Is any support for reworking the postgres headers such that they can be used,
cleanly, in a C++ program?

Sat, 19 May 2001 10:21:27 -0400
mlw <markw@mohawksoft.com>
C++ Headers

My guess it that certain defines have to be #ifdef'ed out for C++.  Can
you list them again.  We have talked about this in the past, but haven't
gotten a solution yet.

> Is any support for reworking the postgres headers such that they can be used,
> cleanly, in a C++ program?
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 4: Don't 'kill -9' the postmaster
> 

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

Sat, 19 May 2001 11:25:11 -0400 (EDT)
Bruce Momjian <pgman@candle.pha.pa.us>
Re: C++ Headers
mlw <markw@mohawksoft.com> writes:
> Is any support for reworking the postgres headers such that they can be used,
> cleanly, in a C++ program?

You'll get no support for a request for a blank check.  What do you have
in mind exactly?

ISTM that making the backend's internal headers C++-clean has already
been looked into, but rejected on grounds that I don't recall clearly.
Check the list archives.

			regards, tom lane

Sat, 19 May 2001 11:26:29 -0400
Tom Lane <tgl@sss.pgh.pa.us>
Re: C++ Headers 
* Tom Lane <tgl@sss.pgh.pa.us> [010519 10:29]:
> mlw <markw@mohawksoft.com> writes:
> > Is any support for reworking the postgres headers such that they can be used,
> > cleanly, in a C++ program?
> 
> You'll get no support for a request for a blank check.  What do you have
> in mind exactly?
> 
> ISTM that making the backend's internal headers C++-clean has already
> been looked into, but rejected on grounds that I don't recall clearly.
> Check the list archives.
I do know that you can use libpq-fe.h cleanly in a C++ program (the 
table posted earlier today gets populated by a C++ app), modulo the
Oid type conflicts with an SNMP++ header, handled by a quick #define. 

LER

> 
> 			regards, tom lane
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 4: Don't 'kill -9' the postmaster
> 

-- 
Larry Rosenman                     http://www.lerctr.org/~ler
Phone: +1 972-414-9812                 E-Mail: ler@lerctr.org
US Mail: 1905 Steamboat Springs Drive, Garland, TX 75044-6749

Sat, 19 May 2001 11:04:37 -0500
Larry Rosenman <ler@lerctr.org>
Re: C++ Headers
Tom Lane wrote:

> mlw <markw@mohawksoft.com> writes:
> > Is any support for reworking the postgres headers such that they can be used,
> > cleanly, in a C++ program?
>
> You'll get no support for a request for a blank check.  What do you have
> in mind exactly?
>
> ISTM that making the backend's internal headers C++-clean has already
> been looked into, but rejected on grounds that I don't recall clearly.
> Check the list archives.
>

I have used:

    #ifdef __cplusplus
    extern "C" {
    #endif

    headers......



    #ifdef __cplusplus
    }
    #endif


on many backend header files for use
on my threaded version of postgres.
I seems to work fine as I have not had any problems
yet.


Myron Scott





Sat, 19 May 2001 10:09:59 -0700
Myron Scott <mscott@sacadia.com>
Re: C++ Headers
> Tom Lane wrote:
> 
> > mlw <markw@mohawksoft.com> writes:
> > > Is any support for reworking the postgres headers such that they can be used,
> > > cleanly, in a C++ program?
> >
> > You'll get no support for a request for a blank check.  What do you have
> > in mind exactly?
> >
> > ISTM that making the backend's internal headers C++-clean has already
> > been looked into, but rejected on grounds that I don't recall clearly.
> > Check the list archives.
> >
> 
> I have used:
> 
>     #ifdef __cplusplus
>     extern "C" {
>     #endif
> 
>     headers......
> 
> 
> 
>     #ifdef __cplusplus
>     }
>     #endif
> 
> 
> on many backend header files for use
> on my threaded version of postgres.
> I seems to work fine as I have not had any problems
> yet.

