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();