RegOpenKeyExA function (winreg.h)

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

LSTATUS RegOpenKeyExA(
  [in]           HKEY   hKey,
  [in, optional] LPCSTR lpSubKey,
  [in]           DWORD  ulOptions,
  [in]           REGSAM samDesired,
  [out]          PHKEY  phkResult
);

Parameters

[in] hKey

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

[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

Specifies the option to apply when opening the key. Set this parameter to zero or the following:

[in] samDesired

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.

[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.

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

lResult = RegOpenKeyEx (hKeyRoot, lpSubKey, 0, KEY_READ, &hKey);

if (lResult != ERROR_SUCCESS) 
{
    if (lResult == ERROR_FILE_NOT_FOUND) {
        printf("Key not found.\n");
        return TRUE;
    } 
    else {
        printf("Error opening key.\n");
        return FALSE;
    }
}

To see this example in context, see Deleting a Key with Subkeys.

Requirements

See also

RegCloseKey

RegCreateKeyEx

RegDeleteKey

RegOpenKeyTransacted

Registry Functions

Registry Overview