C++ Headers

Started by mlwalmost 25 years ago15 messageshackers

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mlw

markw@mohawksoft.com

almost 25 years ago

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

Bruce Momjian

bruce@momjian.us

almost 25 years ago

In reply to: mlw (#1)

Re: 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?

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-- 
  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

Tom Lane

tgl@sss.pgh.pa.us

almost 25 years ago

In reply to: mlw (#1)

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

Larry Rosenman

ler@lerctr.org

almost 25 years ago

In reply to: Tom Lane (#3)

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

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Larry Rosenman http://www.lerctr.org/~ler
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US Mail: 1905 Steamboat Springs Drive, Garland, TX 75044-6749

Myron Scott

mscott@sacadia.com

almost 25 years ago

In reply to: mlw (#1)

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

Bruce Momjian

bruce@momjian.us

almost 25 years ago

In reply to: Myron Scott (#5)

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

Tom Lane

tgl@sss.pgh.pa.us

almost 25 years ago

In reply to: Bruce Momjian (#6)

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

Christof Petig

christof@petig-baender.de

almost 25 years ago

In reply to: Bruce Momjian (#6)

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

Bruce Momjian

bruce@momjian.us

almost 25 years ago

In reply to: Christof Petig (#8)

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

#10

Nathan Myers

ncm@zembu.com

almost 25 years ago

In reply to: Bruce Momjian (#9)

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

#11

Bruce Momjian

bruce@momjian.us

almost 25 years ago

In reply to: Nathan Myers (#10)

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

#12

Nathan Myers

ncm@zembu.com

almost 25 years ago

In reply to: Bruce Momjian (#11)

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

#13

Bruce Momjian

bruce@momjian.us

almost 25 years ago

In reply to: Nathan Myers (#12)

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

#14

Nathan Myers

ncm@zembu.com

almost 25 years ago

In reply to: Bruce Momjian (#13)

Re: C++ Headers

On Wed, May 23, 2001 at 11:35:31AM -0400, Bruce Momjian wrote:

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.

I'll bet lots of people would like to see more careful planning about
breaking link compatibility. Other changes that break link compatibility
include changing a struct or class referred to from inline functions, and
adding a virtual function in a base class.

It's possible to make a lot of improvements without breaking link
compatibility, but it does take more care than in C. If you wonder
whether a change would break link compatibility, please ask on the list.

Nathan Myers
ncm@zembu.com

Import Notes

Resolved by subject fallback

#15

Bruce Momjian

bruce@momjian.us

almost 25 years ago

In reply to: Nathan Myers (#14)

Re: C++ Headers

If it was just that one it would be OK.

I'll bet lots of people would like to see more careful planning about
breaking link compatibility. Other changes that break link compatibility
include changing a struct or class referred to from inline functions, and
adding a virtual function in a base class.

It's possible to make a lot of improvements without breaking link
compatibility, but it does take more care than in C. If you wonder
whether a change would break link compatibility, please ask on the list.

Our C++ interface needs serious work, and I don't want to burden a
maintainer with adding muck for backward compatibility.

We do update libpq occasionally and don't keep link compatibility. We do
keep interface compatibility with the backend.

-- 
  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