The COPY command in PostgreSQL has options to read from or write to the network connection used by libpq++. Therefore, functions are necessary to access this network connection directly so applications may take full advantage of this capability.
PgDatabase::GetLine
reads a newline-terminated line of characters (transmitted by the
backend server) into a buffer
string
of size length.
int PgDatabase::GetLine(char* string, int length)
Like the Unix system routine
fgets()
,
this routine copies up to
length-1
characters into
string.
It is like
gets()
,
however, in that it converts the terminating newline into a zero byte.
PgDatabase::GetLine
returns EOF at end of file, 0 if the entire line has been read, and 1 if the
buffer is full but the terminating newline has not yet been read.
Notice that the application must check to see if a new line consists
of a backslash followed by a period (\.), which indicates
that the backend
server has finished sending the results of the
COPY.
Therefore, if the application ever expects to receive lines
that are more than
length-1
characters long, the application must be sure to check the return
value of PgDatabase::GetLine
very carefully.
PgDatabase::PutLine
Sends a null-terminated string
to the backend server.
void PgDatabase::PutLine(char* string)
The application must explicitly send the characters \. to indicate to the backend that it has finished sending its data.
PgDatabase::EndCopy
synchronizes with the backend.
int PgDatabase::EndCopy()
This function waits until the backend has
finished processing the COPY.
It should either be issued when the
last string has been sent to the backend using
PgDatabase::PutLine
or when the last string has been received from the backend using
PgDatabase::GetLine
.
It must be issued or the backend may get "out of sync" with
the frontend. Upon return from this function, the backend is ready to
receive the next command.
The return value is 0 on successful completion, nonzero otherwise.
As an example:
PgDatabase data; data.Exec("CREATE TABLE foo (a int4, b char(16), d double precision)"); data.Exec("COPY foo FROM STDIN"); data.PutLine("3\tHello World\t4.5\n"); data.PutLine("4\tGoodbye World\t7.11\n"); ... data.PutLine("\\.\n"); data.EndCopy();