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

[gccbugs@contacts.eelis.net]

>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: