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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>34.12. Miscellaneous Functions</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-control.html" title="34.11. Control Functions" /><link rel="next" href="libpq-notice-processing.html" title="34.13. Notice Processing" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">34.12. Miscellaneous Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="libpq-control.html" title="34.11. Control Functions">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 class="application">libpq</span> — C Library</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="libpq-notice-processing.html" title="34.13. Notice Processing">Next</a></td></tr></table><hr /></div><div class="sect1" id="LIBPQ-MISC"><div class="titlepage"><div><div><h2 class="title" style="clear: both">34.12. Miscellaneous Functions <a href="#LIBPQ-MISC" class="id_link">#</a></h2></div></div></div><p>
As always, there are some functions that just don't fit anywhere.
</p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQFREEMEM"><span class="term"><code class="function">PQfreemem</code><a id="id-1.7.3.19.3.1.1.2" class="indexterm"></a></span> <a href="#LIBPQ-PQFREEMEM" class="id_link">#</a></dt><dd><p>
Frees memory allocated by <span class="application">libpq</span>.
</p><pre class="synopsis">
void PQfreemem(void *ptr);
</pre><p>
</p><p>
Frees memory allocated by <span class="application">libpq</span>, particularly
<a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPEBYTEACONN"><code class="function">PQescapeByteaConn</code></a>,
<a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPEBYTEA"><code class="function">PQescapeBytea</code></a>,
<a class="xref" href="libpq-exec.html#LIBPQ-PQUNESCAPEBYTEA"><code class="function">PQunescapeBytea</code></a>,
and <code class="function">PQnotifies</code>.
It is particularly important that this function, rather than
<code class="function">free()</code>, be used on Microsoft Windows. This is because
allocating memory in a DLL and releasing it in the application works
only if multithreaded/single-threaded, release/debug, and static/dynamic
flags are the same for the DLL and the application. On non-Microsoft
Windows platforms, this function is the same as the standard library
function <code class="function">free()</code>.
</p></dd><dt id="LIBPQ-PQCONNINFOFREE"><span class="term"><code class="function">PQconninfoFree</code><a id="id-1.7.3.19.3.2.1.2" class="indexterm"></a></span> <a href="#LIBPQ-PQCONNINFOFREE" class="id_link">#</a></dt><dd><p>
Frees the data structures allocated by
<a class="xref" href="libpq-connect.html#LIBPQ-PQCONNDEFAULTS"><code class="function">PQconndefaults</code></a> or <a class="xref" href="libpq-connect.html#LIBPQ-PQCONNINFOPARSE"><code class="function">PQconninfoParse</code></a>.
</p><pre class="synopsis">
void PQconninfoFree(PQconninfoOption *connOptions);
</pre><p>
If the argument is a <code class="symbol">NULL</code> pointer, no operation is
performed.
</p><p>
A simple <a class="xref" href="libpq-misc.html#LIBPQ-PQFREEMEM"><code class="function">PQfreemem</code></a> will not do for this, since
the array contains references to subsidiary strings.
</p></dd><dt id="LIBPQ-PQENCRYPTPASSWORDCONN"><span class="term"><code class="function">PQencryptPasswordConn</code><a id="id-1.7.3.19.3.3.1.2" class="indexterm"></a></span> <a href="#LIBPQ-PQENCRYPTPASSWORDCONN" class="id_link">#</a></dt><dd><p>
Prepares the encrypted form of a <span class="productname">PostgreSQL</span> password.
</p><pre class="synopsis">
char *PQencryptPasswordConn(PGconn *conn, const char *passwd, const char *user, const char *algorithm);
</pre><p>
This function is intended to be used by client applications that
wish to send commands like <code class="literal">ALTER USER joe PASSWORD
'pwd'</code>. It is good practice not to send the original cleartext
password in such a command, because it might be exposed in command
logs, activity displays, and so on. Instead, use this function to
convert the password to encrypted form before it is sent.
</p><p>
The <em class="parameter"><code>passwd</code></em> and <em class="parameter"><code>user</code></em> arguments
are the cleartext password, and the SQL name of the user it is for.
<em class="parameter"><code>algorithm</code></em> specifies the encryption algorithm
to use to encrypt the password. Currently supported algorithms are
<code class="literal">md5</code> and <code class="literal">scram-sha-256</code> (<code class="literal">on</code> and
<code class="literal">off</code> are also accepted as aliases for <code class="literal">md5</code>, for
compatibility with older server versions). Note that support for
<code class="literal">scram-sha-256</code> was introduced in <span class="productname">PostgreSQL</span>
version 10, and will not work correctly with older server versions. If
<em class="parameter"><code>algorithm</code></em> is <code class="symbol">NULL</code>, this function will query
the server for the current value of the
<a class="xref" href="runtime-config-connection.html#GUC-PASSWORD-ENCRYPTION">password_encryption</a> setting. That can block, and
will fail if the current transaction is aborted, or if the connection
is busy executing another query. If you wish to use the default
algorithm for the server but want to avoid blocking, query
<code class="varname">password_encryption</code> yourself before calling
<a class="xref" href="libpq-misc.html#LIBPQ-PQENCRYPTPASSWORDCONN"><code class="function">PQencryptPasswordConn</code></a>, and pass that value as the
<em class="parameter"><code>algorithm</code></em>.
</p><p>
The return value is a string allocated by <code class="function">malloc</code>.
The caller can assume the string doesn't contain any special characters
that would require escaping. Use <a class="xref" href="libpq-misc.html#LIBPQ-PQFREEMEM"><code class="function">PQfreemem</code></a> to free the
result when done with it. On error, returns <code class="symbol">NULL</code>, and
a suitable message is stored in the connection object.
</p></dd><dt id="LIBPQ-PQENCRYPTPASSWORD"><span class="term"><code class="function">PQencryptPassword</code><a id="id-1.7.3.19.3.4.1.2" class="indexterm"></a></span> <a href="#LIBPQ-PQENCRYPTPASSWORD" class="id_link">#</a></dt><dd><p>
Prepares the md5-encrypted form of a <span class="productname">PostgreSQL</span> password.
</p><pre class="synopsis">
char *PQencryptPassword(const char *passwd, const char *user);
</pre><p>
<a class="xref" href="libpq-misc.html#LIBPQ-PQENCRYPTPASSWORD"><code class="function">PQencryptPassword</code></a> is an older, deprecated version of
<a class="xref" href="libpq-misc.html#LIBPQ-PQENCRYPTPASSWORDCONN"><code class="function">PQencryptPasswordConn</code></a>. The difference is that
<a class="xref" href="libpq-misc.html#LIBPQ-PQENCRYPTPASSWORD"><code class="function">PQencryptPassword</code></a> does not
require a connection object, and <code class="literal">md5</code> is always used as the
encryption algorithm.
</p></dd><dt id="LIBPQ-PQMAKEEMPTYPGRESULT"><span class="term"><code class="function">PQmakeEmptyPGresult</code><a id="id-1.7.3.19.3.5.1.2" class="indexterm"></a></span> <a href="#LIBPQ-PQMAKEEMPTYPGRESULT" class="id_link">#</a></dt><dd><p>
Constructs an empty <code class="structname">PGresult</code> object with the given status.
</p><pre class="synopsis">
PGresult *PQmakeEmptyPGresult(PGconn *conn, ExecStatusType status);
</pre><p>
</p><p>
This is <span class="application">libpq</span>'s internal function to allocate and
initialize an empty <code class="structname">PGresult</code> object. This
function returns <code class="symbol">NULL</code> if memory could not be allocated. It is
exported because some applications find it useful to generate result
objects (particularly objects with error status) themselves. If
<em class="parameter"><code>conn</code></em> is not null and <em class="parameter"><code>status</code></em>
indicates an error, the current error message of the specified
connection is copied into the <code class="structname">PGresult</code>.
Also, if <em class="parameter"><code>conn</code></em> is not null, any event procedures
registered in the connection are copied into the
<code class="structname">PGresult</code>. (They do not get
<code class="literal">PGEVT_RESULTCREATE</code> calls, but see
<a class="xref" href="libpq-misc.html#LIBPQ-PQFIRERESULTCREATEEVENTS"><code class="function">PQfireResultCreateEvents</code></a>.)
Note that <a class="xref" href="libpq-exec.html#LIBPQ-PQCLEAR"><code class="function">PQclear</code></a> should eventually be called
on the object, just as with a <code class="structname">PGresult</code>
returned by <span class="application">libpq</span> itself.
</p></dd><dt id="LIBPQ-PQFIRERESULTCREATEEVENTS"><span class="term"><code class="function">PQfireResultCreateEvents</code><a id="id-1.7.3.19.3.6.1.2" class="indexterm"></a></span> <a href="#LIBPQ-PQFIRERESULTCREATEEVENTS" class="id_link">#</a></dt><dd><p>
Fires a <code class="literal">PGEVT_RESULTCREATE</code> event (see <a class="xref" href="libpq-events.html" title="34.14. Event System">Section 34.14</a>) for each event procedure registered in the
<code class="structname">PGresult</code> object. Returns non-zero for success,
zero if any event procedure fails.
