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<!DOCTYPE cref SYSTEM "cref.dtd">

<cref>
  <header>
    <copyright>
      <year>1996</year><year>2009</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      The contents of this file are subject to the Erlang Public License,
      Version 1.1, (the "License"); you may not use this file except in
      compliance with the License. You should have received a copy of the
      Erlang Public License along with this software. If not, it can be
      retrieved online at http://www.erlang.org/.
    
      Software distributed under the License is distributed on an "AS IS"
      basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
      the License for the specific language governing rights and limitations
      under the License.
    
    </legalnotice>

    <title>erl_format</title>
    <prepared>Torbj&ouml;rn T&ouml;rnkvist</prepared>
    <responsible>Torbj&ouml;rn T&ouml;rnkvist</responsible>
    <docno></docno>
    <approved>Bjarne D&auml;cker</approved>
    <checked>Torbj&ouml;rn T&ouml;rnkvist</checked>
    <date>961016</date>
    <rev>A</rev>
    <file>erl_format.sgml</file>
  </header>
  <lib>erl_format</lib>
  <libsummary>Create and Match Erlang Terms</libsummary>
  <description>
    <p>This module contains two routines - one general function for
      creating Erlang terms and one for pattern matching Erlang terms.</p>
  </description>
  <funcs>
    <func>
      <name><ret>ETERM *</ret><nametext>erl_format(FormatStr, ... )</nametext></name>
      <fsummary>Creates an Erlang term</fsummary>
      <type>
        <v>char *FormatStr;</v>
      </type>
      <desc>
        <p>This is a general function for creating Erlang terms using
          a format specifier and a corresponding set of arguments, much
          in the way <c><![CDATA[printf()]]></c> works.</p>
        <p><c><![CDATA[FormatStr]]></c> is a format specification string. The set
          of valid format specifiers is as follows:</p>
        <list type="bulleted">
          <item>
            <p>~i - Integer</p>
          </item>
          <item>
            <p>~f - Floating point</p>
          </item>
          <item>
            <p>~a - Atom</p>
          </item>
          <item>
            <p>~s - String</p>
          </item>
          <item>
            <p>~w - Arbitrary Erlang term</p>
          </item>
        </list>
        <p>For each format specifier that appears in <c><![CDATA[FormatStr]]></c>,
          there must be a corresponding argument following
          <c><![CDATA[FormatStr]]></c>. An Erlang term is built according to the
          <c><![CDATA[FormatStr]]></c> with values and Erlang terms substituted from
          the corresponding arguments and according to the individual
          format specifiers. For example:</p>
        <code type="none"><![CDATA[
erl_format("[{name,~a},{age,~i},{data,~w}]",
           "madonna",
           21,
           erl_format("[{adr,~s,~i}]","E-street",42));
        ]]></code>
        <p>This will create an <c><![CDATA[(ETERM *)]]></c> structure corresponding
          to the Erlang term: 
          <c><![CDATA[[{name,madonna},{age,21},{data,[{adr,"E-street",42}]}]]]></c></p>
        <p>The function returns an Erlang term, or NULL if
          <c><![CDATA[FormatStr]]></c> does not describe a valid Erlang term.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>erl_match(Pattern, Term)</nametext></name>
      <fsummary>Performs pattern matching</fsummary>
      <type>
        <v>ETERM *Pattern,*Term;</v>
      </type>
      <desc>
        <p>This function is used to perform pattern matching similar
          to that done in Erlang. Refer to an Erlang manual for matching
          rules and more examples.</p>
        <p><c><![CDATA[Pattern]]></c> is an Erlang term, possibly containing unbound
          variables. </p>
        <p><c><![CDATA[Term]]></c> is an Erlang term that we wish to match against
          <c><![CDATA[Pattern]]></c>.</p>
        <p><c><![CDATA[Term]]></c> and <c><![CDATA[Pattern]]></c> are compared, and any
          unbound variables in <c><![CDATA[Pattern]]></c> are bound to corresponding
          values in <c><![CDATA[Term]]></c>. </p>
        <p>If <c><![CDATA[Term]]></c> and <c><![CDATA[Pattern]]></c> can be matched, the
          function returns a non-zero value and binds any unbound
          variables in <c><![CDATA[Pattern]]></c>. If <c><![CDATA[Term]]></c><c><![CDATA[Pattern]]></c> do
          not match, the function returns 0. For example:</p>
        <code type="none"><![CDATA[
ETERM *term, *pattern, *pattern2;
term1    = erl_format("{14,21}");
term2    = erl_format("{19,19}");
pattern1 = erl_format("{A,B}");
pattern2 = erl_format("{F,F}");
if (erl_match(pattern1, term1)) {
  /* match succeeds:
   * A gets bound to 14, 
   * B gets bound to 21 
   */
  ...  
}
if (erl_match(pattern2, term1)) {
  /* match fails because F cannot be 
   * bound to two separate values, 14 and 21
   */
  ...
}
if (erl_match(pattern2, term2)) {
  /* match succeeds and F gets bound to 19 */
  ...
}
        ]]></code>
        <p><c><![CDATA[erl_var_content()]]></c> can be used to retrieve the
          content of any variables bound as a result of a call to
          <c><![CDATA[erl_match()]]></c>.</p>
      </desc>
    </func>
  </funcs>
</cref>

