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

On Tue, Sep 20, 2011 at 11:05 AM, Lionel Elie Mamane <lionel(at)mamane(dot)lu> wrote:
>
> The following bug has been logged online:
>
> Bug reference:      6216
> Logged by:          Lionel Elie Mamane
> Email address:      lionel(at)mamane(dot)lu
> PostgreSQL version: 9.1.0
> Operating system:   Debian GNU/Linux
> Description:        Calling PQconnectdbParams from C++ with a char**
> 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:
>  - equivalent to "const char * const*"; use that one if you prefer
>  - still true, since libpq won't write to they keyword/values arrays
>  - allows to pass a "char**" to them and be recognised by a C++ compiler 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);
>  static void closePGconn(PGconn *conn);
>  static PQconninfoOption *conninfo_parse(const char *conninfo,
>                           PQExpBuffer errorMessage, bool use_defaults);
> -static PQconninfoOption *conninfo_array_parse(const char **keywords,
> -                                        const char **values, PQExpBuffer errorMessage,
> +static PQconninfoOption *conninfo_array_parse(char const* const*keywords,
> +                                        char const* const*values, PQExpBuffer errorMessage,
>                                         bool use_defaults, int expand_dbname);
>  static char *conninfo_getval(PQconninfoOption *connOptions,
>                                const char *keyword);
> @@ -362,8 +362,8 @@ pgthreadlock_t pg_g_threadlock = default
>  * call succeeded.
>  */
>  PGconn *
> -PQconnectdbParams(const char **keywords,
> -                                 const char **values,
> +PQconnectdbParams(char const* const*keywords,
> +                                 char const* const*values,
>                                  int expand_dbname)
>  {
>        PGconn     *conn = PQconnectStartParams(keywords, values, expand_dbname);
> @@ -381,8 +381,8 @@ PQconnectdbParams(const char **keywords,
>  * check server status, accepting parameters identical to
> PQconnectdbParams
>  */
>  PGPing
> -PQpingParams(const char **keywords,
> -                        const char **values,
> +PQpingParams(char const* const*keywords,
> +                        char const* const*values,
>                         int expand_dbname)
>  {
>        PGconn     *conn = PQconnectStartParams(keywords, values, expand_dbname);
> @@ -464,8 +464,8 @@ PQping(const char *conninfo)
>  * See PQconnectPoll for more info.
>  */
>  PGconn *
> -PQconnectStartParams(const char **keywords,
> -                                        const char **values,
> +PQconnectStartParams(char const* const*keywords,
> +                                        char const* const*values,
>                                         int expand_dbname)
>  {
>        PGconn     *conn;
> @@ -4249,7 +4249,7 @@ conninfo_parse(const char *conninfo, PQE
>  * keywords will take precedence, however.
>  */
>  static PQconninfoOption *
> -conninfo_array_parse(const char **keywords, const char **values,
> +conninfo_array_parse(char const* const*keywords, char const* const*values,
>                                         PQExpBuffer errorMessage, bool use_defaults,
>                                         int expand_dbname)
>  {
> --- 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
>  /* make a new client connection to the backend */
>  /* Asynchronous (non-blocking) */
>  extern PGconn *PQconnectStart(const char *conninfo);
> -extern PGconn *PQconnectStartParams(const char **keywords,
> -                                        const char **values, int expand_dbname);
> +extern PGconn *PQconnectStartParams(char const* const*keywords,
> +                                        char const* const*values, int expand_dbname);
>  extern PostgresPollingStatusType PQconnectPoll(PGconn *conn);
>
>  /* Synchronous (blocking) */
>  extern PGconn *PQconnectdb(const char *conninfo);
> -extern PGconn *PQconnectdbParams(const char **keywords,
> -                                 const char **values, int expand_dbname);
> +extern PGconn *PQconnectdbParams(char const* const*keywords,
> +                                 char const* const*values, int expand_dbname);
>  extern PGconn *PQsetdbLogin(const char *pghost, const char *pgport,
>                         const char *pgoptions, const char *pgtty,
>                         const char *dbName,
> @@ -413,8 +413,8 @@ extern int  PQsetnonblocking(PGconn *conn
>  extern int     PQisnonblocking(const PGconn *conn);
>  extern int     PQisthreadsafe(void);
>  extern PGPing PQping(const char *conninfo);
> -extern PGPing PQpingParams(const char **keywords,
> -                        const char **values, int expand_dbname);
> +extern PGPing PQpingParams(char const* const*keywords,
> +                        char const* const*values, int expand_dbname);
>
>  /* Force the write buffer to be written (or at least try) */
>  extern int     PQflush(PGconn *conn);

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

merlin