</p><pre class="synopsis">
int PQfireResultCreateEvents(PGconn *conn, PGresult *res);
</pre><p>
</p><p>
The <code class="literal">conn</code> argument is passed through to event procedures
but not used directly. It can be <code class="symbol">NULL</code> if the event
procedures won't use it.
</p><p>
Event procedures that have already received a
<code class="literal">PGEVT_RESULTCREATE</code> or <code class="literal">PGEVT_RESULTCOPY</code> event
for this object are not fired again.
</p><p>
The main reason that this function is separate from
<a class="xref" href="libpq-misc.html#LIBPQ-PQMAKEEMPTYPGRESULT"><code class="function">PQmakeEmptyPGresult</code></a> is that it is often appropriate
to create a <code class="structname">PGresult</code> and fill it with data
before invoking the event procedures.
</p></dd><dt id="LIBPQ-PQCOPYRESULT"><span class="term"><code class="function">PQcopyResult</code><a id="id-1.7.3.19.3.7.1.2" class="indexterm"></a></span> <a href="#LIBPQ-PQCOPYRESULT" class="id_link">#</a></dt><dd><p>
Makes a copy of a <code class="structname">PGresult</code> object. The copy is
not linked to the source result in any way and
<a class="xref" href="libpq-exec.html#LIBPQ-PQCLEAR"><code class="function">PQclear</code></a> must be called when the copy is no longer
needed. If the function fails, <code class="symbol">NULL</code> is returned.
</p><pre class="synopsis">
PGresult *PQcopyResult(const PGresult *src, int flags);
</pre><p>
</p><p>
This is not intended to make an exact copy. The returned result is
always put into <code class="literal">PGRES_TUPLES_OK</code> status, and does not
copy any error message in the source. (It does copy the command status
string, however.) The <em class="parameter"><code>flags</code></em> argument determines
what else is copied. It is a bitwise OR of several flags.
<code class="literal">PG_COPYRES_ATTRS</code> specifies copying the source
result's attributes (column definitions).
<code class="literal">PG_COPYRES_TUPLES</code> specifies copying the source
result's tuples. (This implies copying the attributes, too.)
<code class="literal">PG_COPYRES_NOTICEHOOKS</code> specifies
copying the source result's notify hooks.
<code class="literal">PG_COPYRES_EVENTS</code> specifies copying the source
result's events. (But any instance data associated with the source
is not copied.)
The event procedures receive <code class="literal">PGEVT_RESULTCOPY</code> events.
</p></dd><dt id="LIBPQ-PQSETRESULTATTRS"><span class="term"><code class="function">PQsetResultAttrs</code><a id="id-1.7.3.19.3.8.1.2" class="indexterm"></a></span> <a href="#LIBPQ-PQSETRESULTATTRS" class="id_link">#</a></dt><dd><p>
Sets the attributes of a <code class="structname">PGresult</code> object.
</p><pre class="synopsis">
int PQsetResultAttrs(PGresult *res, int numAttributes, PGresAttDesc *attDescs);
</pre><p>
</p><p>
The provided <em class="parameter"><code>attDescs</code></em> are copied into the result.
If the <em class="parameter"><code>attDescs</code></em> pointer is <code class="symbol">NULL</code> or
<em class="parameter"><code>numAttributes</code></em> is less than one, the request is
ignored and the function succeeds. If <em class="parameter"><code>res</code></em>
already contains attributes, the function will fail. If the function
fails, the return value is zero. If the function succeeds, the return
value is non-zero.
</p></dd><dt id="LIBPQ-PQSETVALUE"><span class="term"><code class="function">PQsetvalue</code><a id="id-1.7.3.19.3.9.1.2" class="indexterm"></a></span> <a href="#LIBPQ-PQSETVALUE" class="id_link">#</a></dt><dd><p>
Sets a tuple field value of a <code class="structname">PGresult</code> object.
</p><pre class="synopsis">
int PQsetvalue(PGresult *res, int tup_num, int field_num, char *value, int len);
</pre><p>
</p><p>
The function will automatically grow the result's internal tuples array
as needed. However, the <em class="parameter"><code>tup_num</code></em> argument must be
less than or equal to <a class="xref" href="libpq-exec.html#LIBPQ-PQNTUPLES"><code class="function">PQntuples</code></a>, meaning this
function can only grow the tuples array one tuple at a time. But any
field of any existing tuple can be modified in any order. If a value at
<em class="parameter"><code>field_num</code></em> already exists, it will be overwritten.
