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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>34.9. Functions Associated with the COPY Command</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="libpq-notify.html" title="34.8. Asynchronous Notification" /><link rel="next" href="libpq-control.html" title="34.10. Control Functions" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">34.9. Functions Associated with the <code xmlns="http://www.w3.org/1999/xhtml" class="command">COPY</code> Command</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="libpq-notify.html" title="34.8. Asynchronous Notification">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="libpq.html" title="Chapter 34. libpq - C Library">Up</a></td><th width="60%" align="center">Chapter 34. <span xmlns="http://www.w3.org/1999/xhtml" class="application">libpq</span> - C Library</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="libpq-control.html" title="34.10. Control Functions">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="LIBPQ-COPY"><div class="titlepage"><div><div><h2 class="title" style="clear: both">34.9. Functions Associated with the <code class="command">COPY</code> Command</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="libpq-copy.html#LIBPQ-COPY-SEND">34.9.1. Functions for Sending <code class="command">COPY</code> Data</a></span></dt><dt><span class="sect2"><a href="libpq-copy.html#LIBPQ-COPY-RECEIVE">34.9.2. Functions for Receiving <code class="command">COPY</code> Data</a></span></dt><dt><span class="sect2"><a href="libpq-copy.html#LIBPQ-COPY-DEPRECATED">34.9.3. Obsolete Functions for <code class="command">COPY</code></a></span></dt></dl></div><a id="id-1.7.3.16.2" class="indexterm"></a><p>
The <code class="command">COPY</code> command in
<span class="productname">PostgreSQL</span> has options to read from or write
to the network connection used by <span class="application">libpq</span>.
The functions described in this section allow applications to take
advantage of this capability by supplying or consuming copied data.
</p><p>
The overall process is that the application first issues the SQL
<code class="command">COPY</code> command via <code class="function">PQexec</code> or one
of the equivalent functions. The response to this (if there is no
error in the command) will be a <code class="structname">PGresult</code> object bearing
a status code of <code class="literal">PGRES_COPY_OUT</code> or
<code class="literal">PGRES_COPY_IN</code> (depending on the specified copy
direction). The application should then use the functions of this
section to receive or transmit data rows. When the data transfer is
complete, another <code class="structname">PGresult</code> object is returned to indicate
success or failure of the transfer. Its status will be
<code class="literal">PGRES_COMMAND_OK</code> for success or
<code class="literal">PGRES_FATAL_ERROR</code> if some problem was encountered.
At this point further SQL commands can be issued via
<code class="function">PQexec</code>. (It is not possible to execute other SQL
commands using the same connection while the <code class="command">COPY</code>
operation is in progress.)
</p><p>
If a <code class="command">COPY</code> command is issued via
<code class="function">PQexec</code> in a string that could contain additional
commands, the application must continue fetching results via
<code class="function">PQgetResult</code> after completing the <code class="command">COPY</code>
sequence. Only when <code class="function">PQgetResult</code> returns
<code class="symbol">NULL</code> is it certain that the <code class="function">PQexec</code>
command string is done and it is safe to issue more commands.
</p><p>
The functions of this section should be executed only after obtaining
a result status of <code class="literal">PGRES_COPY_OUT</code> or
<code class="literal">PGRES_COPY_IN</code> from <code class="function">PQexec</code> or
<code class="function">PQgetResult</code>.
</p><p>
A <code class="structname">PGresult</code> object bearing one of these status values
carries some additional data about the <code class="command">COPY</code> operation
that is starting. This additional data is available using functions
that are also used in connection with query results:
</p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQNFIELDS-1"><span class="term">
<code class="function">PQnfields</code>
<a id="id-1.7.3.16.7.3.1.1.2" class="indexterm"></a>
</span></dt><dd><p>
Returns the number of columns (fields) to be copied.
</p></dd><dt id="LIBPQ-PQBINARYTUPLES-1"><span class="term">
<code class="function">PQbinaryTuples</code>
<a id="id-1.7.3.16.7.3.2.1.2" class="indexterm"></a>
</span></dt><dd><p>
0 indicates the overall copy format is textual (rows separated by
newlines, columns separated by separator characters, etc). 1
indicates the overall copy format is binary. See <a class="xref" href="sql-copy.html" title="COPY"><span class="refentrytitle">COPY</span></a> for more information.
</p></dd><dt id="LIBPQ-PQFFORMAT-1"><span class="term">
<code class="function">PQfformat</code>
<a id="id-1.7.3.16.7.3.3.1.2" class="indexterm"></a>
</span></dt><dd><p>
Returns the format code (0 for text, 1 for binary) associated with
each column of the copy operation. The per-column format codes
will always be zero when the overall copy format is textual, but
the binary format can support both text and binary columns.
(However, as of the current implementation of <code class="command">COPY</code>,
only binary columns appear in a binary copy; so the per-column
formats always match the overall format at present.)
