path: root/lib/stdlib/doc/src/string.xml

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<erlref>
  <header>
    <copyright>
      <year>1996</year><year>2012</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>string</title>
    <prepared>Robert Virding</prepared>
    <responsible>Bjarne Dacker</responsible>
    <docno>1</docno>
    <approved>Bjarne D&auml;cker</approved>
    <checked></checked>
    <date>96-09-28</date>
    <rev>A</rev>
    <file>string.sgml</file>
  </header>
  <module>string</module>
  <modulesummary>String Processing Functions</modulesummary>
  <description>
    <p>This module contains functions for string processing.</p>
  </description>
  <funcs>
    <func>
      <name name="len" arity="1"/>
      <fsummary>Return the length of a string</fsummary>
      <desc>
        <p>Returns the number of characters in the string.</p>
      </desc>
    </func>
    <func>
      <name name="equal" arity="2"/>
      <fsummary>Test string equality</fsummary>
      <desc>
        <p>Tests whether two strings are equal. Returns <c>true</c> if
          they are, otherwise <c>false</c>.</p>
      </desc>
    </func>
    <func>
      <name name="concat" arity="2"/>
      <fsummary>Concatenate two strings</fsummary>
      <desc>
        <p>Concatenates two strings to form a new string. Returns the
          new string.</p>
      </desc>
    </func>
    <func>
      <name name="chr" arity="2"/>
      <name name="rchr" arity="2"/>
      <fsummary>Return the index of the first/last occurrence of<c>Character</c>in <c>String</c></fsummary>
      <desc>
        <p>Returns the index of the first/last occurrence of
          <c><anno>Character</anno></c> in <c><anno>String</anno></c>. <c>0</c> is returned if <c><anno>Character</anno></c> does not
          occur.</p>
      </desc>
    </func>
    <func>
      <name name="str" arity="2"/>
      <name name="rstr" arity="2"/>
      <fsummary>Find the index of a substring</fsummary>
      <desc>
        <p>Returns the position where the first/last occurrence of
          <c><anno>SubString</anno></c> begins in <c><anno>String</anno></c>. <c>0</c> is returned if <c><anno>SubString</anno></c>
          does not exist in <c><anno>String</anno></c>.
          For example:</p>
        <code type="none">
> string:str(" Hello Hello World World ", "Hello World").
8        </code>
      </desc>
    </func>
    <func>
      <name name="span" arity="2"/>
      <name name="cspan" arity="2"/>
      <fsummary>Span characters at start of string</fsummary>
      <desc>
        <p>Returns the length of the maximum initial segment of
          <c><anno>String</anno></c>, which consists entirely of characters from (not
          from) <c><anno>Chars</anno></c>.</p>
        <p>For example:</p>
        <code type="none">
> string:span("\t    abcdef", " \t").
5
> string:cspan("\t    abcdef", " \t").
0        </code>
      </desc>
    </func>
    <func>
      <name name="substr" arity="2"/>
      <name name="substr" arity="3"/>
      <fsummary>Return a substring of <c>String</c></fsummary>
      <desc>
        <p>Returns a substring of <c><anno>String</anno></c>, starting at the
          position <c><anno>Start</anno></c>, and ending at the end of the string or
          at length <c><anno>Length</anno></c>.</p>
        <p>For example:</p>
        <code type="none">
> substr("Hello World", 4, 5).
"lo Wo"        </code>
      </desc>
    </func>
    <func>
      <name name="tokens" arity="2"/>
      <fsummary>Split string into tokens</fsummary>
      <desc>
        <p>Returns a list of tokens in <c><anno>String</anno></c>, separated by the
          characters in <c><anno>SeparatorList</anno></c>.</p>
        <p>For example:</p>
        <code type="none">
> tokens("abc defxxghix jkl", "x ").
["abc", "def", "ghi", "jkl"]        </code>
      </desc>
    </func>
    <func>
      <name name="join" arity="2"/>
      <fsummary>Join a list of strings with separator</fsummary>
      <desc>
	<p>Returns a string with the elements of <c><anno>StringList</anno></c>
	  separated by the string in <c><anno>Separator</anno></c>.</p>
	<p>For example:</p>
	<code type="none">
> join(["one", "two", "three"], ", ").
"one, two, three"        </code>
      </desc>
    </func>
    <func>
      <name name="chars" arity="2"/>
      <name name="chars" arity="3"/>
      <fsummary>Returns a string consisting of numbers of characters</fsummary>
      <desc>
        <p>Returns a string consisting of <c><anno>Number</anno></c> of characters
          <c><anno>Character</anno></c>. Optionally, the string can end with the
          string <c><anno>Tail</anno></c>.</p>
      </desc>
    </func>
    <func>
      <name name="copies" arity="2"/>
      <fsummary>Copy a string</fsummary>
      <desc>
        <p>Returns a string containing <c><anno>String</anno></c> repeated
          <c><anno>Number</anno></c> times.</p>
      </desc>
    </func>
    <func>
      <name name="words" arity="1"/>
      <name name="words" arity="2"/>
      <fsummary>Count blank separated words</fsummary>
      <desc>
        <p>Returns the number of words in <c><anno>String</anno></c>, separated by
          blanks or <c><anno>Character</anno></c>.</p>
        <p>For example:</p>
        <code type="none">
> words(" Hello old boy!", $o).
4        </code>
      </desc>
    </func>
    <func>
      <name name="sub_word" arity="2"/>
      <name name="sub_word" arity="3"/>
      <fsummary>Extract subword</fsummary>
      <desc>
        <p>Returns the word in position <c><anno>Number</anno></c> of <c><anno>String</anno></c>.
