RegOpenKeyEx function
Applies to: desktop apps only
Opens the specified registry key. Note that key names are not case sensitive.
To perform transacted registry operations on a key, call the RegOpenKeyTransacted function.
Syntax
LONG WINAPI RegOpenKeyEx( __in HKEY hKey, __in_opt LPCTSTR lpSubKey, __reserved DWORD ulOptions, __in REGSAM samDesired, __out PHKEY phkResult );
Parameters
- hKey [in]
-
A handle to an open registry key. This handle is returned by the RegCreateKeyEx or RegOpenKeyEx function, or it can be one of the following predefined keys:
- HKEY_CLASSES_ROOT
- HKEY_CURRENT_CONFIG
- HKEY_CURRENT_USER
- HKEY_LOCAL_MACHINE
- HKEY_USERS
- lpSubKey [in, optional]
-
The name of the registry subkey to be opened.
Key names are not case sensitive.
The lpSubKey parameter can be a pointer to an empty string. If lpSubKey is a pointer to an empty string and hKey is HKEY_CLASSES_ROOT, phkResult receives the same hKey handle passed into the function. Otherwise, phkResult receives a new handle to the key specified by hKey.
The lpSubKey parameter can be NULL only if hKey is one of the predefined keys. If lpSubKey is NULL and hKey is HKEY_CLASSES_ROOT, phkResult receives a new handle to the key specified by hKey. Otherwise, phkResult receives the same hKey handle passed in to the function.
For more information, see Registry Element Size Limits.
- ulOptions
-
This parameter is reserved and must be zero.
- samDesired [in]
-
A mask that specifies the desired access rights to the key to be opened. The function fails if the security descriptor of the key does not permit the requested access for the calling process. For more information, see Registry Key Security and Access Rights.
- phkResult [out]
-
A pointer to a variable that receives a handle to the opened key. If the key is not one of the predefined registry keys, call the RegCloseKey function after you have finished using the handle.
Return value
If the function succeeds, the return value is ERROR_SUCCESS.
If the function fails, the return value is a nonzero error code defined in Winerror.h. You can use the FormatMessage function with the FORMAT_MESSAGE_FROM_SYSTEM flag to get a generic description of the error.
Remarks
Unlike the RegCreateKeyEx function, the RegOpenKeyEx function does not create the specified key if the key does not exist in the registry.
Certain registry operations perform access checks against the security descriptor of the key, not the access mask specified when the handle to the key was obtained. For example, even if a key is opened with a samDesired of KEY_READ, it can be used to create registry keys if the key's security descriptor permits. In contrast, the RegSetValueEx function specifically requires that the key be opened with the KEY_SET_VALUE access right.
If your service or application impersonates different users, do not use this function with HKEY_CURRENT_USER. Instead, call the RegOpenCurrentUser function.
Note that operations that access certain registry keys are redirected. For more information, see Registry Virtualization and 32-bit and 64-bit Application Data in the Registry.
Examples
For an example, see Deleting a Key with Subkeys.
Requirements
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Minimum supported client | Windows 2000 Professional |
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Minimum supported server | Windows 2000 Server |
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Header |
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Library |
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DLL |
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Unicode and ANSI names | RegOpenKeyExW (Unicode) and RegOpenKeyExA (ANSI) |
See also
- RegCloseKey
- RegCreateKeyEx
- RegDeleteKey
- Registry Functions
- Registry Overview
- RegOpenKeyTransacted
- RegQueryKeyEx
Send comments about this topic to Microsoft
Build date: 3/6/2012
"samDesired [in]
A mask that specifies the desired access rights to the key to be opened. The function fails if the security descriptor of the key does not permit the requested access for the calling process. For more information, see Registry Key Security and Access Rights."
The function fails with FILE_NOT_FOUND when you don't add KEY_WOW64_32KEY and it's not very helpful when the key is visible in REGEDIT!
- 1/18/2012
- Warren Menzer
lpSubKey [in, optional]
The name of the registry subkey to be opened.
Key names are not case sensitive.
The lpSubKey parameter can be a pointer to an empty string. If lpSubKey is a pointer to an empty string and hKey is HKEY_CLASSES_ROOT, phkResult receives the same hKey handle passed into the function. Otherwise, phkResult receives a new handle to the key specified by hKey.