</p></dd></dl></div><p>
</p><div class="note"><h3 class="title">Note</h3><p>
These additional data values are only available when using protocol
3.0. When using protocol 2.0, all these functions will return 0.
</p></div><div class="sect2" id="LIBPQ-COPY-SEND"><div class="titlepage"><div><div><h3 class="title">34.9.1. Functions for Sending <code class="command">COPY</code> Data</h3></div></div></div><p>
These functions are used to send data during <code class="literal">COPY FROM
STDIN</code>. They will fail if called when the connection is not in
<code class="literal">COPY_IN</code> state.
</p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQPUTCOPYDATA"><span class="term">
<code class="function">PQputCopyData</code>
<a id="id-1.7.3.16.9.3.1.1.2" class="indexterm"></a>
</span></dt><dd><p>
Sends data to the server during <code class="literal">COPY_IN</code> state.
</p><pre class="synopsis">
int PQputCopyData(PGconn *conn,
const char *buffer,
int nbytes);
</pre><p>
</p><p>
Transmits the <code class="command">COPY</code> data in the specified
<em class="parameter"><code>buffer</code></em>, of length <em class="parameter"><code>nbytes</code></em>, to the server.
The result is 1 if the data was queued, zero if it was not queued
because of full buffers (this will only happen in nonblocking mode),
or -1 if an error occurred.
(Use <code class="function">PQerrorMessage</code> to retrieve details if
the return value is -1. If the value is zero, wait for write-ready
and try again.)
</p><p>
The application can divide the <code class="command">COPY</code> data stream
into buffer loads of any convenient size. Buffer-load boundaries
have no semantic significance when sending. The contents of the
data stream must match the data format expected by the
<code class="command">COPY</code> command; see <a class="xref" href="sql-copy.html" title="COPY"><span class="refentrytitle">COPY</span></a> for details.
</p></dd><dt id="LIBPQ-PQPUTCOPYEND"><span class="term">
<code class="function">PQputCopyEnd</code>
<a id="id-1.7.3.16.9.3.2.1.2" class="indexterm"></a>
</span></dt><dd><p>
Sends end-of-data indication to the server during <code class="literal">COPY_IN</code> state.
</p><pre class="synopsis">
int PQputCopyEnd(PGconn *conn,
const char *errormsg);
</pre><p>
</p><p>
Ends the <code class="literal">COPY_IN</code> operation successfully if
<em class="parameter"><code>errormsg</code></em> is <code class="symbol">NULL</code>. If
<em class="parameter"><code>errormsg</code></em> is not <code class="symbol">NULL</code> then the
<code class="command">COPY</code> is forced to fail, with the string pointed to by
<em class="parameter"><code>errormsg</code></em> used as the error message. (One should not
assume that this exact error message will come back from the server,
however, as the server might have already failed the
<code class="command">COPY</code> for its own reasons. Also note that the option
to force failure does not work when using pre-3.0-protocol
connections.)
</p><p>
The result is 1 if the termination message was sent; or in
nonblocking mode, this may only indicate that the termination
message was successfully queued. (In nonblocking mode, to be
certain that the data has been sent, you should next wait for
write-ready and call <code class="function">PQflush</code>, repeating until it
returns zero.) Zero indicates that the function could not queue
the termination message because of full buffers; this will only
happen in nonblocking mode. (In this case, wait for
write-ready and try the <code class="function">PQputCopyEnd</code> call
again.) If a hard error occurs, -1 is returned; you can use
<code class="function">PQerrorMessage</code> to retrieve details.
</p><p>
After successfully calling <code class="function">PQputCopyEnd</code>, call
<code class="function">PQgetResult</code> to obtain the final result status of the
<code class="command">COPY</code> command. One can wait for this result to be
available in the usual way. Then return to normal operation.
</p></dd></dl></div></div><div class="sect2" id="LIBPQ-COPY-RECEIVE"><div class="titlepage"><div><div><h3 class="title">34.9.2. Functions for Receiving <code class="command">COPY</code> Data</h3></div></div></div><p>
These functions are used to receive data during <code class="literal">COPY TO
STDOUT</code>. They will fail if called when the connection is not in
<code class="literal">COPY_OUT</code> state.
</p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQGETCOPYDATA"><span class="term">
<code class="function">PQgetCopyData</code>
<a id="id-1.7.3.16.10.3.1.1.2" class="indexterm"></a>
</span></dt><dd><p>
Receives data from the server during <code class="literal">COPY_OUT</code> state.
</p><pre class="synopsis">
int PQgetCopyData(PGconn *conn,
char **buffer,
int async);
</pre><p>
</p><p>
Attempts to obtain another row of data from the server during a
<code class="command">COPY</code>. Data is always returned one data row at
a time; if only a partial row is available, it is not returned.
