Re: BUG #6216: Calling PQconnectdbParams from C++ with a char**

On Tue, Sep 20, 2011 at 11:05 AM, Lionel Elie Mamane <lionel@mamane.lu> wro=
te:
>
> The following bug has been logged online:
>
> Bug reference: =A0 =A0 =A06216
> Logged by: =A0 =A0 =A0 =A0 =A0Lionel Elie Mamane
> Email address: =A0 =A0 =A0lionel@mamane.lu
> PostgreSQL version: 9.1.0
> Operating system: =A0 Debian GNU/Linux
> Description: =A0 =A0 =A0 =A0Calling PQconnectdbParams from C++ with a cha=
r**
> Details:
>
> In C++, a "char**" value is not convertible to a "const char**" value,
> because that is not safe (see
> http://www.parashift.com/c++-faq-lite/const-correctness.html#faq-18.17).
>
> This means one cannot call libpq's PQconnectdbParams and friends passing
> them a "char**" value for keywords and/or values, as these arguments are
> declared "const char**".
>
> So please apply this patch, which declares them "char const* const*"
> instead, which is:
> =A0- equivalent to "const char * const*"; use that one if you prefer
> =A0- still true, since libpq won't write to they keyword/values arrays
> =A0- allows to pass a "char**" to them and be recognised by a C++ compile=
r as
> OK without a cast.
>
> This patch is licensed under a "do whatever you want with it" license.
>
> Thanks in advance.
>
>
> --- postgresql-9.1-9.1.0.orig/src/interfaces/libpq/fe-connect.c
> +++ postgresql-9.1-9.1.0/src/interfaces/libpq/fe-connect.c
> @@ -291,8 +291,8 @@ static void freePGconn(PGconn *conn);
> =A0static void closePGconn(PGconn *conn);
> =A0static PQconninfoOption *conninfo_parse(const char *conninfo,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 PQExpBuffer errorMess=
age, bool use_defaults);
> -static PQconninfoOption *conninfo_array_parse(const char **keywords,
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0const char **values, PQExpBuffer errorMessage,
> +static PQconninfoOption *conninfo_array_parse(char const* const*keywords,
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0char const* const*values, PQExpBuffer errorMessage,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 bool use_defaults, int expand_dbname);
> =A0static char *conninfo_getval(PQconninfoOption *connOptions,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0const char=
 *keyword);
> @@ -362,8 +362,8 @@ pgthreadlock_t pg_g_threadlock =3D default
> =A0* call succeeded.
> =A0*/
> =A0PGconn *
> -PQconnectdbParams(const char **keywords,
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 const c=
har **values,
> +PQconnectdbParams(char const* const*keywords,
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 char co=
nst* const*values,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0int ex=
pand_dbname)
> =A0{
> =A0 =A0 =A0 =A0PGconn =A0 =A0 *conn =3D PQconnectStartParams(keywords, va=
lues, expand_dbname);
> @@ -381,8 +381,8 @@ PQconnectdbParams(const char **keywords,
> =A0* check server status, accepting parameters identical to
> PQconnectdbParams
> =A0*/
> =A0PGPing
> -PQpingParams(const char **keywords,
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0const char **values,
> +PQpingParams(char const* const*keywords,
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0char const* const*values,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 int expand_dbname)
> =A0{
> =A0 =A0 =A0 =A0PGconn =A0 =A0 *conn =3D PQconnectStartParams(keywords, va=
lues, expand_dbname);
> @@ -464,8 +464,8 @@ PQping(const char *conninfo)
> =A0* See PQconnectPoll for more info.
> =A0*/
> =A0PGconn *
> -PQconnectStartParams(const char **keywords,
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0const char **values,
> +PQconnectStartParams(char const* const*keywords,
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0char const* const*values,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 int expand_dbname)
> =A0{
> =A0 =A0 =A0 =A0PGconn =A0 =A0 *conn;
> @@ -4249,7 +4249,7 @@ conninfo_parse(const char *conninfo, PQE
> =A0* keywords will take precedence, however.
> =A0*/
> =A0static PQconninfoOption *
> -conninfo_array_parse(const char **keywords, const char **values,
> +conninfo_array_parse(char const* const*keywords, char const* const*value=
s,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 PQExpBuffer errorMessage, bool use_defaults,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 int expand_dbname)
> =A0{
> --- postgresql-9.1-9.1.0.orig/src/interfaces/libpq/libpq-fe.h
> +++ postgresql-9.1-9.1.0/src/interfaces/libpq/libpq-fe.h
> @@ -235,14 +235,14 @@ typedef struct pgresAttDesc
> =A0/* make a new client connection to the backend */
> =A0/* Asynchronous (non-blocking) */
> =A0extern PGconn *PQconnectStart(const char *conninfo);
> -extern PGconn *PQconnectStartParams(const char **keywords,
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0const char **values, int expand_dbname);
> +extern PGconn *PQconnectStartParams(char const* const*keywords,
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0char const* const*values, int expand_dbname);
> =A0extern PostgresPollingStatusType PQconnectPoll(PGconn *conn);
>
> =A0/* Synchronous (blocking) */
> =A0extern PGconn *PQconnectdb(const char *conninfo);
> -extern PGconn *PQconnectdbParams(const char **keywords,
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 const c=
har **values, int expand_dbname);
> +extern PGconn *PQconnectdbParams(char const* const*keywords,
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 char co=
nst* const*values, int expand_dbname);
> =A0extern PGconn *PQsetdbLogin(const char *pghost, const char *pgport,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 const char *pgoptions, co=
nst char *pgtty,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 const char *dbName,
> @@ -413,8 +413,8 @@ extern int =A0PQsetnonblocking(PGconn *conn
> =A0extern int =A0 =A0 PQisnonblocking(const PGconn *conn);
> =A0extern int =A0 =A0 PQisthreadsafe(void);
> =A0extern PGPing PQping(const char *conninfo);
> -extern PGPing PQpingParams(const char **keywords,
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0const char **values, int=
 expand_dbname);
> +extern PGPing PQpingParams(char const* const*keywords,
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0char const* const*values=
, int expand_dbname);
>
> =A0/* Force the write buffer to be written (or at least try) */
> =A0extern int =A0 =A0 PQflush(PGconn *conn);

I agree with the rationale.  Note query parameter arguments are
already declared this way.

merlin