sending data with COPY SQL command, libpq and structure of SELECT resulting buffer

I sent this message to INTERFACES, but there is no answer, maybe on
ADMIN list somebody knows something about it...
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 From the docs i understood, that with COPY SQL command we should use
for synchr. sending:
PQexec
PQResultstatus returns PGRES_COPY_OUT
PQputCopyData
PQputCopyEnd
PQResultstatus returns PGRES_COMMAND_OK

How should look the structure of buffer in
int PQputCopyData(PGconn *conn,const char *buffer,int nbytes);
id for me clear (it should be the same like for example in text dumps of
tables done with pg_dump).

The question is:
Can I in function:
int PQputCopyData(PGconn *conn,const char *buffer,int nbytes);
use as a result buffer directly given by using PQexec for SELECT SQL
command ?
In other way:
Is the structure given as result of PQexec with SELECT SQL command
directly usable as buffer for PQputCopyData ?
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Brgds
Adam