Successful return of a data row involves allocating a chunk of
memory to hold the data. The <em class="parameter"><code>buffer</code></em> parameter must
be non-<code class="symbol">NULL</code>. <em class="parameter"><code>*buffer</code></em> is set to
point to the allocated memory, or to <code class="symbol">NULL</code> in cases
where no buffer is returned. A non-<code class="symbol">NULL</code> result
buffer should be freed using <code class="function">PQfreemem</code> when no longer
needed.
</p><p>
When a row is successfully returned, the return value is the number
of data bytes in the row (this will always be greater than zero).
The returned string is always null-terminated, though this is
probably only useful for textual <code class="command">COPY</code>. A result
of zero indicates that the <code class="command">COPY</code> is still in
progress, but no row is yet available (this is only possible when
<em class="parameter"><code>async</code></em> is true). A result of -1 indicates that the
<code class="command">COPY</code> is done. A result of -2 indicates that an
error occurred (consult <code class="function">PQerrorMessage</code> for the reason).
</p><p>
When <em class="parameter"><code>async</code></em> is true (not zero),
<code class="function">PQgetCopyData</code> will not block waiting for input; it
will return zero if the <code class="command">COPY</code> is still in progress
but no complete row is available. (In this case wait for read-ready
and then call <code class="function">PQconsumeInput</code> before calling
<code class="function">PQgetCopyData</code> again.) When <em class="parameter"><code>async</code></em> is
false (zero), <code class="function">PQgetCopyData</code> will block until data is
available or the operation completes.
</p><p>
After <code class="function">PQgetCopyData</code> returns -1, call
<code class="function">PQgetResult</code> to obtain the final result status of the
<code class="command">COPY</code> command. One can wait for this result to be
available in the usual way. Then return to normal operation.
</p></dd></dl></div></div><div class="sect2" id="LIBPQ-COPY-DEPRECATED"><div class="titlepage"><div><div><h3 class="title">34.9.3. Obsolete Functions for <code class="command">COPY</code></h3></div></div></div><p>
These functions represent older methods of handling <code class="command">COPY</code>.
Although they still work, they are deprecated due to poor error handling,
inconvenient methods of detecting end-of-data, and lack of support for binary
or nonblocking transfers.
</p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQGETLINE"><span class="term">
<code class="function">PQgetline</code>
<a id="id-1.7.3.16.11.3.1.1.2" class="indexterm"></a>
</span></dt><dd><p>
Reads a newline-terminated line of characters (transmitted
by the server) into a buffer string of size <em class="parameter"><code>length</code></em>.
</p><pre class="synopsis">
int PQgetline(PGconn *conn,
char *buffer,
int length);
</pre><p>
</p><p>
This function copies up to <em class="parameter"><code>length</code></em>-1 characters into
the buffer and converts the terminating newline into a zero byte.
<code class="function">PQgetline</code> returns <code class="symbol">EOF</code> at the
end of input, 0 if the entire line has been read, and 1 if the
buffer is full but the terminating newline has not yet been read.
</p><p>
Note that the application must check to see if a new line consists
of the two characters <code class="literal">\.</code>, which indicates
that the server has finished sending the results of the
<code class="command">COPY</code> command. If the application might receive
lines that are more than <em class="parameter"><code>length</code></em>-1 characters long,
care is needed to be sure it recognizes the <code class="literal">\.</code>
line correctly (and does not, for example, mistake the end of a
long data line for a terminator line).
</p></dd><dt id="LIBPQ-PQGETLINEASYNC"><span class="term">
<code class="function">PQgetlineAsync</code>
<a id="id-1.7.3.16.11.3.2.1.2" class="indexterm"></a>
</span></dt><dd><p>
Reads a row of <code class="command">COPY</code> data (transmitted by the
server) into a buffer without blocking.
</p><pre class="synopsis">
int PQgetlineAsync(PGconn *conn,
char *buffer,
int bufsize);
</pre><p>
</p><p>
This function is similar to <code class="function">PQgetline</code>, but it can be used
by applications
that must read <code class="command">COPY</code> data asynchronously, that is, without blocking.
Having issued the <code class="command">COPY</code> command and gotten a <code class="literal">PGRES_COPY_OUT</code>
response, the
application should call <code class="function">PQconsumeInput</code> and
<code class="function">PQgetlineAsync</code> until the
end-of-data signal is detected.
</p><p>
Unlike <code class="function">PQgetline</code>, this function takes
responsibility for detecting end-of-data.
</p><p>
On each call, <code class="function">PQgetlineAsync</code> will return data if a
complete data row is available in <span class="application">libpq</span>'s input buffer.
Otherwise, no data is returned until the rest of the row arrives.
The function returns -1 if the end-of-copy-data marker has been recognized,
or 0 if no data is available, or a positive number giving the number of
bytes of data returned. If -1 is returned, the caller must next call
<code class="function">PQendcopy</code>, and then return to normal processing.
