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<TITLE>CLHS: Section 22.3</TITLE>
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<H1><A REV=MADE HREF="http://www.lispworks.com/"><IMG WIDTH=80 HEIGHT=65 ALT="[LISPWORKS]" SRC="../Graphics/LWSmall.gif" ALIGN=Bottom></A><A REL=TOP HREF="../Front/index.htm"><IMG WIDTH=237 HEIGHT=65 ALT="[Common Lisp HyperSpec (TM)]" SRC="../Graphics/CLHS_Sm.gif" ALIGN=Bottom></A> <A REL=PREV HREF="22_bc.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="22_.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="22_ca.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>
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22.3 Formatted Output</H2> <P>
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<P>
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<A REL=DEFINITION HREF="f_format.htm#format"><B>format</B></A> is useful for producing nicely formatted text, producing good-looking messages, and so on. <A REL=DEFINITION HREF="f_format.htm#format"><B>format</B></A> can generate and return a <A REL=DEFINITION HREF="26_glo_s.htm#string"><I>string</I></A> or output to <I>destination</I>. <P>
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The <I>control-string</I> argument to <A REL=DEFINITION HREF="f_format.htm#format"><B>format</B></A> is actually a <A REL=DEFINITION HREF="26_glo_f.htm#format_control"><I>format control</I></A>. That is, it can be either a <A REL=DEFINITION HREF="26_glo_f.htm#format_string"><I>format string</I></A> or a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A>, for example a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> returned by the <A REL=DEFINITION HREF="m_format.htm#formatter"><B>formatter</B></A> <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A>. <P>
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If it is a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A>, the <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> is called with the appropriate output stream as its first argument and the data arguments to <A REL=DEFINITION HREF="f_format.htm#format"><B>format</B></A> as its remaining arguments. The function should perform whatever output is necessary and return the unused tail of the arguments (if any). <P>
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The compilation process performed by <A REL=DEFINITION HREF="m_format.htm#formatter"><B>formatter</B></A> produces a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> that would do with its <A REL=DEFINITION HREF="26_glo_a.htm#argument"><I>arguments</I></A> as the <A REL=DEFINITION HREF="f_format.htm#format"><B>format</B></A> interpreter would do with those <A REL=DEFINITION HREF="26_glo_a.htm#argument"><I>arguments</I></A>. <P>
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The remainder of this section describes what happens if the <I>control-string</I> is a <A REL=DEFINITION HREF="26_glo_f.htm#format_string"><I>format string</I></A>. <P>
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<I>Control-string</I> is composed of simple text (<A REL=DEFINITION HREF="26_glo_c.htm#character"><I>characters</I></A>) and embedded directives. <P>
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<A REL=DEFINITION HREF="f_format.htm#format"><B>format</B></A> writes the simple text as is; each embedded directive specifies further text output that is to appear at the corresponding point within the simple text. Most directives use one or more elements of <I>args</I> to create their output. <P>
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A directive consists of a <A REL=DEFINITION HREF="26_glo_t.htm#tilde"><I>tilde</I></A>, optional prefix parameters separated by commas, optional <A REL=DEFINITION HREF="26_glo_c.htm#colon"><I>colon</I></A> and <A REL=DEFINITION HREF="26_glo_a.htm#at-sign"><I>at-sign</I></A> modifiers, and a single character indicating what kind of directive this is. There is no required ordering between the <A REL=DEFINITION HREF="26_glo_a.htm#at-sign"><I>at-sign</I></A> and <A REL=DEFINITION HREF="26_glo_c.htm#colon"><I>colon</I></A> modifier. The <A REL=DEFINITION HREF="26_glo_c.htm#case"><I>case</I></A> of the directive character is ignored. Prefix parameters are notated as signed (sign is optional) decimal numbers, or as a <A REL=DEFINITION HREF="26_glo_s.htm#single-quote"><I>single-quote</I></A> followed by a character. For example, <TT>~5,'0d</TT> can be used to print an <A REL=DEFINITION HREF="26_glo_i.htm#integer"><I>integer</I></A> in decimal radix in five columns with leading zeros, or <TT>~5,'*d</TT> to get leading asterisks. <P>
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In place of a prefix parameter to a directive, <TT>V</TT> (or <TT>v</TT>) can be used. In this case, <A REL=DEFINITION HREF="f_format.htm#format"><B>format</B></A> takes an argument from <I>args</I> as a parameter to the directive. The argument should be an <A REL=DEFINITION HREF="26_glo_i.htm#integer"><I>integer</I></A> or <A REL=DEFINITION HREF="26_glo_c.htm#character"><I>character</I></A>. If the <I>arg</I> used by a <TT>V</TT> parameter is <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>, the effect is as if the parameter had been omitted. <TT>#</TT> can be used in place of a prefix parameter; it represents the number of <I>args</I> remaining to be processed. When used within a recursive format, in the context of <TT>~?</TT> or <TT>~{</TT>, the <TT>#</TT> prefix parameter represents the number of <A REL=DEFINITION HREF="26_glo_f.htm#format_argument"><I>format arguments</I></A> remaining within the recursive call. <P>
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Examples of <A REL=DEFINITION HREF="26_glo_f.htm#format_string"><I>format strings</I></A>: <P>
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<PRE>
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"~S" ;This is an S directive with no parameters or modifiers.
