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digitalmars.D - "Need 'this' to access structure member"

reply alxdef <alxdef_member pathlink.com> writes:
Hi there!
I am beginner in D and I confused with subject.
Here my source:

Module some_mod.d ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
module some_mod;
struct struct1
{
union addr
{
struct
{
ushort offs;
ushort seg;
}
uint flat;
};
};
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In main.d ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
import some_mod;
struct1 s;
s.addr.flat = 0;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Compile command: DMD main.d some_mod.d

At this point compiler says the subject message. When I make 'offs', 'seg', and
'flat' as static compilation is well, but it is not what I need, cause fields of
union is unmodifiable. Could someone help with this?
Thanks a lot!

Sorry for my English!
Jun 22 2006
parent Derek Parnell <derek nomail.afraid.org> writes:
On Fri, 23 Jun 2006 05:59:50 +0000 (UTC), alxdef wrote:

 Hi there!
 I am beginner in D and I confused with subject.
 Here my source:
 
 Module some_mod.d ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 module some_mod;
 struct struct1
 {
 union addr
 {
 struct
 {
 ushort offs;
 ushort seg;
 }
 uint flat;
 };
 };
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 In main.d ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 import some_mod;
 struct1 s;
 s.addr.flat = 0;
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Compile command: DMD main.d some_mod.d
 
 At this point compiler says the subject message. When I make 'offs', 'seg', and
 'flat' as static compilation is well, but it is not what I need, cause fields
of
 union is unmodifiable. Could someone help with this?
 Thanks a lot!

You have two choices. (1) Choice #1. Module some_mod.d ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ module some_mod; struct struct1 { union addr { struct { ushort offs; ushort seg; } uint flat; }; addr a; }; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In main.d ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ import some_mod; struct1 s; s.a.flat = 0; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ (2) Choice #2. Module some_mod.d ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ module some_mod; struct struct1 { union { struct { ushort offs; ushort seg; } uint flat; }; }; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In main.d ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ import some_mod; struct1 s; s.flat = 0; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Now to explain... The first choice uses a named Union. You called it 'addr'. But in D, can't define a named union (or struct) and declare an instance of it in the same statement. You have to use two statements ... for example: // Define the named union. union somename { int a; long b; } // Declare an instance of it. somename foo; Once you have an instance of it, you can use it to access the union members ... foo.a = 1; The second choice uses an unnamed (anonymous) union. In this case, when you define a anonymous union you cannot declare an instance of separately (because it doesn't have a name) so the definition also serves as the declaration. You then access its members directly, again because there is no instance name you can't use it. // Define the anonymous union. union { int a; long b; } Once you have an instance of it, you can use it to access the union members ... a = 1; *But* you can only define anonymous unions and structs if there are inside a union or struct. So the top-level container must have a name. Anyhow, here your example reworked ... ---------some_mod.d ------------- module some_mod; struct struct1 { union { struct { ushort offs; ushort segm; } uint flat; } } --------------------------------- ----------- main.d --------------- import some_mod; import std.stdio; void main() { struct1 s; s.flat = 0xFFEEDDCC; writefln("%x %x", s.offs, s.segm); } --------------------------------- This displays "ddcc ffee" when run. -- Derek (skype: derek.j.parnell) Melbourne, Australia "Down with mediocrity!" 23/06/2006 4:21:25 PM
Jun 22 2006