67 lines
6.2 KiB
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67 lines
6.2 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-CHAR</TITLE>
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<A NAME="read-char"><I>Function</I> <B>READ-CHAR</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>read-char</B> <I><TT>&optional</TT> input-stream eof-error-p eof-value recursive-p</I> => <I>char</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>input-stream</I>---an <A REL=DEFINITION HREF="26_glo_i.htm#input"><I>input</I></A> <A REL=DEFINITION HREF="26_glo_s.htm#stream_designator"><I>stream designator</I></A>. The default is <A REL=DEFINITION HREF="26_glo_s.htm#standard_input"><I>standard input</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>recursive-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_f.htm#false"><I>false</I></A>. <P>
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<I>char</I>---a <A REL=DEFINITION HREF="26_glo_c.htm#character"><I>character</I></A> or the <I>eof-value</I>. <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="#read-char"><B>read-char</B></A> returns the next <A REL=DEFINITION HREF="26_glo_c.htm#character"><I>character</I></A> from <I>input-stream</I>. <P>
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When <I>input-stream</I> is an <I>echo stream</I>, the character is echoed on <I>input-stream</I> the first time the character is seen. Characters that are not echoed by <A REL=DEFINITION HREF="#read-char"><B>read-char</B></A> are those that were put there by <A REL=DEFINITION HREF="f_unrd_c.htm#unread-char"><B>unread-char</B></A> and hence are assumed to have been echoed already by a previous call to <A REL=DEFINITION HREF="#read-char"><B>read-char</B></A>. <P>
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If <I>recursive-p</I> is <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A>, this call is expected to be embedded in a higher-level call to <A REL=DEFINITION HREF="f_rd_rd.htm#read"><B>read</B></A> or a similar <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> used by the <A REL=DEFINITION HREF="26_glo_l.htm#lisp_reader"><I>Lisp reader</I></A>. <P>
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If an <A REL=DEFINITION HREF="26_glo_e.htm#end_of_file"><I>end of file</I></A>[2] occurs and <I>eof-error-p</I> is <A REL=DEFINITION HREF="26_glo_f.htm#false"><I>false</I></A>, <I>eof-value</I> is returned. <P>
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<P><B>Examples:</B><P>
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<PRE>
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(with-input-from-string (is "0123")
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(do ((c (read-char is) (read-char is nil 'the-end)))
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((not (characterp c)))
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(format t "~S " c)))
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>> #\0 #\1 #\2 #\3
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=> NIL
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</PRE>
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</TT> <P>
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<P><B>Affected By:</B><P>
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<P>
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<A REL=DEFINITION HREF="v_debug_.htm#STstandard-inputST"><B>*standard-input*</B></A>, <A REL=DEFINITION HREF="v_termin.htm#STterminal-ioST"><B>*terminal-io*</B></A>. <P>
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<P><B>Exceptional Situations:</B><P>
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<P>
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If an <A REL=DEFINITION HREF="26_glo_e.htm#end_of_file"><I>end of file</I></A>[2] occurs before a character can be read, and <I>eof-error-p</I> is <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A>, an error of <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A> <A REL=DEFINITION HREF="e_end_of.htm#end-of-file"><B>end-of-file</B></A> is signaled. <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_by.htm#read-byte"><B>read-byte</B></A>, <A REL=DEFINITION HREF="f_rd_seq.htm#read-sequence"><B>read-sequence</B></A>, <A REL=DEFINITION HREF="f_wr_cha.htm#write-char"><B>write-char</B></A>, <A REL=DEFINITION HREF="f_rd_rd.htm#read"><B>read</B></A> <P>
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<P><B>Notes:</B><P>
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The corresponding output function is <A REL=DEFINITION HREF="f_wr_cha.htm#write-char"><B>write-char</B></A>. <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/iss285.htm">READ-AND-WRITE-BYTES:NEW-FUNCTIONS</A><LI> <A REL=CHILD HREF="../Issues/iss268.htm">PEEK-CHAR-READ-CHAR-ECHO:FIRST-READ-CHAR</A><LI> <A REL=CHILD HREF="../Issues/iss013.htm">ARGUMENTS-UNDERSPECIFIED:SPECIFY</A><P></UL><HR>
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