Something with static...

Why is this struct illegal:

#include<iostream>

struct debug {
std::string d1 = "bob\n";
};

I get this error:

graphics/debug.h:4: error: ISO C++ forbids initialization of member ‘d1’
graphics/debug.h:4: error: making ‘d1’ static
graphics/debug.h:4: error: invalid in-class initialization of static
data member of non-integral type ‘std::string’

If I change it to:

static std::string d1 = "bob\n";

I only get:

graphics/debug.h:4: error: invalid in-class initialization of static
data member of non-integral type ‘std::string’

I have also tried:

struct debug {
std::string d1 = getd1();
std::string getd1(){
return "bob\n";
}
};

But then I get:

graphics/debug.h:4: error: a function call cannot appear in a
constant-expression


I thought it was ok to call a function in a struct.

re: Something with static...

desktop wrote:Because the language says it is.

You can only define static const integral types in class declarations.
You have to declare the static member in the class declaration and
define it in a single compilation unit.

--
Ian Collins.

re: Something with static...

"desktop" <fff@sss.comwrote in message
news:fdac8b$c5o$1@news.net.uni-c.dk...Try this.

struct debug {
std::string d1;
debug(): d1( "bob\n" ){}
}

That's called an "initializaiton list". But it is no longer a POD (plain
old data).

[SNIP]

re: Something with static...

On Tue, 25 Sep 2007 09:10:35 +0200, desktop wrote:In-class initialization of data members is only allowed for
static const POD types.

For example:
struct debug
{
static const int = 5;
};

To initialize your code, you need to use a constructor:

struct debug
{
std::string d1;

debug() : d1("bob\n") { }
};

That's where a function call also is okay:

struct debug
{
std::string d1;

debug() : d1(getd1()) { }

const std::string getd1() const { return "bob\n"; }
};

--
Joel Yliluoma - http://bisqwit.iki.fi/
: comprehension = 1 / (2 ^ precision)

re: Something with static...

Joel Yliluoma wrote:No, only integral types. You can't write

static const float f = 42.0;

for example.

--
Ian Collins.

re: Something with static...

On Sep 25, 9:10 am, desktop <f...@sss.comwrote:And what is it supposed to mean? There's a d1 for every
instance of the class; if you want to initialize it, you do so
in the constructor.
The declaration of a static member in a class is just that; a
declaration, and not a definition. (There are technical
reasons, largely historic, for this, and I don't see it changing
any time soon.) Since it's only a declaration: 1) you need to
provide a definition somewhere, and 2) you can't initialize it.
(The initialization belongs in the definition.)

There is a special exception to this rule for static members
with a const integral type, and which is initialized with a
constant integral expression; in this case (and only in this
case), the initialization can be provided in the declaration in
the class body (but you still need to provide a definition).
You can *define* a function in a class, and you can call
anything from a that function, but a class defines a data type,
and is not executable code.

--
James Kanze (GABI Software) email:james.kanze@gmail.com
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