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From: Igor Korot <ikorot01@gmail.com>
Date: Wed, 24 Dec 2025 17:28:23 -0800
Message-ID: <CA+FnnTzuJTaPBgzOyFxHJCCSqxvvOz7=LePnoonNQMepKT2DeA@mail.gmail.com>
Subject: Re: PQexecPrepared() question
To: pgsql-general@lists.postgresql.org
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Hi, ALL,
My current code is below:

    std::wstring query1 =3D L"SELECT t.table_catalog AS catalog,
t.table_schema AS schema, t.table_name AS table, u.usename AS owner,
c.oid AS table_id FROM information_schema.tables t,
pg_catalog.pg_class c, pg_catalog.pg_user u WHERE t.table_name =3D
c.relname AND c.relowner =3D usesysid AND (t.table_type =3D 'BASE TABLE'
OR t.table_type =3D 'VIEW' OR t.table_type =3D 'LOCAL TEMPORARY') ORDER BY
table_name;";
            std::wstring query7 =3D L"INSERT INTO \"abcattbl\" VALUES(
0, $1, (SELECT c.oid FROM pg_class c, pg_namespace nc WHERE nc.oid =3D
c.relnamespace AND c.relname =3D $2 AND nc.nspname =3D $3), \'\', 8, 400,
\'N\', \'N\', 0, 1, 0, \'MS Sans Serif\', 8, 400, \'N\', \'N\', 0, 1,
0, \'MS Sans Serif\', 8, 400, \'N\', \'N\', 0, 1, 0, \'MS Sans
Serif\', \'\' ) ON CONFLICT DO NOTHING;";
        for( int i =3D 0; i < PQntuples( res ) && !result; i++ )
         {
             std::wstring cat =3D m_pimpl->m_myconv.from_bytes(
PQgetvalue( res, i, 0 ) );
             std::wstring schema =3D m_pimpl->m_myconv.from_bytes(
PQgetvalue( res, i, 1 ) );
             std::wstring table =3D m_pimpl->m_myconv.from_bytes(
PQgetvalue( res, i, 2 ) );
             std::wstring  table_owner =3D m_pimpl->m_myconv.from_bytes(
PQgetvalue( res, i, 3 ) );
             pimpl.m_tableDefinitions[cat].push_back( TableDefinition(
cat, schema,  table ) );
             count++;
             paramValues =3D schema + L"." + table;
             params[0] =3D new char[paramValues.length() + 2];
             memset( params[0], '\0', paramValues.length() + 2 );
             auto temp =3D m_pimpl->m_myconv.to_bytes(
paramValues.c_str() ).c_str();
             params[0] =3D const_cast<char *>(
m_pimpl->m_myconv.to_bytes( paramValues.c_str() ).c_str() );
             params[1] =3D new char[table.length() + 2];
             memset( params[1], '\0', table.length() + 2 );
             params[1] =3D const_cast<char *>(
m_pimpl->m_myconv.to_bytes( table.c_str() ).c_str() );
             params[2] =3D new char[table_owner.length() + 2];
             memset( params[2], '\0', table_owner.length() + 2 );
             params[2] =3D const_cast<char *>(
m_pimpl->m_myconv.to_bytes( table_owner.c_str() ).c_str() );
             paramFormat[0] =3D paramFormat[1] =3D paramFormat[2] =3D 0;
             paramLength[0] =3D paramValues.length();
             paramLength[1] =3D table.length();
             paramLength[2] =3D table_owner.length();
             res8 =3D PQexecPrepared( m_db, "set_table_prop", 3, params,
paramLength, paramFormat, 0 );
             if( PQresultStatus( res8 ) !=3D PGRES_COMMAND_OK )
             {
                 std::wstring err =3D m_pimpl->m_myconv.from_bytes(
PQerrorMessage( m_db ) );
                 errorMsg.push_back( L"Error executing query: " + err );
                 result =3D 1;
             }
             PQclear( res8 );
             delete[] params[0];
             params[0] =3D nullptr;
             delete[] params[1];
             params[1] =3D nullptr;
             delete[] params[2];
             params[2] =3D nullptr;
         }

This code crashes on the PQexecParam.

I am completely puzzled.

Could anyone help?

Thank you.


On Mon, Dec 22, 2025 at 3:07=E2=80=AFPM Igor Korot <ikorot01@gmail.com> wro=
te:
>
> Hi, Peter,
>
> On Mon, Dec 22, 2025 at 1:55=E2=80=AFAM Peter J. Holzer <hjp-pgsql@hjp.at=
> wrote:
> >
> > On 2025-12-21 17:30:38 -0800, Igor Korot wrote:
> > > On Sun, Dec 21, 2025 at 1:19=E2=80=AFPM Peter J. Holzer <hjp-pgsql@hj=
p.at> wrote:
> > > > As I see it, Igor has two options:
> > > >
> > > > 1) Send UTF8. wcstombs is the wrong tool for this, since it uses th=
e
> > > >    current locale which is obviously not using UTF-8. I don't progr=
am in
> > > >    C++, but I'm pretty sure there is a portable way to encode a str=
ing
> > > >    in UTF-8.
> > [...]
> > > > I think 1) is the better strategy, but them I've been a UTF-8 fan-b=
oy
> > > > for over 30 years ;-).
> > >
> > > Maybe all I need is something like this:
> > >
> > > convert(char *dest, const std::wstring src)
> > > {
> > >     const wchar_t *temp =3D src.c_str();
> > >     while( *dest )
> > >     {
> > >         dest++;
> > >     }
> > >     while( *temp )
> > >     {
> > >         *dest =3D *temp;
> > >         dest++;
> > >         temp++;
> > >     }
> > >     *dest++ =3D '\0';
> > >     *dest =3D '\0';
> > > }
> > >
> > > ?
> >
> > I hope your compiler complains loudly about that code. You can't just
> > assign a wchar_t to a char and expect it to do anything sensible.
>
> At least MSVC 2017 did not.
> However, trying didn't solve it. Same error.
>
> >
> > A short search points to std::wstring_convert, but that has been
> > deprecated in C++17, and it's not obvious to me what the replacement is=
.
> >
> > There is always ICU, of course, but that feels like cracking a nut with
> > a sledgehammer.
>
> I think ICU IS a replacement for wstring_comvert.
> Will check it.
>
> >
> > Personally, I might roll my own if an hour of googling doesn't turn up
> > anything promising (UTF-8 encoding is quite simple), but that shouldn't
> > be necessary.
> >
> >
> >         hjp
> >
> > --
> >    _  | Peter J. Holzer    | Story must make more sense than reality.
> > |_|_) |                    |
> > | |   | hjp@hjp.at         |    -- Charles Stross, "Creative writing
> > __/   | http://www.hjp.at/ |       challenge!"