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<erlref>
  <header>
    <copyright>
      <year>2000</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>win32reg</title>
    <prepared>Bjorn Gustavsson</prepared>
    <responsible>NN</responsible>
    <docno></docno>
    <approved>nobody</approved>
    <checked>no</checked>
    <date>2000-08-10</date>
    <rev>PA1</rev>
    <file>win32reg.sgml</file>
  </header>
  <module>win32reg</module>
  <modulesummary>win32reg provides access to the registry on Windows</modulesummary>
  <description>
    <p><c>win32reg</c> 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 is available in Windows 95 and
      Windows NT. 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 sub-keys to the right and backslash
      between keys. (Remember that backslashes must be doubled in Erlang strings.)
      Case is preserved but not significant.
      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 the <c>win32reg</c> module as:</p>
    <pre>
Abbrev.          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 could be written as <c>"\\hklm\\software\\ericsson\\erlang\\5.0"</c>.</p>
    <p>The <c>win32reg</c> module uses a current key. It works much like the
      current directory. From the current key, values can be fetched, sub-keys
      can be listed, and so on.</p>
    <p>Under a key, any number of named values can be stored. They have name, and
      types, and data.</p>
    <p>Currently, the <c>win32reg</c> module supports storing only the following
      types: REG_DWORD, which is an
      integer, REG_SZ which is a string and REG_BINARY which is a binary.
      Other types can be read, and will be 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,
      e.g. <c>"%SystemRoot%Windows"</c>. <c>SystemRoot</c> is an environment variable, and should be
      replaced with its value. A function <c>expand/1</c> is provided, so that environment
      variables surrounded in % can be expanded to their values.</p>
    <p>For additional information on the Windows registry consult the Win32
      Programmer's Reference.</p>
  </description>
  <datatypes>
    <datatype>
      <name name="reg_handle"/>
      <desc><p>As returned by <seealso marker="#open/1">open/1</seealso>.</p></desc>
    </datatype>
    <datatype>
      <name name="name"/>
    </datatype>
    <datatype>
      <name name="value"/>
    </datatype>
  </datatypes>
  <funcs>
    <func>
      <name name="change_key" arity="2"/>
      <fsummary>Move to a key in the registry</fsummary>
      <desc>
        <p>Changes the current key to another key. Works like cd.
          The key can be specified as a relative path or as an
          absolute path, starting with \.</p>
      </desc>
    </func>
    <func>
      <name name="change_key_create" arity="2"/>
      <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"/>
      <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"/>
      <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>Note that the current key is stored in the driver, and might be
          invalid (e.g. if the key has been removed).</p>
      </desc>
    </func>
    <func>
      <name name="delete_key" arity="1"/>
      <fsummary>Delete the current key</fsummary>
      <desc>
        <p>Deletes the current key, if it is valid. Calls the Win32 API
          function <c>RegDeleteKey()</c>. Note that this call does not change the current key,
          (unlike <c>change_key_create/2</c>.) This means that after the call, the
          current key is invalid.</p>
      </desc>
    </func>
    <func>
      <name name="delete_value" arity="2"/>
      <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 the default value.</p>
        <p>The registry must have been opened in write-mode.</p>
      </desc>
    </func>
    <func>
      <name name="expand" arity="1"/>
      <fsummary>Expand a string with environment variables</fsummary>
      <desc>
        <p>Expands a string containing environment variables between percent
          characters. Anything between two % is taken for a environment
          variable, and is replaced by the value. Two consecutive % is replaced
          by one %.</p>
        <p>A variable name that is not in the environment, will result in an error.</p>
      </desc>
    </func>
    <func>
      <name name="format_error" arity="1"/>
      <fsummary>Convert an POSIX errorcode to a string</fsummary>
      <desc>
        <p>Convert an POSIX errorcode to a string (by calling <c>erl_posix_msg:message</c>).</p>
      </desc>
    </func>
    <func>
      <name name="open" arity="1"/>
      <fsummary>Open the registry for reading or writing</fsummary>
      <desc>
        <p>Opens the registry for reading or writing. The current key will be the root
          (<c>HKEY_CLASSES_ROOT</c>). The <c>read</c> flag in the mode list can be omitted.</p>
        <p>Use <c>change_key/2</c> with an absolute path after <c>open</c>.</p>
      </desc>
    </func>
    <func>
      <name name="set_value" arity="3"/>
      <fsummary>Set value at the current registry key with specified name.</fsummary>
      <desc>
        <p>Sets the named (or default) value to value. Calls the Win32
          API function <c>RegSetValueEx()</c>. The value can be of three types, and
          the corresponding registry type will be used. Currently the types supported
          are: <c>REG_DWORD</c> for integers, <c>REG_SZ</c> for strings and
          <c>REG_BINARY</c> for binaries. Other types cannot currently 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"/>
      <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, it can be slow.</p>
      </desc>
    </func>
    <func>
      <name name="value" arity="2"/>
      <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"/>
      <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 <c>value</c>.
          Calls the Win32 API function <c>EnumRegValuesEx()</c>.</p>
      </desc>
    </func>
  </funcs>

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

