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Re: Mostly Harmless: c++bookends - patch 2 of 4

From: Kurt Harriman <harriman(at)acm(dot)org>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Mostly Harmless: c++bookends - patch 2 of 4
Date: 2008-12-05 09:16:37
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
(Re-sending just the second of four patches: c++bookends)

These patches are based on CVS head in which the latest commit was
  user:        petere
  date:        Thu Dec 04 17:51:28 2008 +0000
  summary:     Default values for function arguments

2. c++bookends

     C++ code can call C functions and share global variables with C,
     provided those declarations are surrounded by "bookends":

         extern "C" {

     Header files can be made bilingual, to declare interfaces which
     look the same to both C and C++ callers.  This is done by
     placing C++ bookends within the header file, guarded by #ifdefs

         #ifdef __cplusplus
         extern "C" {
         #ifdef __cplusplus
         }; /* extern "C" */

     This way the C++ caller can just #include the header file without
     worrying whether the interface is implemented in C or C++.

     Usually, extension modules written in C++ will put bookends around
     all of their PostgreSQL #includes.

     However, "postgres.h" usually stands alone as the first #include,
     followed by some system #includes, and then the rest of the
     PostgreSQL #includes.  It is much nicer if a C++ file has just one
     pair of bookends around its main block of PostgreSQL #includes.
     This patch gives postgres.h its own internal bookends, making it
     bilingual, so that its #include can continue to stand alone at the
     head of each file.

     Just a few additional header files are mentioned in the PostgreSQL
     Reference Manual for add-on developers to use: fmgr.h, funcapi.h,
     and spi.h.  This patch adds bookends within those three files for
     the benefit of beginners writing very simple extensions in C++.
     Documentation and learning are simplified because C example code
     can be compiled as C or C++ without change.

Attachment: c++bookends.patch
Description: text/plain (2.0 KB)

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