RegEnumKeyExA function (winreg.h)

Article
03/11/2023

Enumerates the subkeys of the specified open registry key. The function retrieves information about one subkey each time it is called.

Syntax

LSTATUS RegEnumKeyExA(
  [in]                HKEY      hKey,
  [in]                DWORD     dwIndex,
  [out]               LPSTR     lpName,
  [in, out]           LPDWORD   lpcchName,
                      LPDWORD   lpReserved,
  [in, out]           LPSTR     lpClass,
  [in, out, optional] LPDWORD   lpcchClass,
  [out, optional]     PFILETIME lpftLastWriteTime
);

Parameters

[in] hKey

A handle to an open registry key. The key must have been opened with the KEY_ENUMERATE_SUB_KEYS access right. For more information, see Registry Key Security and Access Rights.

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

HKEY_CLASSES_ROOT

HKEY_CURRENT_CONFIG

HKEY_CURRENT_USER

HKEY_LOCAL_MACHINE

HKEY_PERFORMANCE_DATA

HKEY_USERS

[in] dwIndex

The index of the subkey to retrieve. This parameter should be zero for the first call to the RegEnumKeyEx function and then incremented for subsequent calls.

Because subkeys are not ordered, any new subkey will have an arbitrary index. This means that the function may return subkeys in any order.

[out] lpName

A pointer to a buffer that receives the name of the subkey, including the terminating null character. The function copies only the name of the subkey, not the full key hierarchy, to the buffer.

If the function fails, no information is copied to this buffer.

For more information, see Registry Element Size Limits.

[in, out] lpcchName

A pointer to a variable that specifies the size of the buffer specified by the lpName parameter, in characters. This size should include the terminating null character. If the function succeeds, the variable pointed to by lpcchName contains the number of characters stored in the buffer, not including the terminating null character.

To determine the required buffer size, use the RegQueryInfoKey function to determine the size of the largest subkey for the key identified by the hKey parameter.

lpReserved

This parameter is reserved and must be NULL.

[in, out] lpClass

A pointer to a buffer that receives the user-defined class of the enumerated subkey. This parameter can be NULL.

[in, out, optional] lpcchClass

A pointer to a variable that specifies the size of the buffer specified by the lpClass parameter, in characters. The size should include the terminating null character. If the function succeeds, lpcchClass contains the number of characters stored in the buffer, not including the terminating null character. This parameter can be NULL only if lpClass is NULL.

[out, optional] lpftLastWriteTime

A pointer to FILETIME structure that receives the time at which the enumerated subkey was last written. This parameter can be NULL.

Return value

If the function succeeds, the return value is ERROR_SUCCESS.

If the function fails, the return value is a system error code. If there are no more subkeys available, the function returns ERROR_NO_MORE_ITEMS.

If the lpName buffer is too small to receive the name of the key, the function returns ERROR_MORE_DATA.

Remarks

To enumerate subkeys, an application should initially call the RegEnumKeyEx function with the dwIndex parameter set to zero. The application should then increment the dwIndex parameter and call RegEnumKeyEx until there are no more subkeys (meaning the function returns ERROR_NO_MORE_ITEMS).

The application can also set dwIndex to the index of the last subkey on the first call to the function and decrement the index until the subkey with the index 0 is enumerated. To retrieve the index of the last subkey, use the RegQueryInfoKey function.

While an application is using the RegEnumKeyEx function, it should not make calls to any registration functions that might change the key being enumerated.

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.

Note

On legacy versions of Windows, this API is also exposed by kernel32.dll.

Examples

For an example, see Enumerating Registry Subkeys.

Note

The winreg.h header defines RegEnumKeyEx 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.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	winreg.h (include Windows.h)
Library	Advapi32.lib
DLL	Advapi32.dll

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