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

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <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
      limitations under the License.
    
    </legalnotice>

    <title>string</title>
    <prepared>Robert Virding</prepared>
    <responsible>Bjarne D&auml;cker</responsible>
    <docno>1</docno>
    <approved>Bjarne D&auml;cker</approved>
    <checked></checked>
    <date>1996-09-28</date>
    <rev>A</rev>
    <file>string.xml</file>
  </header>
  <module>string</module>
  <modulesummary>String processing functions.</modulesummary>
  <description>
    <p>This module provides functions for string processing.</p>
  </description>

  <funcs>
    <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 centered in the
          string and surrounded by blanks or <c><anno>Character</anno></c>.
	  The resulting string has length <c><anno>Number</anno></c>.</p>
      </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> characters
          <c><anno>Character</anno></c>. Optionally, the string can end with
          string <c><anno>Tail</anno></c>.</p>
      </desc>
    </func>

    <func>
      <name name="chr" arity="2"/>
      <fsummary>Return the index of the first occurrence of
        a character in a string.</fsummary>
      <desc>
        <p>Returns the index of the first occurrence of
          <c><anno>Character</anno></c> in <c><anno>String</anno></c>. Returns
          <c>0</c> if <c><anno>Character</anno></c> does not occur.</p>
      </desc>
    </func>

    <func>
      <name name="concat" arity="2"/>
      <fsummary>Concatenate two strings.</fsummary>
      <desc>
        <p>Concatenates <c><anno>String1</anno></c> and
          <c><anno>String2</anno></c> to form a new string
          <c><anno>String3</anno></c>, which is returned.</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="cspan" arity="2"/>
      <fsummary>Span characters at start of a string.</fsummary>
      <desc>
        <p>Returns the length of the maximum initial segment of
          <c><anno>String</anno></c>, which consists entirely of characters
          not from <c><anno>Chars</anno></c>.</p>
        <p><em>Example:</em></p>
        <code type="none">
> string:cspan("\t    abcdef", " \t").
0</code>
      </desc>
    </func>

    <func>
      <name name="equal" arity="2"/>
      <fsummary>Test string equality.</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>String1</anno></c> and
          <c><anno>String2</anno></c> are equal, otherwise <c>false</c>.</p>
      </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><em>Example:</em></p>
        <code type="none">
> join(["one", "two", "three"], ", ").
"one, two, three"</code>
      </desc>
    </func>

    <func>
      <name name="left" arity="2"/>
      <name name="left" arity="3"/>
      <fsummary>Adjust left end of a string.</fsummary>
      <desc>
        <p>Returns <c><anno>String</anno></c> with the length adjusted in
          accordance with <c><anno>Number</anno></c>. The left margin is
          fixed. If <c>length(<anno>String</anno>)</c> &lt;
          <c><anno>Number</anno></c>, then <c><anno>String</anno></c> is padded
          with blanks or <c><anno>Character</anno></c>s.</p>
        <p><em>Example:</em></p>
        <code type="none">
> string:left("Hello",10,$.).
"Hello....."</code>
      </desc>
    </func>

    <func>
      <name name="len" arity="1"/>
      <fsummary>Return the length of a string.</fsummary>
      <desc>
        <p>Returns the number of characters in <c><anno>String</anno></c>.</p>
      </desc>
    </func>

    <func>
      <name name="rchr" arity="2"/>
      <fsummary>Return the index of the last occurrence of
        a character in a string.</fsummary>
      <desc>
        <p>Returns the index of the last occurrence of
          <c><anno>Character</anno></c> in <c><anno>String</anno></c>. Returns
          <c>0</c> if <c><anno>Character</anno></c> does not occur.</p>
      </desc>
    </func>

    <func>
      <name name="right" arity="2"/>
      <name name="right" arity="3"/>
      <fsummary>Adjust right end of a string.</fsummary>
      <desc>
        <p>Returns <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>, then <c><anno>String</anno></c> is padded
          with blanks or <c><anno>Character</anno></c>s.</p>
        <p><em>Example:</em></p>
        <code type="none">
> string:right("Hello", 10, $.).
".....Hello"</code>
      </desc>
    </func>

