67 lines
7.5 KiB
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67 lines
7.5 KiB
HTML
<!-- Common Lisp HyperSpec (TM), version 7.0 generated by Kent M. Pitman on Mon, 11-Apr-2005 2:31am EDT -->
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<TITLE>CLHS: Function READ-FROM-STRING</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="f_rd_del.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_reader.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="f_rdtabl.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<A NAME="read-from-string"><I>Function</I> <B>READ-FROM-STRING</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>read-from-string</B> <I>string <TT>&optional</TT> eof-error-p eof-value <TT>&key</TT> start end preserve-whitespace</I><P> => <I>object, position</I><P>
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<P>
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<P><B>Arguments and Values:</B><P>
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<P>
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<I>string</I>---a <A REL=DEFINITION HREF="26_glo_s.htm#string"><I>string</I></A>. <P>
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<I>eof-error-p</I>---a <A REL=DEFINITION HREF="26_glo_g.htm#generalized_boolean"><I>generalized boolean</I></A>. The default is <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A>. <P>
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<I>eof-value</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. The default is <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>. <P>
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<I>start</I>, <I>end</I>---<A REL=DEFINITION HREF="26_glo_b.htm#bounding_index_designator"><I>bounding index designators</I></A> of <I>string</I>. The defaults for <I>start</I> and <I>end</I> are <TT>0</TT> and <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>, respectively. <P>
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<I>preserve-whitespace</I>---a <A REL=DEFINITION HREF="26_glo_g.htm#generalized_boolean"><I>generalized boolean</I></A>. The default is <A REL=DEFINITION HREF="26_glo_f.htm#false"><I>false</I></A>. <P>
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<I>object</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A> (parsed by the <A REL=DEFINITION HREF="26_glo_l.htm#lisp_reader"><I>Lisp reader</I></A>) or the <I>eof-value</I>. <P>
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<I>position</I>---an <A REL=DEFINITION HREF="26_glo_i.htm#integer"><I>integer</I></A> greater than or equal to zero, and less than or equal to one more than the <A REL=DEFINITION HREF="26_glo_l.htm#length"><I>length</I></A> of the <I>string</I>. <P>
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<P><B>Description:</B><P>
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<P>
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Parses the printed representation of an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A> from the subsequence of <I>string</I> <A REL=DEFINITION HREF="26_glo_b.htm#bounded"><I>bounded</I></A> by <I>start</I> and <I>end</I>, as if <A REL=DEFINITION HREF="f_rd_rd.htm#read"><B>read</B></A> had been called on an <A REL=DEFINITION HREF="26_glo_i.htm#input"><I>input</I></A> <A REL=DEFINITION HREF="26_glo_s.htm#stream"><I>stream</I></A> containing those same <A REL=DEFINITION HREF="26_glo_c.htm#character"><I>characters</I></A>. <P>
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If <I>preserve-whitespace</I> is <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A>, the operation will preserve <A REL=DEFINITION HREF="26_glo_w.htm#whitespace"><I>whitespace</I></A>[2] as <A REL=DEFINITION HREF="f_rd_rd.htm#read-preserving-whitespace"><B>read-preserving-whitespace</B></A> would do. <P>
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If an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A> is successfully parsed, the <A REL=DEFINITION HREF="26_glo_p.htm#primary_value"><I>primary value</I></A>, <I>object</I>, is the <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A> that was parsed. If <I>eof-error-p</I> is <A REL=DEFINITION HREF="26_glo_f.htm#false"><I>false</I></A> and if the end of the <I>substring</I> is reached, <I>eof-value</I> is returned. <P>
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The <A REL=DEFINITION HREF="26_glo_s.htm#secondary_value"><I>secondary value</I></A>, <I>position</I>, is the index of the first <A REL=DEFINITION HREF="26_glo_c.htm#character"><I>character</I></A> in the <A REL=DEFINITION HREF="26_glo_b.htm#bounded"><I>bounded</I></A> <I>string</I> that was not read. The <I>position</I> may depend upon the value of <I>preserve-whitespace</I>. If the entire <I>string</I> was read, the <I>position</I> returned is either the <I>length</I> of the <I>string</I> or one greater than the <I>length</I> of the <I>string</I>. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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(read-from-string " 1 3 5" t nil :start 2) => 3, 5
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(read-from-string "(a b c)") => (A B C), 7
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</PRE>
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</TT> <P>
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<P><B>Side Effects:</B> None.
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<P>
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<P><B>Affected By:</B> None.
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<P>
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<P><B>Exceptional Situations:</B><P>
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<P>
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If the end of the supplied substring occurs before an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A> can be read, an error is signaled if <I>eof-error-p</I> is <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A>. An error is signaled if the end of the <I>substring</I> occurs in the middle of an incomplete <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. <P>
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<P><B>See Also:</B><P>
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<P>
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<A REL=DEFINITION HREF="f_rd_rd.htm#read"><B>read</B></A>, <A REL=DEFINITION HREF="f_rd_rd.htm#read-preserving-whitespace"><B>read-preserving-whitespace</B></A> <P>
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<P><B>Notes:</B><P>
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<P>
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The reason that <I>position</I> is allowed to be beyond the <A REL=DEFINITION HREF="26_glo_l.htm#length"><I>length</I></A> of the <I>string</I> is to permit (but not require) the <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementation</I></A> to work by simulating the effect of a trailing delimiter at the end of the <A REL=DEFINITION HREF="26_glo_b.htm#bounded"><I>bounded</I></A> <I>string</I>. When <I>preserve-whitespace</I> is <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A>, the <I>position</I> might count the simulated delimiter. <P>
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<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/iss284.htm">RANGE-OF-START-AND-END-PARAMETERS:INTEGER-AND-INTEGER-NIL</A><LI> <A REL=CHILD HREF="../Issues/iss332.htm">SUBSEQ-OUT-OF-BOUNDS</A><LI> <A REL=CHILD HREF="../Issues/iss013.htm">ARGUMENTS-UNDERSPECIFIED:SPECIFY</A><P></UL><HR>
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