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<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">
<erlref>
<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
<seealso marker="#expand/1"><c>expand/1</c></seealso> 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
<seealso marker="#open/1"><c>open/1</c></seealso>.</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
<seealso marker="#change_key_create/2">
<c>change_key_create/2</c></seealso>).
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 <seealso marker="#change_key/2"><c>change_key/2</c></seealso>
with an absolute path after
<seealso marker="#open/1"><c>open</c></seealso>.</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
<seealso marker="#value/2"><c>value/2</c></seealso>.
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>
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