The only mention I see of this is in c.h:
	
	#ifndef __cplusplus
	#ifndef bool
	typedef char bool;
	
	#endif   /* ndef bool */
	#endif   /* not C++ */

If you need more cplusplus stuff, lets figure it out and add it.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

Sat, 19 May 2001 13:17:10 -0400 (EDT)
Bruce Momjian <pgman@candle.pha.pa.us>
Re: C++ Headers
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> The only mention I see of this is in c.h:
	
> 	#ifndef __cplusplus
> 	#ifndef bool
> 	typedef char bool;
	
> 	#endif   /* ndef bool */
> 	#endif   /* not C++ */

> If you need more cplusplus stuff, lets figure it out and add it.

Actually, that portion of c.h is a time bomb that is likely to blow up
in the face of some poor C++ user.  There's no guarantee that a C++
compiler's built-in bool type will be compatible with "char", is there?
If it happened to be, say, same size as "int", then a C++ module
would interpret lots of things differently from a C module.

			regards, tom lane

Sat, 19 May 2001 20:34:22 -0400
Tom Lane <tgl@sss.pgh.pa.us>
Re: C++ Headers 
Tom Lane wrote:

> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > The only mention I see of this is in c.h:
>
> >       #ifndef __cplusplus
> >       #ifndef bool
> >       typedef char bool;
>
> >       #endif   /* ndef bool */
> >       #endif   /* not C++ */
>
> > If you need more cplusplus stuff, lets figure it out and add it.
>
> Actually, that portion of c.h is a time bomb that is likely to blow up
> in the face of some poor C++ user.  There's no guarantee that a C++
> compiler's built-in bool type will be compatible with "char", is there?
> If it happened to be, say, same size as "int", then a C++ module
> would interpret lots of things differently from a C module.

This in fact has happened within ECPG. But since sizeof(bool) is passed to
libecpg it was possible to figure out which 'bool' is requested.

Another issue of C++ compatibility would be cleaning up the usage of
'const' declarations. C++ is really strict about 'const'ness. But I don't
know whether postgres' internal headers would need such a cleanup. (I
suspect that in ecpg there is an oddity left with respect to host variable
declaration. I'll check that later)

    Christof



Mon, 21 May 2001 11:01:01 +0200
Christof Petig <christof@petig-baender.de>
Re: C++ Headers
> This in fact has happened within ECPG. But since sizeof(bool) is passed to
> libecpg it was possible to figure out which 'bool' is requested.
> 
> Another issue of C++ compatibility would be cleaning up the usage of
> 'const' declarations. C++ is really strict about 'const'ness. But I don't
> know whether postgres' internal headers would need such a cleanup. (I
> suspect that in ecpg there is an oddity left with respect to host variable
> declaration. I'll check that later)

We have added more const-ness to libpq++ for 7.2.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

Tue, 22 May 2001 00:19:41 -0400 (EDT)
Bruce Momjian <pgman@candle.pha.pa.us>
Re: C++ Headers
On Tue, May 22, 2001 at 12:19:41AM -0400, Bruce Momjian wrote:
> > This in fact has happened within ECPG. But since sizeof(bool) is passed to
> > libecpg it was possible to figure out which 'bool' is requested.
> > 
> > Another issue of C++ compatibility would be cleaning up the usage of
> > 'const' declarations. C++ is really strict about 'const'ness. But I don't
> > know whether postgres' internal headers would need such a cleanup. (I
> > suspect that in ecpg there is an oddity left with respect to host variable
> > declaration. I'll check that later)
> 
> We have added more const-ness to libpq++ for 7.2.

Breaking link compatibility without bumping the major version number
on the library seems to me serious no-no.

To const-ify member functions without breaking link compatibility,
you have to add another, overloaded member that is const, and turn
the non-const function into a wrapper.  For example:

  void Foo::bar() { ... }   // existing interface

becomes

  void Foo::bar() { ((const Foo*)this)->bar(); }   
  void Foo::bar() const { ... }   

