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<HTML><HEAD><TITLE>Recipe 1.4. Converting Between ASCII Characters and Values (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="1999-07-02T01:28:49Z"><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="ch01_01.htm"TITLE="1. Strings"><LINKREL="prev"HREF="ch01_04.htm"TITLE="1.3. Exchanging Values Without Using Temporary Variables"><LINKREL="next"HREF="ch01_06.htm"TITLE="1.5. Processing a String One Character at a Time"></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="ch01_04.htm"TITLE="1.3. Exchanging Values Without Using Temporary Variables"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 1.3. Exchanging Values Without Using Temporary Variables"BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="228"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1"><ACLASS="chapter"REL="up"HREF="ch01_01.htm"TITLE="1. Strings"></A></FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch01_06.htm"TITLE="1.5. Processing a String One Character at a Time"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 1.5. Processing a String One Character at a Time"BORDER="0"></A></TD></TR></TABLE></DIV><DIVCLASS="sect1"><H2CLASS="sect1"><ACLASS="title"NAME="ch01-42021">1.4. Converting Between ASCII Characters and Values</A></H2><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch01-pgfId-449">Problem <ACLASS="indexterm"NAME="ch01-idx-1000010195-0"></A><ACLASS="indexterm"NAME="ch01-idx-1000010195-1"></A><ACLASS="indexterm"NAME="ch01-idx-1000010195-2"></A><ACLASS="indexterm"NAME="ch01-idx-1000010195-3"></A><ACLASS="indexterm"NAME="ch01-idx-1000010195-4"></A></A></H3><PCLASS="para">You want to print out the number represented by a given ASCII character, or you want to print out an ASCII character given a number.<ACLASS="indexterm"NAME="ch01-idx-1000010205-0"></A><ACLASS="indexterm"NAME="ch01-idx-1000010205-1"></A></P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch01-pgfId-455">Solution</A></H3><PCLASS="para">Use <CODECLASS="literal">ord</CODE> to convert a character to a number, or use <CODECLASS="literal">chr</CODE> to convert a number to a character:</P><PRECLASS="programlisting">$num = ord($char);$char = chr($num);</PRE><PCLASS="para">The <CODECLASS="literal">%c</CODE> format used in <CODECLASS="literal">printf</CODE> and <CODECLASS="literal">sprintf</CODE> also converts a number to a character:</P><PRECLASS="programlisting">$char = sprintf("%c", $num); # slower than chr($num)printf("Number %d is character %c\n", $num, $num);<CODECLASS="userinput"><B><CODECLASS="replaceable"><I>Number 101 is character e</I></CODE></B></CODE></PRE><PCLASS="para">A <CODECLASS="literal">C*</CODE> template used with <CODECLASS="literal">pack</CODE> and <CODECLASS="literal">unpack</CODE> can quickly convert many characters.</P><PRECLASS="programlisting">@ASCII = unpack("C*", $string);$STRING = pack("C*", @ascii);</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch01-pgfId-479">Discussion</A></H3><PCLASS="para">Unlike low-level, typeless languages like assembler, Perl doesn't treat characters and numbers interchangeably; it treats <EMCLASS="emphasis">strings</EM> and numbers interchangeably. That means you can't just assign characters and numbers back and forth. Perl provides Pascal's <CODECLASS="literal">chr</CODE><ACLASS="indexterm"NAME="ch01-idx-1000010206-0"></A><ACLASS="indexterm"NAME="ch01-idx-1000010206-1"></A> and <CODECLASS="literal">ord</CODE> to convert between a character and its corresponding ordinal value:</P><PRECLASS="programlisting">$ascii_value = ord("e"); # now 101$character = chr(101); # now "e"</PRE><PCLASS="para">If you already have a character, it's really represented as a string of length one, so just print it out directly using <CODECLASS="literal">print</CODE> or the <CODECLASS="literal">%s</CODE> format in <CODECLASS="literal">printf</CODE> and <CODECLASS="literal">sprintf</CODE>. The <CODECLASS="literal">%c</CODE><ACLASS="indexterm"NAME="ch01-idx-1000010207-0"></A><ACLASS="indexterm"NAME="ch01-idx-1000010207-1"></A><ACLASS="indexterm"NAME="ch01-idx-1000010207-2"></A> format forces <CODECLASS="literal">printf</CODE> or <CODECLASS="literal">sprintf</CODE> to convert a number into a character; it's not used for printing a character that's already in character format (that is, a string).</P><PRECLASS="programlisting">printf("Number %d is character %c\n", 101, 101);</PRE><PCLASS="para">The <CODECLASS="literal">pack</CODE><ACLASS="indexterm"NAME="ch01-idx-1000010208-0"></A><ACLASS="indexterm"NAME="ch01-idx-1000010208-1"></A>, <CODECLASS="literal">unpack</CODE>, <CODECLASS="literal">chr</CODE>, and <CODECLASS="literal">ord</CODE> functions are all faster than <CODECLASS="literal">sprintf</CODE>. Here are <CODECLASS="literal">pack</CODE> and <CODECLASS="literal">unpack</CODE> in action:</P><PRECLASS="programlisting">@ascii_character_numbers = unpack("C*", "sample");print "@ascii_character_numbers\n";<CODECLASS="userinput"><B><CODECLASS="replaceable"><I>115 97 109 112 108 101</I></CODE></B></CODE>$word = pack("C*", @ascii_character_numbers);$word = pack("C*", 115, 97, 109, 112, 108, 101); # sameprint "$word\n";<CODECLASS="userinput"><B><CODECLASS="replaceable"><I>sample</I></CODE></B></CODE></PRE><PCLASS="para">Here's how to convert from HAL to IBM:</P><PRECLASS="programlisting">$hal = "HAL";@ascii = unpack("C*", $hal);foreach $val (@ascii) { $val++; # add one to each ASCII value}$ibm = pack("C*", @ascii);print "$ibm\n"; # prints "IBM"</PRE><PCLASS="para">The <CODECLASS="literal">ord</CODE> function can return numbers from 0 to 255. These correspond to C's <CODECLASS="literal">unsigned</CODE> <CODECLASS="literal">char</CODE> data type.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch01-pgfId-529">See Also</A></H3><PCLASS="para">The <CODECLASS="literal">chr</CODE>, <CODECLASS="literal">ord</CODE>, <CODECLASS="literal">printf</CODE>, <CODECLASS="literal">sprintf</CODE>, <CODECLASS="literal">pack</CODE>, and <CODECLASS="literal">unpack</CODE> functions in <EMCLASS="emphasis">perlfunc </EM>(1) and <ACLASS="olink"HREF="../prog/ch03_01.htm">Chapter 3</A> of <ACLASS="citetitle"HREF="../prog/index.htm"TITLE="Programming Perl"><CITECLASS="citetitle">Programming Perl</CITE></A><ACLASS="indexterm"NAME="ch01-idx-1000010197-0"></A><ACLASS="indexterm"NAME="ch01-idx-1000010197-1"></A><ACLASS="indexterm"NAME="ch01-idx-1000010197-2"></A><ACLASS="indexterm"NAME="ch01-idx-1000010197-3"></A><ACLASS="indexterm"NAME="ch01-idx-1000010197-4"></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="ch01_04.htm"TITLE="1.3. 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