          Words are separated by blanks or <c><anno>Character</anno></c>s.</p>
        <p>For example:</p>
        <code type="none">
> string:sub_word(" Hello old boy !",3,$o).
"ld b"        </code>
      </desc>
    </func>
    <func>
      <name name="strip" arity="1"/>
      <name name="strip" arity="2"/>
      <name name="strip" arity="3"/>
      <fsummary>Strip leading or trailing characters</fsummary>
      <desc>
        <p>Returns a string, where leading and/or trailing blanks or a
          number of <c><anno>Character</anno></c> have been removed.
          <c><anno>Direction</anno></c> can be <c>left</c>, <c>right</c>, or
          <c>both</c> and indicates from which direction blanks are to be
          removed. The function <c>strip/1</c> is equivalent to
          <c>strip(String, both)</c>.</p>
        <p>For example:</p>
        <code type="none">
> string:strip("...Hello.....", both, $.).
"Hello"        </code>
      </desc>
    </func>
    <func>
      <name name="left" arity="2"/>
      <name name="left" arity="3"/>
      <fsummary>Adjust left end of string</fsummary>
      <desc>
        <p>Returns the <c><anno>String</anno></c> with the length adjusted in
          accordance with <c><anno>Number</anno></c>. The left margin is
          fixed. If the <c>length(<anno>String</anno>)</c> &lt; <c><anno>Number</anno></c>,
          <c><anno>String</anno></c> is padded with blanks or <c><anno>Character</anno></c>s.</p>
        <p>For example:</p>
        <code type="none">
> string:left("Hello",10,$.).
"Hello....."        </code>
      </desc>
    </func>
    <func>
      <name name="right" arity="2"/>
      <name name="right" arity="3"/>
      <fsummary>Adjust right end of string</fsummary>
      <desc>
        <p>Returns the <c><anno>String</anno></c> with the length adjusted in
          accordance with <c><anno>Number</anno></c>. The right margin is
          fixed. If the length of <c>(<anno>String</anno>)</c> &lt; <c><anno>Number</anno></c>,
          <c><anno>String</anno></c> is padded with blanks or <c><anno>Character</anno></c>s.</p>
        <p>For example:</p>
        <code type="none">
> string:right("Hello", 10, $.).
".....Hello"        </code>
      </desc>
    </func>
    <func>
      <name name="centre" arity="2"/>
      <name name="centre" arity="3"/>
      <fsummary>Center a string</fsummary>
      <desc>
        <p>Returns a string, where <c><anno>String</anno></c> is centred in the
          string and surrounded by blanks or characters. The resulting
          string will have the length <c><anno>Number</anno></c>.</p>
      </desc>
    </func>
    <func>
      <name name="sub_string" arity="2"/>
      <name name="sub_string" arity="3"/>
      <fsummary>Extract a substring</fsummary>
      <desc>
        <p>Returns a substring of <c><anno>String</anno></c>, starting at the
          position <c><anno>Start</anno></c> to the end of the string, or to and
          including the <c><anno>Stop</anno></c> position.</p>
        <p>For example:</p>
        <code type="none">
sub_string("Hello World", 4, 8).
"lo Wo"        </code>
      </desc>
    </func>
    <func>
      <name name="to_float" arity="1"/>
      <fsummary>Returns a float whose text representation is the integers (ASCII values) in String.</fsummary>
      <desc>
        <p>Argument <c><anno>String</anno></c> is expected to start with a valid text
          represented float (the digits being ASCII values). Remaining characters 
          in the string after the float are returned in <c><anno>Rest</anno></c>.</p>
        <p>Example:</p>
        <code type="none">
          > {F1,Fs} = string:to_float("1.0-1.0e-1"),
          > {F2,[]} = string:to_float(Fs),
          > F1+F2.
          0.9
          > string:to_float("3/2=1.5").
          {error,no_float}
          > string:to_float("-1.5eX").
          {-1.5,"eX"}</code>
      </desc>
    </func>
    <func>
      <name name="to_integer" arity="1"/>
      <fsummary>Returns an integer whose text representation is the integers (ASCII values) in String.</fsummary>
      <desc>
        <p>Argument <c><anno>String</anno></c> is expected to start with a valid text
          represented integer (the digits being ASCII values). Remaining characters 
          in the string after the integer are returned in <c><anno>Rest</anno></c>.</p>
        <p>Example:</p>
        <code type="none">
          > {I1,Is} = string:to_integer("33+22"),
          > {I2,[]} = string:to_integer(Is),
          > I1-I2.
          11
          > string:to_integer("0.5").
          {0,".5"}
          > string:to_integer("x=2").
          {error,no_integer}</code>
      </desc>
    </func>
    <func>
      <name name="to_lower" arity="1" clause_i="1"/>
      <name name="to_lower" arity="1" clause_i="2"/>
      <name name="to_upper" arity="1" clause_i="1"/>
      <name name="to_upper" arity="1" clause_i="2"/>
      <fsummary>Convert case of string (ISO/IEC 8859-1)</fsummary>
      <type variable="String" name_i="1"/>
      <type variable="Result" name_i="1"/>
      <type variable="Char"/>
      <type variable="CharResult"/>
      <desc>
        <p>The given string or character is case-converted. Note that
          the supported character set is ISO/IEC 8859-1 (a.k.a. Latin 1),
          all values outside this set is unchanged</p>
      </desc>
    </func>
  </funcs>

  <section>
    <title>Notes</title>
    <p>Some of the general string functions may seem to overlap each
      other. The reason for this is that this string package is the
      combination of two earlier packages and all the functions of
      both packages have been retained.
      </p>
    <note>
      <p>Any undocumented functions in <c>string</c> should not be used.</p>
    </note>
  </section>
</erlref>