For Windows, that supports both ordinal and named exports, the advantage
of ordinal export is faster linkage and harder reverse-engineering.
With named exports, it is quite easy to look at a DLL and find out what
services it exports - you still need to find out parameter types etc.
When exporting a c++ symbol by name, the fully decorated name must be
specified. The advantage is that you then get type-safe linkage even when
using DLL files. Obviously, by defining the symbol as extern "C", it won't
use any name mangling, so it is a lot easier to create the def file. With
"C" linkage, it is also easier to interact between different compilers,
since it doesn't matter if they use different name-mangling rules.
However, they still have to use the same calling conventions.
/Per W
On Tue, 9 Sep 2003, P.D. van Zelst wrote:
> Well, it's a number you can define yourself... you can give it any
> arbitrary value. If it was something critical as the stack size for
> example, I don't think they'd let you specify it yourself. The numbers
> in the .def files (after the @ symbol) get put there by the developers
> who create the DLL, not by the compiler.
> And now I know the reason why you can use these numbers as well....
> here's an excerpt from a webpage I found:
>
> "Module definition file
> In conventional systems, DLLs may export by name or by ordinal. Symbian
> OS only supports exporting by ordinal. Exporting by ordinal reduces the
> time taken to find the item in the DLL export table and also reduces the
> size of the DLL as names need not be stored. Ordinals are used for
> accessing the address of a function in the DLL export table.
>
> A module definition file (.def) is a text file which lists the exported
> functions of a DLL; it is used in an ordinal build to insert ordinal
> information into the DLL export table."
>
> Don't know if this holds exactly true for all .def files, since this is
> from the Symbian website, but it's a start :)
>
> -----Original Message-----
> From: dev...@li...
> [mailto:dev...@li...] On Behalf Of OROSZI
> Bal=E1zs
> Sent: Monday, September 08, 2003 9:47 PM
> To: dev...@li...
> Subject: Re: [Dev-C++] @ symbol at the end of function names?
>
>
> P.D. van Zelst wrote:
> > The @ symbol in .def files has nothing to do with name mangling, stack
>
> > sizes, or whatever. They're ordinal numbers you can optionally give to
>
> > the functions you export from the DLL. Don't know the exact use of
> > those though.... never had to look it up, I just always put them in
> > there out of habit :)
>
> Are you sure? I thought it was stack size. Somehow, I think it is stack
> size, as if a funcion takes 1 int, then the number is 4, if takes 2
> ints, then the number is 8, if 3 ints, it is 12. That looks like a
> pattern for sure.
>
> --
> Greetings,
> Bal=E1zs
>
>
>
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