Re: const pointer to class problem

t.wanat@[EMAIL PROTECTED]
 wrote:

> class FOO
>   {
> public:
>     int Version(void){return m_ver;};
>     FOO(){m_ver = 1;};
> private:
>     int m_ver;
>   };
>
> void PrintVer(const FOO * fp)
>   {
>   int v = fp->Version();  /* error here */
>
>   cout << "The version is " << v << endl;
>   }
>
> When I try to compile, I get the error
> 'FOO::Version' cannot convert 'this' pointer from 'const FOO' to 'FOO
> &'
>
> on the line containing fp->Version().
>
> If I remove the const from the routine declaration, it works fine, but
> I'd rather not do that.   I guess I don't understand what the compiler
> is trying to tell me, and have no idea of how to work around this
> without removing the const.

When you have a pointer to a const object, you can only call const
member functions via this pointer. Your compiler is trying to tell you
that FOO:Version should be changed to:

    int Version() const { return m_ver; }

(the void is a C-ism and unnecessary). Version() does not change the
state of FOO, hence it should be const.

As an aside, all-caps identifiers should be reserved for preprocessor
macros if you want to avoid name clashes.

-- 
Gerhard Menzl

Non-spammers may respond to my email address, which is composed of my
full name, separated by a dot, followed by at, followed by "fwz",
followed by a dot, followed by "aero".



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