Re: Why PGDLLIMPORT is needed

On 10/29/2012 02:05 PM, 高健 wrote:
> On /src/include/storage/proc.h:
>
> I saw the following line:
>
> extern PGDLLIMPORT PGPROC *MyProc;
>
> I want to know why PGDLLIMPORT is used here?
>
> Does it mean: exten PGPROC *MyProc;  right?

What platform are you working on?

On Windows it's required to allow the static linker to generate the
correct symbol tables and the runtime/dynamic linker to correctly link
binaries. See:

http://support.microsoft.com/kb/132044
http://msdn.microsoft.com/en-us/library/8fskxacy(v=vs.80).aspx
http://msdn.microsoft.com/en-us/library/a90k134d(v=vs.80).aspx

For other platforms the same macros can be used for symbol visibility
filtering, but are usually set to evaluate to nothing so they have no
effect.

"extern" is always implicit for a prototype in a header, so while that
declaration does mean "extern PGPROC *MyPRoc;" that's nothing to do with
the PGDLLIMPORT macro.

--
Craig Ringer