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Doc: modernize documentation for lo_create()/lo_creat().

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At this point lo_creat() is a legacy function with little if any
real use-case, so describing it first doesn't make much sense.
Describe lo_create() first, and then explain lo_creat() as a
backwards-compatibility alternative.

Discussion: https://postgr.es/m/164353261519.713.8748040527537500758@wrigleys.postgresql.org
This commit is contained in:
Tom Lane 2022-02-01 10:57:26 -05:00
parent 0526f2f4c3
commit a5a9d77b8b
1 changed files with 37 additions and 35 deletions
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72
doc/src/sgml/lobj.sgml
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@ -138,19 +138,50 @@
<title>Creating a Large Object</title>
<para>
<indexterm><primary>lo_creat</primary></indexterm>
<indexterm><primary>lo_create</primary></indexterm>
The function
<synopsis>
Oid lo_create(PGconn *conn, Oid lobjId);
</synopsis>
creates a new large object. The OID to be assigned can be
specified by <replaceable class="parameter">lobjId</replaceable>;
if so, failure occurs if that OID is already in use for some large
object. If <replaceable class="parameter">lobjId</replaceable>
is <symbol>InvalidOid</symbol> (zero) then <function>lo_create</function>
assigns an unused OID.
The return value is the OID that was assigned to the new large object,
or <symbol>InvalidOid</symbol> (zero) on failure.
</para>
<para>
An example:
<programlisting>
inv_oid = lo_create(conn, desired_oid);
</programlisting>
</para>
<para>
<indexterm><primary>lo_creat</primary></indexterm>
The older function
<synopsis>
Oid lo_creat(PGconn *conn, int mode);
</synopsis>
creates a new large object.
also creates a new large object, always assigning an unused OID.
The return value is the OID that was assigned to the new large object,
or <symbol>InvalidOid</symbol> (zero) on failure.
</para>
<replaceable class="parameter">mode</replaceable> is unused and
ignored as of <productname>PostgreSQL</productname> 8.1; however, for
backward compatibility with earlier releases it is best to
set it to <symbol>INV_READ</symbol>, <symbol>INV_WRITE</symbol>,
<para>
In <productname>PostgreSQL</productname> releases 8.1 and later,
the <replaceable class="parameter">mode</replaceable> is ignored,
so that <function>lo_creat</function> is exactly equivalent to
<function>lo_create</function> with a zero second argument.
However, there is little reason to use <function>lo_creat</function>
unless you need to work with servers older than 8.1.
To work with such an old server, you must
use <function>lo_creat</function> not <function>lo_create</function>,
and you must set <replaceable class="parameter">mode</replaceable> to
one of <symbol>INV_READ</symbol>, <symbol>INV_WRITE</symbol>,
or <symbol>INV_READ</symbol> <literal>|</literal> <symbol>INV_WRITE</symbol>.
(These symbolic constants are defined
in the header file <filename>libpq/libpq-fs.h</filename>.)
@ -160,35 +191,6 @@ Oid lo_creat(PGconn *conn, int mode);
An example:
<programlisting>
inv_oid = lo_creat(conn, INV_READ|INV_WRITE);
</programlisting>
</para>
<para>
<indexterm><primary>lo_create</primary></indexterm>
The function
<synopsis>
Oid lo_create(PGconn *conn, Oid lobjId);
</synopsis>
also creates a new large object. The OID to be assigned can be
specified by <replaceable class="parameter">lobjId</replaceable>;
if so, failure occurs if that OID is already in use for some large
object. If <replaceable class="parameter">lobjId</replaceable>
is <symbol>InvalidOid</symbol> (zero) then <function>lo_create</function> assigns an unused
OID (this is the same behavior as <function>lo_creat</function>).
The return value is the OID that was assigned to the new large object,
or <symbol>InvalidOid</symbol> (zero) on failure.
</para>
<para>
<function>lo_create</function> is new as of <productname>PostgreSQL</productname>
8.1; if this function is run against an older server version, it will
fail and return <symbol>InvalidOid</symbol>.
</para>
<para>
An example:
<programlisting>
inv_oid = lo_create(conn, desired_oid);
</programlisting>
</para>
</sect2>