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<HTML><HEAD><TITLE>Recipe 4.5. Iterating Over an Array by Reference (Perl Cookbook)</TITLE><METANAME="DC.title"CONTENT="Perl Cookbook"><METANAME="DC.creator"CONTENT="Tom Christiansen & Nathan Torkington"><METANAME="DC.publisher"CONTENT="O'Reilly & Associates, Inc."><METANAME="DC.date"CONTENT="1999-07-02T01:31:25Z"><METANAME="DC.type"CONTENT="Text.Monograph"><METANAME="DC.format"CONTENT="text/html"SCHEME="MIME"><METANAME="DC.source"CONTENT="1-56592-243-3"SCHEME="ISBN"><METANAME="DC.language"CONTENT="en-US"><METANAME="generator"CONTENT="Jade 1.1/O'Reilly DocBook 3.0 to HTML 4.0"><LINKREV="made"HREF="mailto:online-books@oreilly.com"TITLE="Online Books Comments"><LINKREL="up"HREF="ch04_01.htm"TITLE="4. Arrays"><LINKREL="prev"HREF="ch04_05.htm"TITLE="4.4. Doing Something with Every Element in a List"><LINKREL="next"HREF="ch04_07.htm"TITLE="4.6. Extracting Unique Elements from a List"></HEAD><BODYBGCOLOR="#FFFFFF"><img alt="Book Home" border="0" src="gifs/smbanner.gif" usemap="#banner-map" /><map name="banner-map"><area shape="rect" coords="1,-2,616,66" href="index.htm" alt="Perl Cookbook"><area shape="rect" coords="629,-11,726,25" href="jobjects/fsearch.htm" alt="Search this book" /></map><div class="navbar"><p><TABLEWIDTH="684"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch04_05.htm"TITLE="4.4. Doing Something with Every Element in a List"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 4.4. Doing Something with Every Element in a List"BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="228"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1"><ACLASS="chapter"REL="up"HREF="ch04_01.htm"TITLE="4. Arrays"></A></FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch04_07.htm"TITLE="4.6. Extracting Unique Elements from a List"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 4.6. Extracting Unique Elements from a List"BORDER="0"></A></TD></TR></TABLE></DIV><DIVCLASS="sect1"><H2CLASS="sect1"><ACLASS="title"NAME="ch04-98198">4.5. Iterating Over an Array by Reference</A></H2><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch04-pgfId-577">Problem <ACLASS="indexterm"NAME="ch04-idx-1000006639-0"></A><ACLASS="indexterm"NAME="ch04-idx-1000006639-1"></A></A></H3><PCLASS="para">You have a reference to an array, and you want to use <CODECLASS="literal">foreach</CODE> to work with the array's elements.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch04-pgfId-583">Solution</A></H3><PCLASS="para">Use <CODECLASS="literal">foreach</CODE> or <CODECLASS="literal">for</CODE> to loop over the dereferenced array:</P><PRECLASS="programlisting"># iterate over elements of array in $ARRAYREFforeach $item (@$ARRAYREF) { # do something with $item}for ($i = 0; $i <= $#$ARRAYREF; $i++) { # do something with $ARRAYREF->[$i]}</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch04-pgfId-605">Discussion</A></H3><PCLASS="para">The solutions assume you have a scalar variable containing the array reference. This lets you do things like this:</P><PRECLASS="programlisting">@fruits = ( "Apple", "Blackberry" );$fruit_ref = \@fruits;foreach $fruit (@$fruit_ref) { print "$fruit tastes good in a pie.\n";}<CODECLASS="userinput"><B><CODECLASS="replaceable"><I>Apple tastes good in a pie.</I></CODE></B></CODE><CODECLASS="userinput"><B><CODECLASS="replaceable"><I>Blackberry tastes good in a pie.</I></CODE></B></CODE></PRE><PCLASS="para">We could have rewritten the <CODECLASS="literal">foreach</CODE> loop as a <CODECLASS="literal">for</CODE> loop like this:</P><PRECLASS="programlisting">for ($i=0; $i <= $#$fruit_ref; $i++) { print "$fruit_ref->[$i] tastes good in a pie.\n";}</PRE><PCLASS="para">Frequently, though, the array reference is the result of a more complex expression. You need to use the <CODECLASS="literal">@{</CODE> <CODECLASS="literal">EXPR</CODE> <CODECLASS="literal">}</CODE> notation to turn the result of the expression back into an array:</P><PRECLASS="programlisting">$namelist{felines} = \@rogue_cats;foreach $cat ( @{ $namelist{felines} } ) { print "$cat purrs hypnotically..\n";}print "--More--\nYou are controlled.\n";</PRE><PCLASS="para">Again, we can replace the <CODECLASS="literal">foreach</CODE> with a <CODECLASS="literal">for</CODE> loop:</P><PRECLASS="programlisting">for ($i=0; $i <= $#{ $namelist{felines} }; $i++) { print "$namelist{felines}[$i] purrs hypnotically.\n";}</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch04-pgfId-653">See Also</A></H3><PCLASS="para"><ICLASS="filename">perlref </I><ACLASS="indexterm"NAME="ch04-idx-1000006648-0"></A><ACLASS="indexterm"NAME="ch04-idx-1000006648-1"></A><EMCLASS="emphasis"> </EM>(1) and <EMCLASS="emphasis">perllol </EM>(1); <ACLASS="olink"HREF="../prog/ch04_01.htm">Chapter 4</A> of <ACLASS="citetitle"HREF="../prog/index.htm"TITLE="Programming Perl"><CITECLASS="citetitle">Programming Perl</CITE></A>; <ACLASS="xref"HREF="ch11_02.htm"TITLE="Taking References to Arrays">Recipe 11.1</A>; <ACLASS="xref"HREF="ch04_05.htm"TITLE="Doing Something with Every Element in a List">Recipe 4.4</A> <ACLASS="indexterm"NAME="ch04-idx-1000006641-0"></A></P></DIV></DIV><DIVCLASS="htmlnav"><P></P><HRALIGN="LEFT"WIDTH="684"TITLE="footer"><TABLEWIDTH="684"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch04_05.htm"TITLE="4.4. Doing Something with Every Element in a List"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 4.4. Doing Something with Every Element in a List"BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="228"><ACLASS="book"HREF="index.htm"TITLE="Perl Cookbook"><IMGSRC="../gifs/txthome.gif"ALT="Perl Cookbook"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch04_07.htm"TITLE="4.6. Extracting Unique Elements from a List"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 4.6. Extracting Unique Elements from a List"BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228">4.4. Doing Something with Every Element in a List</TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="228"><ACLASS="index"HREF="index/index.htm"TITLE="Book Index"><IMGSRC="../gifs/index.gif"ALT="Book Index"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="228">4.6. 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