The lpSubKey parameter can be NULL only if hKey is one of the predefined keys. If lpSubKey is NULL and hKey is HKEY_CLASSES_ROOT, phkResult receives a new handle to the key specified by hKey. Otherwise, phkResult receives the same hKey handle passed in to the function.
</RegOpenKeyEx function (Windows) - Current Documentation>
<RegOpenKeyEx function (Windows) - My Proposed Revised Documentation>
lpSubKey [in, optional]
The name of the registry subkey to be opened.
Key names are not case sensitive.
The lpSubKey parameter can be a pointer to an empty string. If lpSubKey is a pointer to an empty string and hKey is one of the predefined keys, the contents of phkResult receives a handle back to the same predefined key specified by hKey which was passed into the function. Otherwise, for the case of a non-empty string, hReturn receives a new handle to the key specified by or corresponding to the lpSubKey string.
The lpSubKey parameter can be NULL. If the lpSubKey parameter is NULL, the contents of phkResult receives the same hKey handle passed into the function, predefined or not. For example. if pSubKey is NULL and hKey is HKEY_CLASSES_ROOT, one of the predefined keys, the contents of phkResult receives a handle back to the same predefined key specified by hKey which was passed into the function. Similarly, if lpSubKey is NULL and hKey is not a predefined key, the contents of phkResult receives the same hKey handle passed into the function.
If the lpSubKey parameter specified is not empty nor NULL, it must point to a subkey name of the key identified by the hKey parameter.
</RegOpenKeyEx function (Windows) - My Proposed Revised Documentation>
Question: What happens if you attempt to close a predefined registry key (ie. ::RegCloseKey(HKEY_CLASSES_ROOT)? -- Nothing? Throws an exception? There is no mention in the documentation of what happens in this case. If Microsoft prevents the closing of predefined keys, it would just make sense to close the key all the time. Microsoft would then worry about whether the key is predefined or not, and trap or block a predefined key from being closed.
- 10/12/2011
- jmsigler2 [Contractor-Consultant]
- 10/13/2011
- jmsigler2 [Contractor-Consultant]
- 10/4/2011
- jakub2
- 8/25/2011
- Jim Michaels
- 2/21/2007
- rhowen
- 7/29/2011
- rogerdpack2
Claimed: "If lpSubKey is NULL and hKey is HKEY_CLASSES_ROOT, phkResult receives a new handle to the key specified by hKey." Actual: ERROR_SUCCESS is returned and the output parameter pointed to by phkResult is HKEY_CLASSES_ROOT (80000000).
Tested this on Windows XP and Windows 7.
- 9/8/2010
- lordjeb
solution:
// ensure 16bit aligned string if unicode
#ifdef UNICODE
in_KeyPath = EnsureAlignedString(in_KeyPath, lv_PathBuf, 256);
#endif
// open subkey
if (RegOpenKeyEx(in_hBaseKey, in_KeyPath, 0, KEY_QUERY_VALUE, &lv_hKey) != 0)
return FALSE;
where:
TCHAR *EnsureAlignedString(TCHAR *in_Str, TCHAR *in_Buf, INT in_MaxLen)
{
// registry calls needs unicode strings to be aligned on 16bit boundaries
if ((INT)in_Str & 1)
{
// alignment is needed, copy to aligned buffer
tstrncpyeos(in_Buf, in_Str, in_MaxLen-1);
// use the buffer
return in_Buf;
}
else
{
// already aligned
return in_Str;
}
}
- 4/20/2010
- ArnoudMulder
lResult = RegOpenKeyEx (hKeyRoot, lpSubKey, 0, KEY_READ, &hKey);
But this one fails in Windows 2000
lResult = RegOpenKeyEx (hKeyRoot, lpSubKey, 0, KEY_READ|KEY_WOW64_32KEY, &hKey);
The difference? The KEY_WOW64_32KEY:
http://msdn.microsoft.com/en-us/library/ms724878%28VS.85%29.aspx
- 10/21/2009
- luxspes
- 9/15/2008
- DaveMethvin
- 11/29/2007
- Gideon7