If <em class="parameter"><code>len</code></em> is -1 or
<em class="parameter"><code>value</code></em> is <code class="symbol">NULL</code>, the field value
will be set to an SQL null value. The
<em class="parameter"><code>value</code></em> is copied into the result's private storage,
thus is no longer needed after the function
returns. If the function fails, the return value is zero. If the
function succeeds, the return value is non-zero.
</p></dd><dt id="LIBPQ-PQRESULTALLOC"><span class="term"><code class="function">PQresultAlloc</code><a id="id-1.7.3.19.3.10.1.2" class="indexterm"></a></span> <a href="#LIBPQ-PQRESULTALLOC" class="id_link">#</a></dt><dd><p>
Allocate subsidiary storage for a <code class="structname">PGresult</code> object.
</p><pre class="synopsis">
void *PQresultAlloc(PGresult *res, size_t nBytes);
</pre><p>
</p><p>
Any memory allocated with this function will be freed when
<em class="parameter"><code>res</code></em> is cleared. If the function fails,
the return value is <code class="symbol">NULL</code>. The result is
guaranteed to be adequately aligned for any type of data,
just as for <code class="function">malloc</code>.
</p></dd><dt id="LIBPQ-PQRESULTMEMORYSIZE"><span class="term"><code class="function">PQresultMemorySize</code><a id="id-1.7.3.19.3.11.1.2" class="indexterm"></a></span> <a href="#LIBPQ-PQRESULTMEMORYSIZE" class="id_link">#</a></dt><dd><p>
Retrieves the number of bytes allocated for
a <code class="structname">PGresult</code> object.
</p><pre class="synopsis">
size_t PQresultMemorySize(const PGresult *res);
</pre><p>
</p><p>
This value is the sum of all <code class="function">malloc</code> requests
associated with the <code class="structname">PGresult</code> object, that is,
all the space that will be freed by <a class="xref" href="libpq-exec.html#LIBPQ-PQCLEAR"><code class="function">PQclear</code></a>.
This information can be useful for managing memory consumption.
</p></dd><dt id="LIBPQ-PQLIBVERSION"><span class="term"><code class="function">PQlibVersion</code><a id="id-1.7.3.19.3.12.1.2" class="indexterm"></a></span> <a href="#LIBPQ-PQLIBVERSION" class="id_link">#</a></dt><dd><p>
Return the version of <span class="productname">libpq</span> that is being used.
</p><pre class="synopsis">
int PQlibVersion(void);
</pre><p>
</p><p>
The result of this function can be used to determine, at
run time, whether specific functionality is available in the currently
loaded version of libpq. The function can be used, for example,
to determine which connection options are available in
<a class="xref" href="libpq-connect.html#LIBPQ-PQCONNECTDB"><code class="function">PQconnectdb</code></a>.
</p><p>
The result is formed by multiplying the library's major version
number by 10000 and adding the minor version number. For example,
version 10.1 will be returned as 100001, and version 11.0 will be
returned as 110000.
</p><p>
Prior to major version 10, <span class="productname">PostgreSQL</span> used
three-part version numbers in which the first two parts together
represented the major version. For those
versions, <a class="xref" href="libpq-misc.html#LIBPQ-PQLIBVERSION"><code class="function">PQlibVersion</code></a> uses two digits for each
part; for example version 9.1.5 will be returned as 90105, and
version 9.2.0 will be returned as 90200.
</p><p>
Therefore, for purposes of determining feature compatibility,
applications should divide the result of <a class="xref" href="libpq-misc.html#LIBPQ-PQLIBVERSION"><code class="function">PQlibVersion</code></a>
by 100 not 10000 to determine a logical major version number.
In all release series, only the last two digits differ between
minor releases (bug-fix releases).
</p><div class="note"><h3 class="title">Note</h3><p>
This function appeared in <span class="productname">PostgreSQL</span> version 9.1, so
it cannot be used to detect required functionality in earlier
versions, since calling it will create a link dependency
on version 9.1 or later.
</p></div></dd></dl></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="libpq-control.html" title="34.11. Control Functions">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="libpq.html" title="Chapter 34. libpq — C Library">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="libpq-notice-processing.html" title="34.13. Notice Processing">Next</a></td></tr><tr><td width="40%" align="left" valign="top">34.11. Control Functions </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 34.13. Notice Processing</td></tr></table></div></body></html>