</p><p>
The data returned will not extend beyond a data-row boundary. If possible
a whole row will be returned at one time. But if the buffer offered by
the caller is too small to hold a row sent by the server, then a partial
data row will be returned. With textual data this can be detected by testing
whether the last returned byte is <code class="literal">\n</code> or not. (In a binary
<code class="command">COPY</code>, actual parsing of the <code class="command">COPY</code> data format will be needed to make the
equivalent determination.)
The returned string is not null-terminated. (If you want to add a
terminating null, be sure to pass a <em class="parameter"><code>bufsize</code></em> one smaller
than the room actually available.)
</p></dd><dt id="LIBPQ-PQPUTLINE"><span class="term">
<code class="function">PQputline</code>
<a id="id-1.7.3.16.11.3.3.1.2" class="indexterm"></a>
</span></dt><dd><p>
Sends a null-terminated string to the server. Returns 0 if
OK and <code class="symbol">EOF</code> if unable to send the string.
</p><pre class="synopsis">
int PQputline(PGconn *conn,
const char *string);
</pre><p>
</p><p>
The <code class="command">COPY</code> data stream sent by a series of calls
to <code class="function">PQputline</code> has the same format as that
returned by <code class="function">PQgetlineAsync</code>, except that
applications are not obliged to send exactly one data row per
<code class="function">PQputline</code> call; it is okay to send a partial
line or multiple lines per call.
</p><div class="note"><h3 class="title">Note</h3><p>
Before <span class="productname">PostgreSQL</span> protocol 3.0, it was necessary
for the application to explicitly send the two characters
<code class="literal">\.</code> as a final line to indicate to the server that it had
finished sending <code class="command">COPY</code> data. While this still works, it is deprecated and the
special meaning of <code class="literal">\.</code> can be expected to be removed in a
future release. It is sufficient to call <code class="function">PQendcopy</code> after
having sent the actual data.
</p></div></dd><dt id="LIBPQ-PQPUTNBYTES"><span class="term">
<code class="function">PQputnbytes</code>
<a id="id-1.7.3.16.11.3.4.1.2" class="indexterm"></a>
</span></dt><dd><p>
Sends a non-null-terminated string to the server. Returns
0 if OK and <code class="symbol">EOF</code> if unable to send the string.
</p><pre class="synopsis">
int PQputnbytes(PGconn *conn,
const char *buffer,
int nbytes);
</pre><p>
</p><p>
This is exactly like <code class="function">PQputline</code>, except that the data
buffer need not be null-terminated since the number of bytes to send is
specified directly. Use this procedure when sending binary data.
</p></dd><dt id="LIBPQ-PQENDCOPY"><span class="term">
<code class="function">PQendcopy</code>
<a id="id-1.7.3.16.11.3.5.1.2" class="indexterm"></a>
</span></dt><dd><p>
Synchronizes with the server.
</p><pre class="synopsis">
int PQendcopy(PGconn *conn);
</pre><p>
This function waits until the server has finished the copying.
It should either be issued when the last string has been sent
to the server using <code class="function">PQputline</code> or when the
last string has been received from the server using
<code class="function">PGgetline</code>. It must be issued or the server
will get <span class="quote">“<span class="quote">out of sync</span>”</span> with the client. Upon return
from this function, the server is ready to receive the next SQL
command. The return value is 0 on successful completion,
nonzero otherwise. (Use <code class="function">PQerrorMessage</code> to
retrieve details if the return value is nonzero.)
</p><p>
When using <code class="function">PQgetResult</code>, the application should
respond to a <code class="literal">PGRES_COPY_OUT</code> result by executing
<code class="function">PQgetline</code> repeatedly, followed by
<code class="function">PQendcopy</code> after the terminator line is seen.
It should then return to the <code class="function">PQgetResult</code> loop
until <code class="function">PQgetResult</code> returns a null pointer.
Similarly a <code class="literal">PGRES_COPY_IN</code> result is processed
by a series of <code class="function">PQputline</code> calls followed by
<code class="function">PQendcopy</code>, then return to the
<code class="function">PQgetResult</code> loop. This arrangement will
ensure that a <code class="command">COPY</code> command embedded in a series
of <acronym class="acronym">SQL</acronym> commands will be executed correctly.
</p><p>
Older applications are likely to submit a <code class="command">COPY</code>
via <code class="function">PQexec</code> and assume that the transaction
is done after <code class="function">PQendcopy</code>. This will work
correctly only if the <code class="command">COPY</code> is the only
<acronym class="acronym">SQL</acronym> command in the command string.
</p></dd></dl></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="libpq-notify.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="libpq.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="libpq-control.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">34.8. Asynchronous Notification </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 34.10. Control Functions</td></tr></table></div></body></html>
