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Overview |
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Group |
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Quick Info
Windows NT
| Yes
| Win95
| Yes
| Win32s
| Yes
| Import Library
| advapi32.lib
| Header File
| winreg.h
| Unicode
| WinNT
| Platform Notes
| None
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RegQueryValueEx
The RegQueryValueEx function retrieves the type and data for a specified value name associated
with an open registry key.
LONG RegQueryValueEx(
HKEY hKey,
| // handle of key to query
| LPTSTR lpValueName,
| // address of name of value to query
| LPDWORD lpReserved,
| // reserved
| LPDWORD lpType,
| // address of buffer for value type
| LPBYTE lpData,
| // address of data buffer
| LPDWORD lpcbData
| // address of data buffer size
| );
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Parameters
hKey
Identifies a currently open key or any of the following predefined reserved
handle values:
HKEY_CLASSES_ROOT
HKEY_CURRENT_USER
HKEY_LOCAL_MACHINE
HKEY_USERS
lpValueName
Points to a null-terminated string containing the name of the value to be
queried.
lpReserved
Reserved; must be NULL.
lpType
Points to a variable that receives the key's value type. The value returned
through this parameter will be one of the following:
Value
| Meaning
| REG_BINARY
| Binary data in any form.
| REG_DWORD
| A 32-bit number.
| REG_DWORD_LITTLE_ENDIAN
| A 32-bit number in little-endian format (same as REG_DWORD). In little-endian
format, the most significant byte of a word is the high-order byte. This is the
most common format for computers running Windows NT and Windows 95.
| REG_DWORD_BIG_ENDIAN
| A 32-bit number in big-endian format. In big-endian format, the most
significant byte of a word is the low-order byte.
| REG_EXPAND_SZ
| A null-terminated string that contains unexpanded references to environment
variables (for example, "%PATH%"). It will be a Unicode or ANSI string depending
on whether you use the Unicode or ANSI functions.
| REG_LINK
| A Unicode symbolic link.
| REG_MULTI_SZ
| An array of null-terminated strings, terminated by two null characters.
| REG_NONE
| No defined value type.
| REG_RESOURCE_LIST
| A device-driver resource list.
| REG_SZ
| A null-terminated string. It will be a Unicode or ANSI string depending on
whether you use the Unicode or ANSI functions.
|
The lpType parameter can be NULL if the type is not required.
lpData
Points to a buffer that receives the value's data. This parameter can be NULL
if the data is not required.
lpcbData
Points to a variable that specifies the size, in bytes, of the buffer pointed
to by the lpData parameter. When the function returns, this variable contains the size of the
data copied to lpData.
If the buffer specified by lpData parameter is not large enough to hold the data, the function returns the
value ERROR_MORE_DATA, and stores the required buffer size, in bytes, into the
variable pointed to by lpcbData.
If lpData is NULL, and lpcbData is non-NULL, the function returns ERROR_SUCCESS, and stores the size of the
data, in bytes, in the variable pointed to by lpcbData. This lets an application determine the best way to allocate a buffer for the
value key's data.
If the data has the REG_SZ, REG_MULTI_SZ or REG_EXPAND_SZ type, then lpData will also include the size of the terminating null character.
The lpcbData parameter can be NULL only if lpData is NULL.
Return Values
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
The key identified by hKey must have been opened with KEY_QUERY_VALUE access. To open the key, use the RegCreateKeyEx or RegOpenKeyEx function.
This function does not expand the environment-variable names in the value data
when the value type is REG_EXPAND_SZ. The ExpandEnvironmentStrings function can be used to expand the environment-variable names.
If the value data has the REG_SZ, REG_MULTI_SZ or REG_EXPAND_SZ type, and the
ANSI version of this function is used (either by explicitly calling RegQueryValueEx or by not defining Unicode before including the WINDOWS.H file), this
function converts the stored Unicode string to an ANSI string before copying it to the
buffer pointed to by lpData.
When calling the RegQueryValueEx function with hKey set to the HKEY_PERFORMANCE_DATA handle and a value string of a specified
object, the returned data structure sometimes has unrequested objects. Don't be
surprised; this is normal behavior. When calling the RegQueryValueEx function, you should always expect to walk the returned data structure to
look for the requested object.
See Also
ExpandEnvironmentStrings, RegCreateKeyEx, RegEnumKey, RegEnumKeyEx, RegEnumValue, RegOpenKeyEx, RegQueryInfoKey, RegQueryValue
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