win32reg(3erl) Erlang Module Definition win32reg(3erl)
NAME
win32reg - win32reg provides access to the registry on Windows
DESCRIPTION
win32reg 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.
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.
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.
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: "\hkey_local_machine\software\Ericsson\Erlang\5.0" is the key for the
installation data for the latest Erlang release.
There are six entry points in the Windows registry, top level keys. They can be abbreviated in the win32reg module as:
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
The key above could be written as "\hklm\software\ericsson\erlang\5.0" .
The win32reg 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.
Under a key, any number of named values can be stored. They have name, and types, and data.
Currently, the win32reg 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.
There is also a "default" value, which has the empty string as name. It is read and written with the atom default instead of the name.
Some registry values are stored as strings with references to environment variables, e.g. "%SystemRoot%Windows" . SystemRoot is an environ-
ment variable, and should be replaced with its value. A function expand/1 is provided, so that environment variables surrounded in % can be
expanded to their values.
For additional information on the Windows registry consult the Win32 Programmer's Reference.
EXPORTS
change_key(RegHandle, Key) -> ReturnValue
Types RegHandle = term()
Key = string()
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 .
change_key_create(RegHandle, Key) -> ReturnValue
Types RegHandle = term()
Key = string()
Creates a key, or just changes to it, if it is already there. Works like a combination of mkdir and cd . Calls the Win32 API func-
tion RegCreateKeyEx() .
The registry must have been opened in write-mode.
close(RegHandle)-> ReturnValue
Types RegHandle = term()
Closes the registry. After that, the RegHandle cannot be used.
current_key(RegHandle) -> ReturnValue
Types RegHandle = term()
ReturnValue = {ok, string()}
Returns the path to the current key. This is the equivalent of pwd .
Note that the current key is stored in the driver, and might be invalid (e.g. if the key has been removed).
delete_key(RegHandle) -> ReturnValue
Types RegHandle = term()
ReturnValue = ok | {error, ErrorId}
Deletes the current key, if it is valid. Calls the Win32 API function RegDeleteKey() . Note that this call does not change the cur-
rent key, (unlike change_key_create/2 .) This means that after the call, the current key is invalid.
delete_value(RegHandle, Name) -> ReturnValue
Types RegHandle = term()
ReturnValue = ok | {error, ErrorId}
Deletes a named value on the current key. The atom default is used for the the default value.
The registry must have been opened in write-mode.
expand(String) -> ExpandedString
Types String = string()
ExpandedString = string()
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 %.
A variable name that is not in the environment, will result in an error.
format_error(ErrorId) -> ErrorString
Types ErrorId = atom()
ErrorString = string()
Convert an POSIX errorcode to a string (by calling erl_posix_msg:message ).
open(OpenModeList)-> ReturnValue
Types OpenModeList = [OpenMode]
OpenMode = read | write
Opens the registry for reading or writing. The current key will be the root ( HKEY_CLASSES_ROOT ). The read flag in the mode list
can be omitted.
Use change_key/2 with an absolute path after open .
set_value(RegHandle, Name, Value) -> ReturnValue
Types Name = string() | default
Value = string() | integer() | binary()
Sets the named (or default) value to value. Calls the Win32 API function RegSetValueEx() . The value can be of three types, and the
corresponding registry type will be used. Currently the types supported are: REG_DWORD for integers, REG_SZ for strings and
REG_BINARY for binaries. Other types cannot currently be added or changed.
The registry must have been opened in write-mode.
sub_keys(RegHandle) -> ReturnValue
Types ReturnValue = {ok, SubKeys} | {error, ErrorId}
SubKeys = [SubKey]
SubKey = string()
Returns a list of subkeys to the current key. Calls the Win32 API function EnumRegKeysEx() .
Avoid calling this on the root keys, it can be slow.
value(RegHandle, Name) -> ReturnValue
Types Name = string() | default
ReturnValue = {ok, Value}
Value = string() | integer() | binary()
Retrieves the named value (or default) on the current key. Registry values of type REG_SZ , are returned as strings. Type REG_DWORD
values are returned as integers. All other types are returned as binaries.
values(RegHandle) -> ReturnValue
Types ReturnValue = {ok, ValuePairs} | {ok, ErrorId}
ValuePairs = [ValuePair]
ValuePair = {Name, Value}
Name = string | default
Value = string() | integer() | binary()
Retrieves a list of all values on the current key. The values have types corresponding to the registry types, see value . Calls the
Win32 API function EnumRegValuesEx() .
SEE ALSO
Win32 Programmer's Reference (from Microsoft)
erl_posix_msg
The Windows 95 Registry (book from O'Reilly)
Ericsson AB stdlib 1.17.3 win32reg(3erl)