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digitalmars.D - DMD problem: incorrect struct.sizeof

reply Jascha Wetzel <"[firstname]" mainia.de> writes:
Something's weird if you put a ubyte, byte oder char at the end of a
struct. The program below prints
str1.sizeof: 4
str2.sizeof: 8
str3.sizeof: 12
Reproducable with DMD 1.0, 1.001 and 1.002 on win32 - I didn't check
older versions.

import std.stdio;
struct str1 {
	ushort		a;
	ubyte		b;
}
struct str2 {
	uint		a;
	ubyte		b;
}
struct str3 {
	ushort		a;
	uint		c;
	ubyte		b;
}
void main()
{
	writefln("str1.sizeof: %d", str1.sizeof);
	writefln("str2.sizeof: %d", str2.sizeof);
	writefln("str3.sizeof: %d", str3.sizeof);
}
Jan 25 2007
parent reply "Tomas Lindquist Olsen" <tomas famolsen.dk> writes:
Jascha Wetzel wrote:


 Something's weird if you put a ubyte, byte oder char at the end of a
 struct. The program below prints
 str1.sizeof: 4
 str2.sizeof: 8
 str3.sizeof: 12
 Reproducable with DMD 1.0, 1.001 and 1.002 on win32 - I didn't check
 older versions.
 
 import std.stdio;
 struct str1 {
 	ushort		a;
 	ubyte		b;
 }
 struct str2 {
 	uint		a;
 	ubyte		b;
 }
 struct str3 {
 	ushort		a;
 	uint		c;
 	ubyte		b;
 }
 void main()
 {
 	writefln("str1.sizeof: %d", str1.sizeof);
 	writefln("str2.sizeof: %d", str2.sizeof);
 	writefln("str3.sizeof: %d", str3.sizeof);
 }



They are being padded to play nice with 32 bit alignment.

Try:

import std.stdio;
struct str1 {
    align(1):
    ushort      a;
    ubyte       b;
}
struct str2 {
    align(1):
    uint        a;
    ubyte       b;
}
struct str3 {
    align(1):
    ushort      a;
    uint        c;
    ubyte       b;
}
void main()
{
    writefln("str1.sizeof: %d", str1.sizeof);
    writefln("str2.sizeof: %d", str2.sizeof);
    writefln("str3.sizeof: %d", str3.sizeof);
}

--
Jan 25 2007
parent Jascha Wetzel <"[firstname]" mainia.de> writes:
oh, duh, sorry for that...

Tomas Lindquist Olsen wrote:

 They are being padded to play nice with 32 bit alignment.
Jan 25 2007