Functions Associated with the COPY Command

PostgreSQL 7.2 Documentation
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# 3.7. Functions Associated with the COPY Command

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();

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