.cc
class Alpha {
  public:
    Alpha();
    ~Alpha();
  private:
    int i;
};

static Alpha* a1 = new Alpha;

int Beta() {
  return 0;
}

mec@hollerith:~/exp-defined$ /home/mec/gcc-4.3-20070914/install/bin/g++ -Wall
-S z2.cc
mec@hollerith:~/exp-defined$ cat z3.cc
class Alpha {
  public:
    Alpha();
    ~Alpha();
  private:
    int i;
};

static Alpha* a1 = new Alpha;

int Beta() {
  return x;
}

mec@hollerith:~/exp-defined$ /home/mec/gcc-4.3-20070914/install/bin/g++ -Wall
-S z3.cc
z3.cc: In function 'int Beta()':
z3.cc:12: error: 'x' was not declared in this scope
z3.cc: At global scope:
z3.cc:9: warning: 'a1' defined but not used

mec@hollerith:~/exp-defined$


-- 
           Summary: Inconsistent warning about "defined but not used"
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mec at google dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33515

[Bug c++/33515] Inconsistent warning about "defined but not used"

[mec at google dot com]

------- Comment #1 from mec at google dot com  2007-09-21 05:58 -------
Created an attachment (id=14236)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14236&action=view)
Test program

compile with: gcc -Wall -S z2.cc

This program does not give a warning about a1 defined-but-not-used.  I believe
this is correct behavior.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33515

[Bug c++/33515] Inconsistent warning about "defined but not used"

[mec at google dot com]

------- Comment #2 from mec at google dot com  2007-09-21 05:59 -------
Created an attachment (id=14237)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14237&action=view)
Test program

Compile with: gcc -Wall -S z3.cc

This program does give a warning about a1 defined-but-not-used.  I believe this
is incorrect.  The real point is that z2.cc and z3.cc should behave
consistently.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33515

[Bug c++/33515] Inconsistent warning about "defined but not used" when there is an error

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2007-09-21 09:08 -------
I think there is already a bug about this.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Inconsistent warning about  |Inconsistent warning about
                   |"defined but not used"      |"defined but not used" when
                   |                            |there is an error


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33515

[Bug c++/33515] Inconsistent warning about "defined but not used" when there is an error

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2007-09-21 09:09 -------
Yep, PR 32205.

*** This bug has been marked as a duplicate of 32205 ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33515

[Bug c++/33515] Inconsistent warning about "defined but not used" when there is an error

[bangerth at dealii dot org]

------- Comment #5 from bangerth at dealii dot org  2007-09-22 03:57 -------
This code:
----------------
 class Alpha { public: Alpha(); };
  static Alpha* a1 = new Alpha;
----------------
should definitely not draw a warning because during the initialization
of the variable, the constructor of Alpha is run which could have side
effects. Doing stuff like this is actually a fairly frequently used
idiom whereby we can assure that certain resources are already allocated
before we even get to main(). 

W.


-- 

bangerth at dealii dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bangerth at dealii dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33515