Nathan Myers
ncm@zembu.com

Tue, 22 May 2001 13:34:58 -0700
ncm@zembu.com (Nathan Myers)
Re: C++ Headers
> On Tue, May 22, 2001 at 12:19:41AM -0400, Bruce Momjian wrote:
> > > This in fact has happened within ECPG. But since sizeof(bool) is passed to
> > > libecpg it was possible to figure out which 'bool' is requested.
> > > 
> > > Another issue of C++ compatibility would be cleaning up the usage of
> > > 'const' declarations. C++ is really strict about 'const'ness. But I don't
> > > know whether postgres' internal headers would need such a cleanup. (I
> > > suspect that in ecpg there is an oddity left with respect to host variable
> > > declaration. I'll check that later)
> > 
> > We have added more const-ness to libpq++ for 7.2.
> 
> Breaking link compatibility without bumping the major version number
> on the library seems to me serious no-no.
> 
> To const-ify member functions without breaking link compatibility,
> you have to add another, overloaded member that is const, and turn
> the non-const function into a wrapper.  For example:
> 
>   void Foo::bar() { ... }   // existing interface
> 
> becomes
> 
>   void Foo::bar() { ((const Foo*)this)->bar(); }   
>   void Foo::bar() const { ... }   

Thanks.  That was my problem, not knowing when I break link compatiblity
in C++.  Major updated.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

Tue, 22 May 2001 17:52:20 -0400 (EDT)
Bruce Momjian <pgman@candle.pha.pa.us>
Re: C++ Headers
On Tue, May 22, 2001 at 05:52:20PM -0400, Bruce Momjian wrote:
> > On Tue, May 22, 2001 at 12:19:41AM -0400, Bruce Momjian wrote:
> > > > This in fact has happened within ECPG. But since sizeof(bool) is
> > > > passed to libecpg it was possible to figure out which 'bool' is
> > > > requested.
> > > >
> > > > Another issue of C++ compatibility would be cleaning up the
> > > > usage of 'const' declarations. C++ is really strict about
> > > > 'const'ness. But I don't know whether postgres' internal headers
> > > > would need such a cleanup. (I suspect that in ecpg there is an
> > > > oddity left with respect to host variable declaration. I'll
> > > > check that later)
> > >
> > > We have added more const-ness to libpq++ for 7.2.
> > 
> > Breaking link compatibility without bumping the major version number
> > on the library seems to me serious no-no.
> > 
> > To const-ify member functions without breaking link compatibility,
> > you have to add another, overloaded member that is const, and turn
> > the non-const function into a wrapper.  For example:
> > 
> >   void Foo::bar() { ... }   // existing interface
> > 
> > becomes
> > 
> >   void Foo::bar() { ((const Foo*)this)->bar(); }   
> >   void Foo::bar() const { ... }   
> 
> Thanks.  That was my problem, not knowing when I break link compatiblity
> in C++.  Major updated.

Wouldn't it be better to add the forwarding function and keep
the same major number?  It's quite disruptive to change the
major number for what are really very minor changes.  Otherwise
you accumulate lots of near-copies of almost-identical libraries
to be able to run old binaries.

A major-number bump should usually be something planned for
and scheduled.

Nathan Myers
ncm@zembu.com

Tue, 22 May 2001 18:27:19 -0700
ncm@zembu.com (Nathan Myers)
Re: C++ Headers
> > > > We have added more const-ness to libpq++ for 7.2.
> > > 
> > > Breaking link compatibility without bumping the major version number
> > > on the library seems to me serious no-no.
> > > 
> > > To const-ify member functions without breaking link compatibility,
> > > you have to add another, overloaded member that is const, and turn
> > > the non-const function into a wrapper.  For example:
> > > 
> > >   void Foo::bar() { ... }   // existing interface
> > > 
> > > becomes
> > > 
> > >   void Foo::bar() { ((const Foo*)this)->bar(); }   
> > >   void Foo::bar() const { ... }   
> > 
> > Thanks.  That was my problem, not knowing when I break link compatiblity
> > in C++.  Major updated.
> 
> Wouldn't it be better to add the forwarding function and keep
> the same major number?  It's quite disruptive to change the
> major number for what are really very minor changes.  Otherwise
> you accumulate lots of near-copies of almost-identical libraries
> to be able to run old binaries.
> 
> A major-number bump should usually be something planned for
> and scheduled.

That const was just one of many const's added, and I am sure there will
be more stuff happening to C++.  I changed a function returning short
for tuple length to int.  Not worth mucking it up.

If it was just that one it would be OK.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

Wed, 23 May 2001 11:35:31 -0400 (EDT)
Bruce Momjian <pgman@candle.pha.pa.us>
Re: C++ Headers