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Thread: libpq-fe: PQgetvalue() ?

libpq-fe: PQgetvalue() ?

From
sad
Date:
hi

does PQgetvalue() allocate memory rof its result, it returns ?
the answer will help me in problem:
should i free some cstring_variable if
{ cstring_variable=PQgetvalue(pgresult_variable,0,0); }
and could i PQclear(pgresult_varible) while cstring_varible is in use.

thnx

Re: libpq-fe: PQgetvalue() ?

From
Christoph Haller
Date:
AFAIK it does allocate memory.
You cannot PQclear(pgresult_varible) while cstring_varible is in use.
You do not need to free cstring_variable, PQclear(pgresult_varible) will do.
I personally prefer to allocate local memory, "strcpy" PQgetvalue,
and then PQclear. But that's a matter of taste, I suppose.

Regards, Christoph


sad wrote:

> hi
>
> does PQgetvalue() allocate memory rof its result, it returns ?
> the answer will help me in problem:
> should i free some cstring_variable if
> { cstring_variable=PQgetvalue(pgresult_variable,0,0); }
> and could i PQclear(pgresult_varible) while cstring_varible is in use.
>
> thnx
>

Re: libpq-fe: PQgetvalue() ?

From
Tom Lane
Date:
Christoph Haller <ch@rodos.fzk.de> writes:
> You cannot PQclear(pgresult_varible) while cstring_varible is in use.
> You do not need to free cstring_variable, PQclear(pgresult_varible) will do.
> I personally prefer to allocate local memory, "strcpy" PQgetvalue,
> and then PQclear. But that's a matter of taste, I suppose.

That is surely overkill.

PQgetvalue doesn't allocate new memory for its result.  The docs are
reasonably clear, I thought:
    The pointer returned by PQgetvalue points to storage that is part    of the PGresult structure. One should not
modifythe data it points    to, and one must explicitly copy the data into other storage if it    is to be used past
thelifetime of the PGresult structure itself.
 
        regards, tom lane

Re: libpq-fe: PQgetvalue() ?

From
ljb
Date:
sad@bankir.ru wrote:
> hi
>
> does PQgetvalue() allocate memory rof its result, it returns ?
> the answer will help me in problem:
> should i free some cstring_variable if
> { cstring_variable=PQgetvalue(pgresult_variable,0,0); }
> and could i PQclear(pgresult_varible) while cstring_varible is in use.

From the documentation:   The pointer returned by PQgetvalue points to storage that is part of the PGresult structure.
Oneshould not modify the data it points to, and one must explicitly copy the data into other storage if it is to be
usedpast the lifetime of the PGresult structure itself.
 

So no, you must not free your copy of the pointer returned by PQgetvalue,
and no, once you PQclear the result your pointer is not valid. You should