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From: Dominique Devienne <[email protected]>
To: Igor Korot <[email protected]>
Cc: pgsql-generallists.postgresql.org <[email protected]>
Subject: Re: libpq usage from C++
Date: Mon, 16 Mar 2026 11:25:15 +0100
Message-ID: <CAFCRh-8+GXA+j0qyccc+Yj3TWZy7Uy1v8V_ohqC8D9u7+j3ZUg@mail.gmail.com> (raw)
In-Reply-To: <CA+FnnTzfegG8E3JoB0P9cFMZLS2__+0ZtixyGHtxxmSXKk=o6A@mail.gmail.com>
References: <CA+FnnTzfegG8E3JoB0P9cFMZLS2__+0ZtixyGHtxxmSXKk=o6A@mail.gmail.com>

On Sat, Mar 14, 2026 at 5:41 AM Igor Korot <[email protected]> wrote:
> Does anybody use libpq from C++?

Yes

> C++ introduces STL.
> C++ introduces smart-pointers.
> Is there a simple way of using those writing libpq communication?
> Or should I just forget about them and use good old "dump pointers"?

Using an existing wrapper is simplest, of course.
We wrote our own. To each its own. E.g.

PS: Avoid the fwd-decl by using the actual libpq headers instead.

extern "C" {

struct pg_conn;
struct pg_result;
typedef struct pg_conn PGconn;
typedef struct pg_result PGresult;
typedef struct _PQconninfoOption PQconninfoOption;
typedef struct pgNotify PGnotify;
void PQfreemem(void *ptr);
void PQclear(PGresult* res);
void PQfinish(PGconn* conn);
void PQconninfoFree(PQconninfoOption* conn);

} // extern "C"

namespace acme::postgresql {

struct PGDeleterFunctor {
    void operator()(PGresult* r) {
        if (r != nullptr) {
            PQclear(r);
        }
    }
    void operator()(PGconn* c) {
        if (c != nullptr) {
            PQfinish(c);
        }
    }
    void operator()(PQconninfoOption* c) {
        if (c != nullptr) {
            PQconninfoFree(c);
        }
    }
    void operator()(PGnotify* n) {
        if (n != nullptr) {
            PQfreemem(n);
        }
    }
};
using PGresult_uptr     = std::unique_ptr<PGresult,         PGDeleterFunctor>;
using PGconn_uptr       = std::unique_ptr<PGconn,           PGDeleterFunctor>;
using PGconninfo_uptr   = std::unique_ptr<PQconninfoOption, PGDeleterFunctor>;
using PGnotify_uptr     = std::unique_ptr<PGnotify,         PGDeleterFunctor>;

...
}

Then we have higher-level wrappers that compose those RAII low-level ones. --DD

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