The RegQueryValueEx function retrieves the type and data for a specified value name associated with an open registry key.
LONG RegQueryValueEx(
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HKEY hKey, |
// handle of key to query |
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LPTSTR lpValueName, |
// address of name of value to query |
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LPDWORD lpReserved, |
// reserved |
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LPDWORD lpType, |
// address of buffer for value type |
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LPBYTE lpData, |
// address of data buffer |
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LPDWORD lpcbData |
// address of data buffer size |
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); |
HKEY_CLASSES_ROOT
HKEY_CURRENT_CONFIG
HKEY_CURRENT_USER
HKEY_LOCAL_MACHINE
HKEY_USERS
Windows NT only: HKEY_PERFORMANCE_DATA
Windows 95 only: HKEY_DYN_DATA
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Value |
Meaning |
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REG_BINARY |
Binary data in any form. |
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REG_DWORD |
A 32-bit number. |
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REG_DWORD_LITTLE_ENDIAN |
A 32-bit number in little-endian format. This is equivalent to REG_DWORD. In little-endian format, a multi-byte value is stored in memory from the lowest byte (the “little end”) to the highest byte. For example, the value 0x12345678 is stored as (0x78 0x56 0x34 0x12) in little-endian format. Windows NT and Windows 95 are designed to run on little-endian computer architectures. A user may connect to computers that have big-endian architectures, such as some UNIX systems. |
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REG_DWORD_BIG_ENDIAN |
A 32-bit number in big-endian format. In big-endian format, a multi-byte value is stored in memory from the highest byte (the “big end”) to the lowest byte. For example, the value 0x12345678 is stored as (0x12 0x34 0x56 0x78) in big-endian format. |
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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. |
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REG_LINK |
A Unicode symbolic link. |
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REG_MULTI_SZ |
An array of null-terminated strings, terminated by two null characters. |
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REG_NONE |
No defined value type. |
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REG_RESOURCE_LIST |
A device-driver resource list. |
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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.
If the data has the REG_SZ, REG_MULTI_SZ or REG_EXPAND_SZ type, then lpcbData will also include the size of the terminating null character.
The lpcbData parameter can be NULL only if lpData is NULL.
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’s data.
Window NT: If hKey specifies HKEY_PERFORMANCE_DATA and the lpData buffer is too small, RegQueryValueEx returns ERROR_MORE_DATA but lpcbData does not return the required buffer size. This is because the size of the performance data can change from one call to the next. In this case, you must increase the buffer size and call RegQueryValueEx again passing the updated buffer size in the lpcbData parameter. Repeat this until the function succeeds.
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.
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 RegQueryValueExA 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.
Window NT: 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.
ExpandEnvironmentStrings, RegCreateKeyEx, RegEnumKey, RegEnumKeyEx, RegEnumValue, RegOpenKeyEx, RegQueryInfoKey, RegQueryValue