[Development] Best practice for defining an integer constant

[Mandeep Sandhu]

On Fri, Feb 14, 2014 at 10:33 PM, Thiago Macieira <thiago.macieira at intel.com
> wrote:

> Em sex 14 fev 2014, às 15:59:28, Mandeep Sandhu escreveu:
> > I have a need for defining an integer constant that'll be used for
> > initializing a member variable of a private class.
> >
> > The Qt coding conventions (http://qt-project.org/wiki/Coding-Conventions
> )
> > recommend using an enum over 'const int'.
> >
> > The rationale given there is that an enum will be replaced at
> compile-time
> > resulting in 'faster code'. Won't that be the case with 'const int' as
> > well? I think a 'const int' will be inlined in the code. CMIIW.
>
> That is the case, *except* if you pass it via const-ref. If you do that,
> then
> ODR kicks in and you need to have the variable defined somewhere.
>
> For variables in the file scope, the declaration is the definition, so
> it's not
> a problem. For variables in a class scope, the static const declaration is
> *not* the definition.
>
> Try it:
>
> struct Foo
> {
>         static const int Max = 128;
> };
>
> void f()
> {
>         QHash<int, QString> hash;
>         hash.insert(Foo::Max, "Max");
> }
>
> Hint:
>     iterator insert(const Key &key, const T &value);
>
> (const ref for the key)
>

Yes the above would require "const int Foo:Max = 128" somewhere. Even then,
why is that a problem? For single values, I still enum seems like an
overkill.

-mandeep


>
> --
> Thiago Macieira - thiago.macieira (AT) intel.com
>   Software Architect - Intel Open Source Technology Center
>
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