RegOpenKeyTransactedA function (winreg.h)

Opens the specified registry key and associates it with a transaction. Note that key names are not case sensitive.


LSTATUS RegOpenKeyTransactedA(
  [in]           HKEY   hKey,
  [in, optional] LPCSTR lpSubKey,
  [in]           DWORD  ulOptions,
  [in]           REGSAM samDesired,
  [out]          PHKEY  phkResult,
  [in]           HANDLE hTransaction,
                 PVOID  pExtendedParemeter


[in] hKey

A handle to an open registry key. This handle is returned by the RegCreateKeyEx, RegCreateKeyTransacted, RegOpenKeyEx, or RegOpenKeyTransacted function. It can also be one of the following predefined keys:


[in, optional] lpSubKey

The name of the registry subkey to be opened.

Key names are not case sensitive.

If the lpSubKey parameter is NULL or a pointer to an empty string, and if hKey is a predefined key, then the system refreshes the predefined key, and phkResult receives the same hKey handle passed into the function. Otherwise, phkResult receives a new handle to the opened key.

For more information, see Registry Element Size Limits.

[in] ulOptions

This parameter is reserved and must be zero.

[in] samDesired

A mask that specifies the desired access rights to the key. 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.

[out] phkResult

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.

[in] hTransaction

A handle to an active transaction. This handle is returned by the CreateTransaction function.


This parameter is reserved and must be NULL.

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.


When a key is opened using this function, subsequent operations on the key are transacted. If a non-transacted operation is performed on the key before the transaction is committed, the transaction is rolled back. After a transaction is committed or rolled back, you must re-open the key using the RegCreateKeyTransacted or RegOpenKeyTransacted function with an active transaction handle to make additional operations transacted. For more information about transactions, see Kernel Transaction Manager.

Note that subsequent operations on subkeys of this key are not automatically transacted. Therefore, the RegDeleteKeyEx function does not perform a transacted delete operation. Instead, use the RegDeleteKeyTransacted function to perform a transacted delete operation.

Unlike the RegCreateKeyTransacted function, the RegOpenKeyTransacted function does not create the specified key if the key does not exist in the registry.

If your service or application impersonates different users, do not use this function with HKEY_CURRENT_USER. Instead, call the RegOpenCurrentUser function.

If the key returned in phkResult is a predefined registry key, it is not included in the provided transaction.

A single registry key can be opened only 65,534 times. When attempting the 65,535th open operation, this function fails with ERROR_NO_SYSTEM_RESOURCES.


The winreg.h header defines RegOpenKeyTransacted as an alias which automatically selects the ANSI or Unicode version of this function based on the definition of the UNICODE preprocessor constant. Mixing usage of the encoding-neutral alias with code that not encoding-neutral can lead to mismatches that result in compilation or runtime errors. For more information, see Conventions for Function Prototypes.


Requirement Value
Minimum supported client Windows Vista [desktop apps only]
Minimum supported server Windows Server 2008 [desktop apps only]
Target Platform Windows
Header winreg.h (include Windows.h)
Library Advapi32.lib
DLL Advapi32.dll

See also




Registry Functions

Registry Overview