How the memory layout of global variable is reliable ?
Hello, I have an idea about a small code tool related to the
application resources.
It would rely on the assumption that some global variabled,
sharing the same type and attributes, declared in group, are
contiguous.
In short I need to know if the following assertions are always
true and reliable over time:
--
import std.stdio;
// used as base adress
static string beg = "";
// arbitrary generated by a tool and mixed at compile time.
static string a = "";
static string b = "";
static string c = "";
static string d = "";
static string e = "";
static string f = "";
void main(string args[])
{
void* offs = &beg;
assert( &a == (offs + (size_t.sizeof * 2) * 1) ); // length +
ptr
assert( &b == (offs + (size_t.sizeof * 2) * 2) ); // length +
ptr
assert( &c == (offs + (size_t.sizeof * 2) * 3) ); // etc.
assert( &d == (offs + (size_t.sizeof * 2) * 4) );
}
--
In a second time I need to be sure that the return tuple of the
trait "allMembers" follow the declarations order. The
documentation says that:
"The order in which the strings appear in the result is not
defined".
But so far, it looks like it's ordered according to the
declaration (at least for a module containing only some global
variables).
Any other remarks about the topic are welcome.
Re: How the memory layout of global variable is reliable ?
On Wednesday, 22 October 2014 at 20:37:43 UTC, Freddy wrote:
On Wednesday, 22 October 2014 at 20:29:58 UTC, Cjkp wrote:
Hello, I have an idea about a small code tool related to the
application resources.
It would rely on the assumption that some global variabled,
sharing the same type and attributes, declared in group, are
contiguous.
In short I need to know if the following assertions are always
true and reliable over time:
--
import std.stdio;
// used as base adress
static string beg = "";
// arbitrary generated by a tool and mixed at compile time.
static string a = "";
static string b = "";
static string c = "";
static string d = "";
static string e = "";
static string f = "";
void main(string args[])
{
void* offs = &beg;
assert( &a == (offs + (size_t.sizeof * 2) * 1) ); // length
+ ptr
assert( &b == (offs + (size_t.sizeof * 2) * 2) ); // length
+ ptr
assert( &c == (offs + (size_t.sizeof * 2) * 3) ); // etc.
assert( &d == (offs + (size_t.sizeof * 2) * 4) );
}
--
In a second time I need to be sure that the return tuple of
the trait "allMembers" follow the declarations order. The
documentation says that:
"The order in which the strings appear in the result is not
defined".
But so far, it looks like it's ordered according to the
declaration (at least for a module containing only some global
variables).
Any other remarks about the topic are welcome.
Plese don't do this, it's undefined behavior and could make you
code invalid with a new compiler release or different compiler.
If possible use static arrays instead.
int[2] arr=[1,2];
@property auto ref b(){
return arr[1];
}
---
I've probably badly explained the what and the why. I ask this
because of this draft: http://dpaste.dzfl.pl/e15305cbc32d
Tool: generate a module with some static strings. (used as
ressources, e.g pictures, tables, etc.)
Manager: use the first item as base address since the other are
using the import expression.
Actually I don't get the sample you added to your answer, that
leads me to think that my initial Question is not well exposed.
Re: How the memory layout of global variable is reliable ?
On Thursday, 23 October 2014 at 08:04:23 UTC, ketmar via Digitalmars-d-learn wrote: On Thu, 23 Oct 2014 07:55:36 + Cjkp via Digitalmars-d-learn wrote: I've probably badly explained the what and the why. I ask this because of this draft: http://dpaste.dzfl.pl/e15305cbc32d Tool: generate a module with some static strings. (used as ressources, e.g pictures, tables, etc.) Manager: use the first item as base address since the other are using the import expression. Actually I don't get the sample you added to your answer, that leads me to think that my initial Question is not well exposed. why do you want all that voodoo? ain't it easier to make your tool generate something like "resource list array" too? Not wrong, I realize that I've been biased by being stubborn on my initial idea (which is: using the traits to link a member name to a pointer).