    <func>
      <name name="rstr" arity="2"/>
      <fsummary>Find the index of a substring.</fsummary>
      <desc>
        <p>Returns the position where the last occurrence of
          <c><anno>SubString</anno></c> begins in <c><anno>String</anno></c>.
          Returns <c>0</c> if <c><anno>SubString</anno></c>
          does not exist in <c><anno>String</anno></c>.</p>
        <p><em>Example:</em></p>
        <code type="none">
> string:rstr(" Hello Hello World World ", "Hello World").
8</code>
      </desc>
    </func>

    <func>
      <name name="span" arity="2"/>
      <fsummary>Span characters at start of a string.</fsummary>
      <desc>
        <p>Returns the length of the maximum initial segment of
          <c><anno>String</anno></c>, which consists entirely of characters
          from <c><anno>Chars</anno></c>.</p>
        <p><em>Example:</em></p>
        <code type="none">
> string:span("\t    abcdef", " \t").
5</code>
      </desc>
    </func>

    <func>
      <name name="str" arity="2"/>
      <fsummary>Find the index of a substring.</fsummary>
      <desc>
        <p>Returns the position where the first occurrence of
          <c><anno>SubString</anno></c> begins in <c><anno>String</anno></c>.
          Returns <c>0</c> if <c><anno>SubString</anno></c>
          does not exist in <c><anno>String</anno></c>.</p>
        <p><em>Example:</em></p>
        <code type="none">
> string:str(" Hello Hello World World ", "Hello World").
8</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>, which can be <c>left</c>, <c>right</c>,
          or <c>both</c>, indicates from which direction blanks are to be
          removed. <c>strip/1</c> is equivalent to
          <c>strip(String, both)</c>.</p>
        <p><em>Example:</em></p>
        <code type="none">
> string:strip("...Hello.....", both, $.).
"Hello"</code>
      </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
          position <c><anno>Start</anno></c> to the end of the string, or to
          and including position <c><anno>Stop</anno></c>.</p>
        <p><em>Example:</em></p>
        <code type="none">
sub_string("Hello World", 4, 8).
"lo Wo"</code>
      </desc>
    </func>

    <func>
      <name name="substr" arity="2"/>
      <name name="substr" arity="3"/>
      <fsummary>Return a substring of a string.</fsummary>
      <desc>
        <p>Returns a substring of <c><anno>String</anno></c>, starting at
          position <c><anno>Start</anno></c>, and ending at the end of the
          string or at length <c><anno>Length</anno></c>.</p>
        <p><em>Example:</em></p>
        <code type="none">
> substr("Hello World", 4, 5).
"lo Wo"</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><em>Example:</em></p>
        <code type="none">
> string:sub_word(" Hello old boy !",3,$o).
"ld b"</code>
      </desc>
    </func>

    <func>
      <name name="to_float" arity="1"/>
      <fsummary>Returns a float whose text representation is the integers
        (ASCII values) in a string.</fsummary>
      <desc>
        <p>Argument <c><anno>String</anno></c> is expected to start with a
          valid text represented float (the digits are ASCII values).
          Remaining characters in the string after the float are returned in
          <c><anno>Rest</anno></c>.</p>
        <p><em>Example:</em></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 a string.</fsummary>
      <desc>
        <p>Argument <c><anno>String</anno></c> is expected to start with a
          valid text represented integer (the digits are ASCII values).
          Remaining characters in the string after the integer are returned in
          <c><anno>Rest</anno></c>.</p>
        <p><em>Example:</em></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 specified string or character is case-converted. Notice that
          the supported character set is ISO/IEC 8859-1 (also called Latin 1);
          all values outside this set are unchanged</p>
      </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><em>Example:</em></p>
        <code type="none">
> tokens("abc defxxghix jkl", "x ").
["abc", "def", "ghi", "jkl"]</code>
        <p>Notice that, as shown in this example, two or more
          adjacent separator characters in <c><anno>String</anno></c>
          are treated as one. That is, there are no empty
          strings in the resulting list of tokens.</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><em>Example:</em></p>
        <code type="none">
> words(" Hello old boy!", $o).
4</code>
      </desc>
    </func>
  </funcs>

  <section>
    <title>Notes</title>
    <p>Some of the general string functions can seem to overlap each
      other. The reason is that this string package is the
      combination of two earlier packages and all functions of
      both packages have been retained.</p>

    <note>
      <p>Any undocumented functions in <c>string</c> are not to be used.</p>
    </note>
  </section>
</erlref>