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  <header>
    <copyright>
      <year>2000</year><year>2020</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>win32reg</title>
    <prepared>Bjorn Gustavsson</prepared>
    <responsible></responsible>
    <docno></docno>
    <approved></approved>
    <checked></checked>
    <date>2000-08-10</date>
    <rev>PA1</rev>
    <file>win32reg.xml</file>
  </header>
  <module since="">win32reg</module>
  <modulesummary>Provides access to the registry on Windows.</modulesummary>
  <description>
    <p>This module provides read and write access to the
      registry on Windows. It is essentially a port driver wrapped around the
      Win32 API calls for accessing the registry.</p>
    <p>The registry is a hierarchical database, used to store various system
      and software information in Windows.
      It contains installation data, and is updated by installers
      and system programs. The Erlang installer updates the registry by adding
      data that Erlang needs.</p>
    <p>The registry contains keys and values. Keys are like the directories
      in a file system, they form a hierarchy. Values are like files, they have
      a name and a value, and also a type.</p>
    <p>Paths to keys are left to right, with subkeys to the right and backslash
      between keys. (Remember that backslashes must be doubled in Erlang
      strings.) Case is preserved but not significant.</p>
    <p>For example,
      <c>"\\hkey_local_machine\\software\\Ericsson\\Erlang\\5.0"</c> is the key
      for the installation data for the latest Erlang release.</p>
    <p>There are six entry points in the Windows registry, top-level keys.
      They can be abbreviated in this module as follows:</p>
    <pre>
Abbreviation     Registry key
============     ============
hkcr             HKEY_CLASSES_ROOT
current_user     HKEY_CURRENT_USER
hkcu             HKEY_CURRENT_USER
local_machine    HKEY_LOCAL_MACHINE
hklm             HKEY_LOCAL_MACHINE
users            HKEY_USERS
hku              HKEY_USERS
current_config   HKEY_CURRENT_CONFIG
hkcc             HKEY_CURRENT_CONFIG
dyn_data         HKEY_DYN_DATA
hkdd             HKEY_DYN_DATA</pre>
    <p>The key above can be written as
      <c>"\\hklm\\software\\ericsson\\erlang\\5.0"</c>.</p>
    <p>This module uses a current key. It works much like the
      current directory. From the current key, values can be fetched, subkeys
      can be listed, and so on.</p>
    <p>Under a key, any number of named values can be stored. They have names,
      types, and data.</p>
    <p><c>win32reg</c> supports storing of the following types:</p>
    <list type="bulleted">
      <item><c>REG_DWORD</c>, which is an integer</item>
      <item><c>REG_SZ</c>, which is a string</item>
      <item><c>REG_BINARY</c>, which is a binary</item>
    </list>
    <p>Other types can be read, and are returned as binaries.</p>
    <p>There is also a "default" value, which has the empty string as name. It
      is read and written with the atom <c>default</c> instead of the name.</p>
    <p>Some registry values are stored as strings with references to environment
      variables, for example, <c>%SystemRoot%Windows</c>. <c>SystemRoot</c> is
      an environment variable, and is to be replaced with its value. Function
      <seemfa marker="#expand/1"><c>expand/1</c></seemfa> is provided so that
      environment variables surrounded by <c>%</c> can be expanded to their
      values.</p>
    <p>For more information on the Windows registry, see consult the Win32
      Programmer's Reference.</p>
  </description>

  <datatypes>
    <datatype>
      <name name="reg_handle"/>
      <desc>
        <p>As returned by
          <seemfa marker="#open/1"><c>open/1</c></seemfa>.</p>
      </desc>
    </datatype>
    <datatype>
      <name name="name"/>
    </datatype>
    <datatype>
      <name name="value"/>
    </datatype>
  </datatypes>

  <funcs>
    <func>
      <name name="change_key" arity="2" since=""/>
      <fsummary>Move to a key in the registry.</fsummary>
      <desc>
        <p>Changes the current key to another key. Works like <c>cd</c>.
          The key can be specified as a relative path or as an
          absolute path, starting with <c>\.</c></p>
      </desc>
    </func>

    <func>
      <name name="change_key_create" arity="2" since=""/>
      <fsummary>Move to a key, create it if it is not there.</fsummary>
      <desc>
        <p>Creates a key, or just changes to it, if it is already there. Works
          like a combination of <c>mkdir</c> and <c>cd</c>.
          Calls the Win32 API function <c>RegCreateKeyEx()</c>.</p>
        <p>The registry must have been opened in write mode.</p>
      </desc>
    </func>

    <func>
      <name name="close" arity="1" since=""/>
      <fsummary>Close the registry.</fsummary>
      <desc>
        <p>Closes the registry. After that, the <c><anno>RegHandle</anno></c>
          cannot be used.</p>
      </desc>
    </func>

