Re: c++/10416: 'unused variable' warning ignores ctor/dtor side-effects

Re: c++/10416: 'unused variable' warning ignores ctor/dtor side-effects

[bangerth]

Synopsis: 'unused variable' warning ignores ctor/dtor side-effects

State-Changed-From-To: open->closed
State-Changed-By: bangerth
State-Changed-When: Wed Apr 16 23:15:53 2003
State-Changed-Why:
    The compiler cannot know what you want. If you don't like
    the warning, switch it off, or follow what the manual
    says:
    
    @item -Wunused-variable
    @opindex Wunused-variable
    Warn whenever a local variable or non-constant static variable is unused
    aside from its declaration
    
    To suppress this warning use the @samp{unused} attribute
    (@pxref{Variable Attributes}).
    
    W.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10416

c++/10416: 'unused variable' warning ignores ctor/dtor side-effects

[gccbugs]

>Number:         10416
>Category:       c++
>Synopsis:       'unused variable' warning ignores ctor/dtor side-effects
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    unassigned
>State:          open
>Class:          pessimizes-code
>Submitter-Id:   net
>Arrival-Date:   Tue Apr 15 18:56:00 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     Eelis van der Weegen
>Release:        gcc 3.2
>Organization:
>Environment:

>Description:
Sometimes a variable is created only for the side-effects of its constructor/destructor. For example, in the following code:

struct Closer { ~Closer() { CloseClipboard(); } } closer;

the closer variable is only used to make sure the clipboard is closed when the function leaves (normally or exceptionally).

G++ apparently does not think this is valid use of a variable, and warns: "warning: unused variable".
>How-To-Repeat:
Compile:

void f () { struct atend { ~atend () { std::cout << "leaving f\n"; } } a; }

with -Wall.
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: