path: root/lib/erl_interface/doc/src/erl_format.xml

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<cref>
  <header>
    <copyright>
      <year>1996</year><year>2016</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at

          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
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    </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>1996-10-16</date>
    <rev>A</rev>
    <file>erl_format.xml</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 since=""><ret>ETERM *</ret><nametext>erl_format(FormatStr, ...)</nametext></name>
      <fsummary>Create an Erlang term.</fsummary>
      <type>
        <v>char *FormatStr;</v>
      </type>
      <desc>
        <p>A general function for creating Erlang terms using
          a format specifier and a corresponding set of arguments, much
          in the way <c>printf()</c> works.</p>
        <p><c>FormatStr</c> is a format specification string.
          The valid format specifiers are as follows:</p>
        <list type="bulleted">
          <item><c>~i</c> - Integer</item>
          <item><c>~f</c> - Floating point</item>
          <item><c>~a</c> - Atom</item>
          <item><c>~s</c> - String</item>
          <item><c>~w</c> - Arbitrary Erlang term</item>
        </list>
        <p>For each format specifier included in <c>FormatStr</c>,
          there must be a corresponding argument following
          <c>FormatStr</c>. An Erlang term is built according to
          <c>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 creates an <c>(ETERM *)</c> structure corresponding
          to the Erlang term
          <c>[{name,madonna},{age,21},{data,[{adr,"E-street",42}]}]</c></p>
        <p>The function returns an Erlang term, or <c>NULL</c> if
          <c>FormatStr</c> does not describe a valid Erlang
          term.</p>
      </desc>
    </func>

    <func>
      <name since=""><ret>int</ret><nametext>erl_match(Pattern, Term)</nametext></name>
      <fsummary>Perform 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. For matching rules and more examples, see
          section <seealso marker="doc/reference_manual:patterns">
          Pattern Matching</seealso> in the Erlang Reference Manual.</p>
        <list type="bulleted">
          <item><c>Pattern</c> is an Erlang term, possibly
            containing unbound variables.</item>
          <item><c>Term</c> is an Erlang term that we wish to match
            against <c>Pattern</c>.</item>
        </list>
        <p><c>Term</c> and <c>Pattern</c> are compared
          and any unbound variables in <c>Pattern</c> are bound to
          corresponding values in <c>Term</c>.</p>
        <p>If <c>Term</c> and <c>Pattern</c> can be
          matched, the function returns a non-zero value and binds any unbound
          variables in <c>Pattern</c>. If <c>Term</c>
          and <c>Pattern</c> do
          not match, <c>0</c> is returned. 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>erl_var_content()</c> can be used to retrieve the
          content of any variables bound as a result of a call to
          <c>erl_match()</c>.</p>
      </desc>
    </func>
  </funcs>
</cref>