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"~3,-4:@s" ;This is an S directive with two parameters, 3 and -4,
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; and both the <A REL=DEFINITION HREF="26_glo_c.htm#colon">colon</A> and <A REL=DEFINITION HREF="26_glo_a.htm#at-sign">at-sign</A> flags.
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"~,+4S" ;Here the first prefix parameter is omitted and takes
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; on its default value, while the second parameter is 4.
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</PRE>
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<P><B>Figure 22-6. Examples of format control strings</B> <P>
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<A REL=DEFINITION HREF="f_format.htm#format"><B>format</B></A> sends the output to <I>destination</I>. If <I>destination</I> is <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>, <A REL=DEFINITION HREF="f_format.htm#format"><B>format</B></A> creates and returns a <A REL=DEFINITION HREF="26_glo_s.htm#string"><I>string</I></A> containing the output from <I>control-string</I>. If <I>destination</I> is <A REL=DEFINITION HREF="26_glo_n.htm#non-nil"><I>non-nil</I></A>, it must be a <A REL=DEFINITION HREF="26_glo_s.htm#string"><I>string</I></A> with a <A REL=DEFINITION HREF="26_glo_f.htm#fill_pointer"><I>fill pointer</I></A>, a <A REL=DEFINITION HREF="26_glo_s.htm#stream"><I>stream</I></A>, or the symbol <A REL=DEFINITION HREF="a_t.htm#t"><B>t</B></A>. If <I>destination</I> is a <A REL=DEFINITION HREF="26_glo_s.htm#string"><I>string</I></A> with a <A REL=DEFINITION HREF="26_glo_f.htm#fill_pointer"><I>fill pointer</I></A>, the output is added to the end of the <A REL=DEFINITION HREF="26_glo_s.htm#string"><I>string</I></A>. If <I>destination</I> is a <A REL=DEFINITION HREF="26_glo_s.htm#stream"><I>stream</I></A>, the output is sent to that <A REL=DEFINITION HREF="26_glo_s.htm#stream"><I>stream</I></A>. If <I>destination</I> is <A REL=DEFINITION HREF="a_t.htm#t"><B>t</B></A>, the output is sent to <A REL=DEFINITION HREF="26_glo_s.htm#standard_output"><I>standard output</I></A>. <P>
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In the description of the directives that follows, the term <I>arg</I> in general refers to the next item of the set of <I>args</I> to be processed. The word or phrase at the beginning of each description is a mnemonic for the directive. <A REL=DEFINITION HREF="f_format.htm#format"><B>format</B></A> directives do not bind any of the printer control variables (<B>*print-...*</B>) except as specified in the following descriptions. Implementations may specify the binding of new, implementation-specific printer control variables for each <A REL=DEFINITION HREF="f_format.htm#format"><B>format</B></A> directive, but they may neither bind any standard printer control variables not specified in description of a <A REL=DEFINITION HREF="f_format.htm#format"><B>format</B></A> directive nor fail to bind any standard printer control variables as specified in the description. <P>
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<A REL=CHILD HREF="22_ca.htm"><H2>
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22.3.1 FORMAT Basic Output</H2></A><P>
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<A REL=CHILD HREF="22_cb.htm"><H2>
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22.3.2 FORMAT Radix Control</H2></A><P>
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<A REL=CHILD HREF="22_cc.htm"><H2>
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22.3.3 FORMAT Floating-Point Printers</H2></A><P>
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<A REL=CHILD HREF="22_cd.htm"><H2>
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22.3.4 FORMAT Printer Operations</H2></A><P>
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<A REL=CHILD HREF="22_ce.htm"><H2>
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22.3.5 FORMAT Pretty Printer Operations</H2></A><P>
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<A REL=CHILD HREF="22_cf.htm"><H2>
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22.3.6 FORMAT Layout Control</H2></A><P>
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<A REL=CHILD HREF="22_cg.htm"><H2>
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22.3.7 FORMAT Control-Flow Operations</H2></A><P>
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<A REL=CHILD HREF="22_ch.htm"><H2>
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22.3.8 FORMAT Miscellaneous Operations</H2></A><P>
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<A REL=CHILD HREF="22_ci.htm"><H2>
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22.3.9 FORMAT Miscellaneous Pseudo-Operations</H2></A><P>
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<A REL=CHILD HREF="22_cj.htm"><H2>
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22.3.10 Additional Information about FORMAT Operations</H2></A><P>
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<A REL=CHILD HREF="22_ck.htm"><H2>
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22.3.11 Examples of FORMAT</H2></A><P>
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<A REL=CHILD HREF="22_cl.htm"><H2>
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22.3.12 Notes about FORMAT</H2></A><P><P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issues</A>, <I>not part of the specification</I>, apply to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss169.htm">FORMAT-PRETTY-PRINT:YES</A><LI> <A REL=CHILD HREF="../Issues/iss164.htm">FORMAT-ATSIGN-COLON</A><LI> <A REL=CHILD HREF="../Issues/iss270.htm">PRETTY-PRINT-INTERFACE</A><P></UL><HR>
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<A REL=COPYRIGHT HREF="../Front/Help.htm#Legal"><I>Copyright 1996-2005, LispWorks Ltd. All rights reserved.</I></A><P>
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