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<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE cref SYSTEM "cref.dtd">
<cref>
<header>
<copyright>
<year>1996</year><year>2013</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
limitations under the License.
</legalnotice>
<title>erl_format</title>
<prepared>Torbjörn Törnkvist</prepared>
<responsible>Torbjörn Törnkvist</responsible>
<docno></docno>
<approved>Bjarne Däcker</approved>
<checked>Torbjörn Törnkvist</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>
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