Re: Meaning of iniline in declspec(dllexport)
On Fri, 30 Mar 2007 02:53:08 GMT, "David Ching" <dc@remove-this.dcsoft.com>
wrote:
"Doug Harrison [MVP]" <dsh@mvps.org> wrote in message
news:bc4o03h43d22tcdoq15of3pbg8cemdsn2h@4ax.com...
Below, the compiler ignores the import attribute and inlines X::f:
__declspec(dllimport) void g();
struct __declspec(dllimport) X
{
void f() { g(); }
};
void h(X& x)
{
x.f();
}
X>cl -O2 -FAs -c a.cpp
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 14.00.50727.762 for
80x86
?h@@YAXAAUX@@@Z PROC ; h, COMDAT
; 10 : x.f();
jmp DWORD PTR __imp_?g@@YAXXZ
?h@@YAXAAUX@@@Z ENDP ; h
If you change the imports to exports and compile a DLL, you will find the
compiler has exported X::f.
Sure, but there is no reason to export X::f() and g() if all you're going to
do is call them from within the same module in which they are defined!
Which is what you're illustrating with the generated code of h().
Uh, no. If it helps, pretend g and X came from a DLL header file that was
#included by a.cpp, and the macro that controls dllexport vs dllimport was
set to import. The file a.cpp would belong to a client of the DLL.The
result of preprocessing would look exactly like my example.
Now if you move h() to a different module and then show the generated code
to be the same thing, then I will truly be amazed that it is inlined.
You are hereby amazed. :)
Furthermore, most C++ programmers don't define the functions in the header
file as you have done here. And the header file is all that is available to
the compiler when it is compiling the different module containing h(). So I
don't see how it could generate inlined code for this reason anyway.
I guess you are proving the point that it is practically possible to have
both inline and __declspec(dllexport), but your explanation seems to defy
both common usage of exported functions and general C++ practice.
Really? You've never seen a class declared __declspec(dllexport) that had
even one member function defined inside the class body? You must hang with
a very disciplined bunch. Something else to consider are the
compiler-generated functions, the default ctor, copy ctor, assignment
operator, and dtor, which the compiler will generate as needed in client
code for exported classes. There's more to fully exporting classes than I
think most people probably realize...
--
Doug Harrison
Visual C++ MVP