[Win32 API] RegQueryInfoKey

RegQueryInfoKey Function

Retrieves information about the specified registry key.

LONG WINAPI RegQueryInfoKey(
  __in          HKEY hKey,
  __out         LPTSTR lpClass,
  __in_out      LPDWORD lpcClass,
  LPDWORD lpReserved,
  __out         LPDWORD lpcSubKeys,
  __out         LPDWORD lpcMaxSubKeyLen,
  __out         LPDWORD lpcMaxClassLen,
  __out         LPDWORD lpcValues,
  __out         LPDWORD lpcMaxValueNameLen,
  __out         LPDWORD lpcMaxValueLen,
  __out         LPDWORD lpcbSecurityDescriptor,
  __out         PFILETIME lpftLastWriteTime
);

Parameters

hKey

A handle to an open registry key. The key must have been opened with the KEY_QUERY_VALUE 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

Windows Me/98/95:  This parameter can also be the following key:

HKEY_DYN_DATA

lpClass

A pointer to a buffer that receives the key class. This parameter can be NULL.

lpcClass

A pointer to a variable that specifies the size of the buffer pointed to by the lpClass parameter, in characters.

The size should include the terminating null character. When the function returns, this variable contains the size of the class string that is stored in the buffer. The count returned does not include the terminating null character. If the buffer is not big enough, the function returns ERROR_MORE_DATA, and the variable contains the size of the string, in characters, without counting the terminating null character.

If lpClass is NULL, lpcClass can be NULL.

If the lpClass parameter is a valid address, but the lpcClass parameter is not, for example, it is NULL, then the function returns ERROR_INVALID_PARAMETER.

Windows Me/98/95:  If the lpClass parameter is a valid address, but the lpcClass parameter is not, for example, it is NULL, then the function returns ERROR_SUCCESS instead of ERROR_INVALID_PARAMETER. To ensure compatibility with other platforms, verify that lpcClass is valid before calling the function.

lpReserved

This parameter is reserved and must be NULL.

lpcSubKeys

A pointer to a variable that receives the number of subkeys that are contained by the specified key. This parameter can be NULL.

lpcMaxSubKeyLen

A pointer to a variable that receives the size of the key's subkey with the longest name, in Unicode characters, not including the terminating null character. This parameter can be NULL.

Windows Me/98/95:  The size includes the terminating null character.

lpcMaxClassLen

A pointer to a variable that receives the size of the longest string that specifies a subkey class, in Unicode characters. The count returned does not include the terminating null character. This parameter can be NULL.

lpcValues

A pointer to a variable that receives the number of values that are associated with the key. This parameter can be NULL.

lpcMaxValueNameLen

A pointer to a variable that receives the size of the key's longest value name, in Unicode characters. The size does not include the terminating null character. This parameter can be NULL.

lpcMaxValueLen

A pointer to a variable that receives the size of the longest data component among the key's values, in bytes. This parameter can be NULL.

lpcbSecurityDescriptor

A pointer to a variable that receives the size of the key's security descriptor, in bytes. This parameter can be NULL.

lpftLastWriteTime

A pointer to a FILETIME structure that receives the last write time. This parameter can be NULL.

The function sets the members of the FILETIME structure to indicate the last time that the key or any of its value entries is modified.

Windows Me/98/95:  The function sets the members of the FILETIME structure to 0 (zero), because the system does not keep track of registry key last write time information.

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 the lpClass buffer is too small to receive the name of the class, the function returns ERROR_MORE_DATA.

Example Code

For an example, see Enumerating Registry Subkeys.

Requirements

Client	Requires Windows Vista, Windows XP, Windows 2000 Professional, Windows NT Workstation, Windows Me, Windows 98, or Windows 95.
Server	Requires Windows Server 2008, Windows Server 2003, Windows 2000 Server, or Windows NT Server.
Header	Declared in Winreg.h; include Windows.h.
Library	Use Advapi32.lib.
DLL	Requires Advapi32.dll.
Unicode	Implemented as RegQueryInfoKeyW (Unicode) and RegQueryInfoKeyA (ANSI).