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In developer's FAQ, update list API, from Tom Lane.

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Bruce Momjian
2007-05-05 10:21:13 +00:00
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doc/FAQ_DEV
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Developer's Frequently Asked Questions (FAQ) for PostgreSQL Developer's Frequently Asked Questions (FAQ) for PostgreSQL
Last updated: Sat May 5 00:09:15 EDT 2007 Last updated: Sat May 5 06:20:41 EDT 2007
Current maintainer: Bruce Momjian (bruce@momjian.us) Current maintainer: Bruce Momjian (bruce@momjian.us)
@ -698,20 +698,21 @@ typedef struct nameData
Here are some of the List manipulation commands: Here are some of the List manipulation commands:
lfirst(i), lfirst_int(i), lfirst_oid(i) lfirst(i), lfirst_int(i), lfirst_oid(i)
return the data (a point, integer and OID respectively) at list return the data (a pointer, integer or OID respectively) of
element i. list cell i.
lnext(i) lnext(i)
return the next list element after i. return the next list cell after i.
foreach(i, list) foreach(i, list)
loop through list, assigning each list element to i. It is loop through list, assigning each list cell to i. It is
important to note that i is a List *, not the data in the List important to note that i is a ListCell *, not the data in the
element. You need to use lfirst(i) to get at the data. Here is List element. You need to use lfirst(i) to get at the data.
a typical code snippet that loops through a List containing Var Here is a typical code snippet that loops through a List
*'s and processes each one: containing Var *'s and processes each one:
List *list;
List *list;
ListCell *i; ListCell *i;
foreach(i, list) foreach(i, list)
@ -726,20 +727,20 @@ typedef struct nameData
if list is NIL. if list is NIL.
lappend(list, node) lappend(list, node)
add node to the end of list. This is more expensive that lcons. add node to the end of list.
nconc(list1, list2) list_concat(list1, list2)
Concat list2 on to the end of list1. Concatenate list2 on to the end of list1.
length(list) list_length(list)
return the length of the list. return the length of the list.
nth(i, list) list_nth(list, i)
return the i'th element in list. return the i'th element in list, counting from zero.
lconsi, ... lcons_int, ...
There are integer versions of these: lconsi, lappendi, etc. There are integer versions of these: lcons_int, lappend_int,
Also versions for OID lists: lconso, lappendo, etc. etc. Also versions for OID lists: lcons_oid, lappend_oid, etc.
You can print nodes easily inside gdb. First, to disable output You can print nodes easily inside gdb. First, to disable output
truncation when you use the gdb print command: truncation when you use the gdb print command:
@ -758,7 +759,7 @@ typedef struct nameData
2.4) I just added a field to a structure. What else should I do? 2.4) I just added a field to a structure. What else should I do?
The structures passing around from the parser, rewrite, optimizer, and The structures passed around in the parser, rewriter, optimizer, and
executor require quite a bit of support. Most structures have support executor require quite a bit of support. Most structures have support
routines in src/backend/nodes used to create, copy, read, and output routines in src/backend/nodes used to create, copy, read, and output
those structures (in particular, the files copyfuncs.c and those structures (in particular, the files copyfuncs.c and

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<H1>Developer's Frequently Asked Questions (FAQ) for <H1>Developer's Frequently Asked Questions (FAQ) for
PostgreSQL</H1> PostgreSQL</H1>
<P>Last updated: Sat May 5 00:09:15 EDT 2007</P> <P>Last updated: Sat May 5 06:20:41 EDT 2007</P>
<P>Current maintainer: Bruce Momjian (<A href= <P>Current maintainer: Bruce Momjian (<A href=
"mailto:bruce@momjian.us">bruce@momjian.us</A>)<BR> "mailto:bruce@momjian.us">bruce@momjian.us</A>)<BR>
@ -863,24 +863,25 @@
<DL> <DL>
<DT>lfirst(i), lfirst_int(i), lfirst_oid(i)</DT> <DT>lfirst(i), lfirst_int(i), lfirst_oid(i)</DT>
<DD>return the data (a point, integer and OID respectively) at <DD>return the data (a pointer, integer or OID respectively) of
list element <I>i.</I></DD> list cell <I>i.</I></DD>
<DT>lnext(i)</DT> <DT>lnext(i)</DT>
<DD>return the next list element after <I>i.</I></DD> <DD>return the next list cell after <I>i.</I></DD>
<DT>foreach(i, list)</DT> <DT>foreach(i, list)</DT>
<DD> <DD>
loop through <I>list,</I> assigning each list element to loop through <I>list,</I> assigning each list cell to
<I>i.</I> It is important to note that <I>i</I> is a List *, <I>i.</I> It is important to note that <I>i</I> is a ListCell *,
not the data in the <I>List</I> element. You need to use not the data in the <I>List</I> element. You need to use
<I>lfirst(i)</I> to get at the data. Here is a typical code <I>lfirst(i)</I> to get at the data. Here is a typical code
snippet that loops through a List containing <I>Var *'s</I> snippet that loops through a List containing <I>Var *'s</I>
and processes each one: and processes each one:
<PRE> <PRE>
<CODE> List *list; <CODE>
List *list;
ListCell *i; ListCell *i;
foreach(i, list) foreach(i, list)
@ -900,26 +901,26 @@
<DT>lappend(list, node)</DT> <DT>lappend(list, node)</DT>
<DD>add <I>node</I> to the end of <I>list.</I> This is more <DD>add <I>node</I> to the end of <I>list.</I></DD>
expensive that lcons.</DD>
<DT>nconc(list1, list2)</DT> <DT>list_concat(list1, list2)</DT>
<DD>Concat <I>list2</I> on to the end of <I>list1.</I></DD> <DD>Concatenate <I>list2</I> on to the end of <I>list1.</I></DD>
<DT>length(list)</DT> <DT>list_length(list)</DT>
<DD>return the length of the <I>list.</I></DD> <DD>return the length of the <I>list.</I></DD>
<DT>nth(i, list)</DT> <DT>list_nth(list, i)</DT>
<DD>return the <I>i</I>'th element in <I>list.</I></DD> <DD>return the <I>i</I>'th element in <I>list,</I>
counting from zero.</DD>
<DT>lconsi, ...</DT> <DT>lcons_int, ...</DT>
<DD>There are integer versions of these: <I>lconsi, <DD>There are integer versions of these: <I>lcons_int,
lappendi</I>, etc. Also versions for OID lists: <I>lconso, lappend_int</I>, etc. Also versions for OID lists: <I>lcons_oid,
lappendo</I>, etc.</DD> lappend_oid</I>, etc.</DD>
</DL> </DL>
</BLOCKQUOTE> </BLOCKQUOTE>
You can print nodes easily inside <I>gdb.</I> First, to disable You can print nodes easily inside <I>gdb.</I> First, to disable
@ -944,7 +945,7 @@
<H3 id="item2.4">2.4) I just added a field to a structure. <H3 id="item2.4">2.4) I just added a field to a structure.
What else should I do?</H3> What else should I do?</H3>
<P>The structures passing around from the parser, rewrite, <P>The structures passed around in the parser, rewriter,
optimizer, and executor require quite a bit of support. Most optimizer, and executor require quite a bit of support. Most
structures have support routines in <I>src/backend/nodes</I> used structures have support routines in <I>src/backend/nodes</I> used
to create, copy, read, and output those structures (in particular, to create, copy, read, and output those structures (in particular,