    <func>
      <name name="current_key" arity="1" since=""/>
      <fsummary>Return the path to the current key.</fsummary>
      <desc>
        <p>Returns the path to the current key. This is the equivalent of
          <c>pwd</c>.</p>
        <p>Notice that the current key is stored in the driver, and can be
          invalid (for example, if the key has been removed).</p>
      </desc>
    </func>

    <func>
      <name name="delete_key" arity="1" since=""/>
      <fsummary>Delete the current key.</fsummary>
      <desc>
        <p>Deletes the current key, if it is valid. Calls the Win32 API
          function <c>RegDeleteKey()</c>. Notice that this call does not change
	  the current key (unlike
          <seemfa marker="#change_key_create/2">
          <c>change_key_create/2</c></seemfa>).
          This means that after the call, the current key is invalid.</p>
      </desc>
    </func>

    <func>
      <name name="delete_value" arity="2" since=""/>
      <fsummary>Delete the named value on the current key.</fsummary>
      <desc>
        <p>Deletes a named value on the current key. The atom <c>default</c> is
          used for the default value.</p>
        <p>The registry must have been opened in write mode.</p>
      </desc>
    </func>

    <func>
      <name name="expand" arity="1" since=""/>
      <fsummary>Expand a string with environment variables.</fsummary>
      <desc>
        <p>Expands a string containing environment variables between percent
          characters. Anything between two <c>%</c> is taken for an environment
          variable, and is replaced by the value. Two consecutive <c>%</c> are
          replaced by one <c>%</c>.</p>
        <p>A variable name that is not in the environment results in an
          error.</p>
      </desc>
    </func>

    <func>
      <name name="format_error" arity="1" since=""/>
      <fsummary>Convert a POSIX error code to a string.</fsummary>
      <desc>
        <p>Converts a POSIX error code to a string
	(by calling <c>erl_posix_msg:message/1</c>).</p>
      </desc>
    </func>

    <func>
      <name name="open" arity="1" since=""/>
      <fsummary>Open the registry for reading or writing.</fsummary>
      <desc>
        <p>Opens the registry for reading or writing. The current key is the
          root (<c>HKEY_CLASSES_ROOT</c>). Flag <c>read</c> in the mode list
          can be omitted.</p>
        <p>Use <seemfa marker="#change_key/2"><c>change_key/2</c></seemfa>
          with an absolute path after
          <seemfa marker="#open/1"><c>open</c></seemfa>.</p>
      </desc>
    </func>

    <func>
      <name name="set_value" arity="3" since=""/>
      <fsummary>Set value at the current registry key with specified name.
      </fsummary>
      <desc>
        <p>Sets the named (or default) value to <c>value</c>. Calls the Win32
          API function <c>RegSetValueEx()</c>. The value can be of three types,
          and the corresponding registry type is used. The supported types
          are the following:</p>
        <list type="bulleted">
          <item><c>REG_DWORD</c> for integers</item>
          <item><c>REG_SZ</c> for strings</item>
          <item><c>REG_BINARY</c> for binaries</item>
        </list>
        <p>Other types cannot be added or changed.</p>
        <p>The registry must have been opened in write mode.</p>
      </desc>
    </func>

    <func>
      <name name="sub_keys" arity="1" since=""/>
      <fsummary>Get subkeys to the current key.</fsummary>
      <desc>
        <p>Returns a list of subkeys to the current key. Calls the Win32
          API function <c>EnumRegKeysEx()</c>.</p>
        <p>Avoid calling this on the root keys, as it can be slow.</p>
      </desc>
    </func>

    <func>
      <name name="value" arity="2" since=""/>
      <fsummary>Get the named value on the current key.</fsummary>
      <desc>
        <p>Retrieves the named value (or default) on the current key.
          Registry values of type <c>REG_SZ</c> are returned as strings.
	  Type <c>REG_DWORD</c> values are returned as integers. All other
	  types are returned as binaries.</p>
      </desc>
    </func>

    <func>
      <name name="values" arity="1" since=""/>
      <fsummary>Get all values on the current key.</fsummary>
      <desc>
        <p>Retrieves a list of all values on the current key. The values
          have types corresponding to the registry types, see
	  <seemfa marker="#value/2"><c>value/2</c></seemfa>.
          Calls the Win32 API function <c>EnumRegValuesEx()</c>.</p>
      </desc>
    </func>
  </funcs>

  <section>
    <title>See Also</title>
    <p><c>erl_posix_msg</c>,
      The Windows 95 Registry (book from O'Reilly),
      Win32 Programmer's Reference (from Microsoft)</p>
  </section>
</erlref>

