I know what you mean. Yet, I wouldn't call it a definition, because it doesn't... quite qualify for that in my opinion. Perhaps they could have worded it different?
The first is after all called a forward declaration. Perhaps a forward declaration could be made distinct from declaration.
Oh well.
Originally Posted by Adak
I have it working now I put the extern line in the header and the second line in only one source file. Thanks
These structs come from a library. When the compiler was suggesting I was defining them, I just though I was creating an instance of them (or actually only a pointer to them). I guess that must amount to having a new struct, thus it has been defined?
P.S.
My 'good' reason is I'm attempting to organise things in a C++ way so I learn it 'right', only I'm obviously not yet.
Last edited by alanb; 08-27-2009 at 05:55 PM.
Describing the layout of your struct is called defining the struct.
Creating an instance of the struct would be ... well, defining a variable of the type of your struct.
Also, say, you say organize in a C++ way, but you are posting in C?
That's what I thought?
I figured since this question was not C++ specific.....I'll get the hang of it.Also, say, you say organize in a C++ way, but you are posting in C?
Multiple source files isn't specific to C either, so...
Plus C++ allows something else that's specific to this topic that C doesn't, namely constants.
Constants in C are usually #defines, but in C++, they can be different.
There is something called a constant expression. A constant expression is basically something that the compiler can understand at compile time, such as a constant (integer, such as 10 or even 20 / 2, etc).
If we add const to a variable and initialize it with a constant expression, then the variable itself becomes a constant expression. That means it isn't treated as a variable, which in turn means that we can put it in a header, like so:
const int n = 50;
And it will work.
Doesn't work in C.
Last edited by Elysia; 08-28-2009 at 11:15 AM.
