const static linking problem

[Shuo Xiang]

Greetings:

For the following code:

class foo
{
...
private:
static const int x=3;
}

void foo::bar()
{
int i=x;
}

---

When it is linked the linker always complains of "undefined reference to
`foo::x'", why?

Regards,

Shuo

[Andrey Tarasevich]

Re: const static linking problem

Shuo Xiang wrote:[color=blue]
> ...
> For the following code:
>
> class foo
> {
> ...
> private:
> static const int x=3;
> }
>
> void foo::bar()
> {
> int i=x;
> }
>
> ---
>
> When it is linked the linker always complains of "undefined reference to
> `foo::x'", why?
> ...[/color]

Because you forgot to define object 'foo::x' in your program. The
declaration is present, but the definition is missing. Provide a
definition and everything should compile without a problem

class foo
{
...
private:
static const int x = 3;
};

const int foo::x;

void foo::bar()
{
int i = x;
}

Note, that the new (post TC1) version of C++ standard no longer requires
'foo::x' to be defined for this particular code to compile. But your
compiler seems to follow the requirements of the original C++ standard.

--
Best regards,
Andrey Tarasevich
Brainbench C and C++ Programming MVP

[Shuo Xiang]

Re: const static linking problem

Andrey Tarasevich wrote:
[color=blue]
> Shuo Xiang wrote:[color=green]
>> ...
>> For the following code:
>>
>> class foo
>> {
>> ...
>> private:
>> static const int x=3;
>> }
>>
>> void foo::bar()
>> {
>> int i=x;
>> }
>>
>> ---
>>
>> When it is linked the linker always complains of "undefined reference to
>> `foo::x'", why?
>> ...[/color]
>
> Because you forgot to define object 'foo::x' in your program. The
> declaration is present, but the definition is missing. Provide a
> definition and everything should compile without a problem
>
> class foo
> {
> ...
> private:
> static const int x = 3;
> };
>
> const int foo::x;
>
> void foo::bar()
> {
> int i = x;
> }
>
> Note, that the new (post TC1) version of C++ standard no longer requires
> 'foo::x' to be defined for this particular code to compile. But your
> compiler seems to follow the requirements of the original C++ standard.
>[/color]

Greetings:

Thank you! It was very helpful.

Regards,

Shuo