Article ID: 135398 - Last Review: February 2, 2005 - Revision: 3.4

How to write to the Windows registry by using Windows API calls

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This article was previously published under Q135398

SUMMARY

You can write information directly to the Microsoft Windows 95, Windows NT, or Win32 registry. The Windows registry is the suggested place for 32-bit applications to store application information. Previous versions of Windows used .INI files for this purpose. This article gives a brief description of the Windows registry and the steps necessary to write information to it programatically.

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MORE INFORMATION

The following information comes from Chapter 10 of the Windows NT Resource Kit:

The registry is analogous to the .INI files used under Windows 3.1, with each key in the registry similar to a bracketed heading in an .INI file, and entries under the heading similar to values in the registry. However, registry keys can contain subkeys, while .INI files do not support nested headings. Registry values can also consist of executable code, rather than the simple strings representing values in .INI files. And individual preferences for multiple users of the same computer can be stored in the registry, which is not possible with .INI files.

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Windows NT registry

The registry is a database of keys and values. The Windows NT registry contains four primary keys:

HKEY_CLASSES_ROOT   - File associations and DDE/OLE actions.

HKEY_LOCAL_MACHINE  - Global information on the state of the local
                      computer.

HKEY_USERS          - Configuration information about each individual user
                      of the computer and the DEFAULT entry.

HKEY_CURRENT_USER   - specific key within HKEY_USERS that stores
                      information for the currently active user.

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Windows 95 registry

Windows 95 adds a couple more primary keys:

HKEY_CURRENT_CONFIG - Hardware configuration for devices currently attached
                      and installed on the computer.

HKEY_DYN_DATA       - System Monitor data for performance settings and
                      statistics.

It is good idea for applications to store version specific information in the HKEY_LOCAL_MACHINE\SOFTWARE branch in this format:

   SOFTWARE\Vendor\product\version

The example code in this article shows one way to register an application name and version.

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Win32s registry

The Win32s registry is limited to only one hive, HKEY_CLASSES_ROOT, and all keys are children of that hive. Any information placed in the Win32s registry should be placed in a child key of HKEY_CLASSES_ROOT instead of HKEY_CLASSES_ROOT (used in Windows 95 and Windows NT).

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Sample code

The following code illustrate the ability to create a new registry key by using the Windows API RegCreateKeyEx() and to assign a value to that key by using RegSetValueEx. These 32bit functions are first prototyped using the DECLARE command; then they are available to be called directly. For more information, search for DECLARE - DLL in the Help menu.

Note Some constants are declared with definitions taken from the appropriate Microsoft Visual C++ header files.

* REGISTRY.PRG
* This code writes information to the HKEY_LOCAL_MACHINE\SOFTWARE key.
* It creates a key called MYAPPS, and a value name called AppName that
* contains the value "SuperApp 1.0"

PUBLIC RESULT,DISPLAY
RESULT=0
DISPLAY=0
#DEFINE HKEY_LOCAL_MACHINE 2147483650   && (HKEY) 0x80000002
#DEFINE SECURITY_ACCESS_MASK 983103     && SAM value KEY_ALL_ACCESS

DECLARE RegCreateKeyEx IN ADVAPI32.DLL;
INTEGER,STRING,INTEGER,STRING,INTEGER,INTEGER,INTEGER,INTEGER @, INTEGER @
DECLARE RegSetValueEx IN ADVAPI32.DLL;
INTEGER,STRING,INTEGER,INTEGER,STRING,INTEGER

?RegCreateKeyEx(HKEY_LOCAL_MACHINE,"SOFTWARE\MYAPPS",0,"REG_SZ",;
0,SECURITY_ACCESS_MASK,0,@RESULT,@DISPLAY)  && Returns .T. if successful
?RESULT                                     && Returns the key handle
?DISPLAY                                    && Returns one of 2 values:
                                            && REG_CREATE_NEW_KEY = 1
                                            && REG_OPENED_EXISTING_KEY = 2
?RegSetValueEx(RESULT,"AppName",0,1,"SuperApp 1.0",13)

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Notes

You can run the Registry Editor to see the registry interface and check that your key was created successfully in the HKEY_LOCAL_MACHINE\SOFTWARE section. In Windows NT, you can find it in the Winnt\System32\regedt32.exe directory. In Windows 95, you can find it in the Win95\Regedit.exe directory.

For more information, see the Win32API Help file that is uncluded with Visual FoxPro. Search for RegCreateKeyEx() and RegSetValueEx() as well as the Reg.h and Winnt.h header files to find some of the constant definitions used in the code. To remove these values, you can use the RegDeleteKey() and RegDeleteValue() functions.

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