static inline member function

[Martin Vorbrodt]

so if i have this:

// header.h
class X {
public:
static int s = 1;
};

i still need this:

// source.cpp
int X::s;

right?

what about this:

class X {
public:
static int S() { return 1; }
};

how come static member needs definition outside the class, but static member
can be inlined? i don't quite understand how that is allowed. and why.

please explain

[Mike Wahler]

"Martin Vorbrodt" <mv*******@gmail.com> wrote in message
news:Jo*****************@news-wrt-01.rdc-nyc.rr.com...

so if i have this:

// header.h
class X {
public:
static int s = 1;
};

i still need this:

// source.cpp
int X::s;

right?
Yes.

what about this:

class X {
public:
static int S() { return 1; }
};

how come static member needs definition outside the class, but static
member can be inlined?
Static data members occur only once, not per
object instance. When you create an object,
memory for all the non-static data members is
alloted, for each object. IOW the memory is
'inside' the objects. The static member occurs
only once. So you need to provide it somewhere.

Also, note that the concept of 'inline' really
only has meaning for functions, not data.

No matter how many objects you create, there is
still only one copy of each member function, whether
'inlined' or not. 'inline' (specified by either
putting a function definition inside a class body,
or outside it with the 'inline' keyword, is a 'hint'
to the compiler to try to insert the function body
at the point of call, rather than have it 'really'
call and return. But note that a compiler is free
to honor or ignore such a 'hint'.

i don't quite understand how that is allowed. and why.

I hope my explanation helped.

-Mike

[Martin Vorbrodt]

"Mike Wahler" <mk******@mkwahler.net> wrote in message
news:6H*****************@newsread2.news.pas.earthl ink.net...

"Martin Vorbrodt" <mv*******@gmail.com> wrote in message
news:Jo*****************@news-wrt-01.rdc-nyc.rr.com...

so if i have this:

// header.h
class X {
public:
static int s = 1;
};

i still need this:

// source.cpp
int X::s;

right?
Yes.

so putting int X::s in header file right after class definition, and later
including that file more than once, could yeld link errors?

what about this:

class X {
public:
static int S() { return 1; }
};

how come static member needs definition outside the class, but static
member can be inlined?
Static data members occur only once, not per
object instance. When you create an object,
memory for all the non-static data members is
alloted, for each object. IOW the memory is
'inside' the objects. The static member occurs
only once. So you need to provide it somewhere.

so why isn't "static int s = 1;" declared (and defined?) inside the class
enough? why must i put it in CPP file?

Also, note that the concept of 'inline' really
only has meaning for functions, not data.

No matter how many objects you create, there is
still only one copy of each member function, whether
'inlined' or not. 'inline' (specified by either
putting a function definition inside a class body,
or outside it with the 'inline' keyword, is a 'hint'
to the compiler to try to insert the function body
at the point of call, rather than have it 'really'
call and return. But note that a compiler is free
to honor or ignore such a 'hint'.

i don't quite understand how that is allowed. and why.

I hope my explanation helped.

-Mike

[Mike Wahler]

"Martin Vorbrodt" <mv*******@gmail.com> wrote in message
news:ew****************@news-wrt-01.rdc-nyc.rr.com...

"Mike Wahler" <mk******@mkwahler.net> wrote in message
news:6H*****************@newsread2.news.pas.earthl ink.net...

"Martin Vorbrodt" <mv*******@gmail.com> wrote in message
news:Jo*****************@news-wrt-01.rdc-nyc.rr.com...

so if i have this:

// header.h
class X {
public:
static int s = 1;
};

i still need this:

// source.cpp
int X::s;

right?
Yes.

so putting int X::s in header file right after class definition, and later
including that file more than once, could yeld link errors?

Yes, it would violate the 'one definition rule' (ODR)

what about this:

class X {
public:
static int S() { return 1; }
};

how come static member needs definition outside the class, but static
member can be inlined?
Static data members occur only once, not per
object instance. When you create an object,
memory for all the non-static data members is
alloted, for each object. IOW the memory is
'inside' the objects. The static member occurs
only once. So you need to provide it somewhere.

so why isn't "static int s = 1;" declared (and defined?)

It's not defined, only declared.

inside the class enough?
Because it's only a declaration, not a definition.
The initializer is allowed as a 'special case'
for static constant integer types (which means
-- I didn't notice it before -- that what you
had is not valid, since it's not const).
why must i put it in CPP file?

Because it still needs to be defined (storage
allotted for it).

-Mike

[Jay Nabonne]

On Fri, 21 Oct 2005 00:21:30 +0000, Martin Vorbrodt wrote:

so why isn't "static int s = 1;" declared (and defined?) inside the class
enough? why must i put it in CPP file?

You can't do what that line above says. You can only initialize static
*const* integral types.

If it was that case that you did have "static const", then you may *not*
have to put it in the cpp file, assuming you don't take its address or do
anything else funky with it, and assuming the compiler uses the const
value directly.

- Jay

[Martin Vorbrodt]

"Jay Nabonne" <ja*********@sonicNOSPAM.com> wrote in message
news:pa****************************@sonicNOSPAM.co m...

On Fri, 21 Oct 2005 00:21:30 +0000, Martin Vorbrodt wrote:

so why isn't "static int s = 1;" declared (and defined?) inside the class
enough? why must i put it in CPP file?
You can't do what that line above says. You can only initialize static
*const* integral types.

If it was that case that you did have "static const", then you may *not*
have to put it in the cpp file, assuming you don't take its address or do
anything else funky with it, and assuming the compiler uses the const
value directly.

According to the standard:

If a static data member is of const integral or const enumeration type, its
declaration in the class definition can specify a constant initializer which
shall be an integral constant expression (5.19). In that case, the member
can appear in integral constant expressions within its scope. The member
shall still be defined in a namespace scope if it is used in the program and
the namespace scope definition shall not contain an initializer.

sooo... you can give it a value in the calss definition and use it in
constant int* expressions (expressions evaluated at compile time, right?),
but apparently you still need to put it in some CPP file to allocate space
for it? am i reading this right (english is my 2nd language, and standard
ain't plain vanilla english:) )

so what do you mean by not doing funky things to it? not using it in any
other way than in const integral expressions?

- Jay