GetFirmwareEnvironmentVariableEx function

Retrieves the value of the specified firmware environment variable and its attributes.

Syntax

BOOL WINBASEAPI GetFirmwareEnvironmentVariableEx(
   LPCSTR lpName,
   LPCSTR lpGuid,
   PVOID  pValue,
   DWORD  nSize,
   PDWORD pdwAttributes
);

Parameters

lpName

The name of the firmware environment variable. The pointer must not be NULL.

lpGuid

The GUID that represents the namespace of the firmware environment variable. The GUID must be a string in the format "{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}" where 'x' represents a hexadecimal value. The pointer must not be NULL.

pValue

A pointer to a buffer that receives the value of the specified firmware environment variable.

nSize

The size of the pValue buffer, in bytes.

pdwAttributes

Bitmask identifying UEFI variable attributes associated with the variable. See SetFirmwareEnvironmentVariableEx for the bitmask definition.

Return value

If the function succeeds, the return value is the number of bytes stored in the pValue buffer.

If the function fails, the return value is zero. To get extended error information, call GetLastError. Possible error codes include ERROR_INVALID_FUNCTION.

Remarks

The exact set of firmware environment variables is determined by the boot firmware. The location of these environment variables is also specified by the firmware. For example, on a UEFI-based system, NVRAM contains firmware environment variables that specify system boot settings. For information about specific variables used, see the UEFI specification. For more information about UEFI and Windows, see UEFI and Windows.

Firmware variables are not supported on a legacy BIOS-based system. The GetFirmwareEnvironmentVariableEx function will always fail on a legacy BIOS-based system, or if Windows was installed using legacy BIOS on a system that supports both legacy BIOS and UEFI. To identify these conditions, call the function with a dummy firmware environment name such as an empty string ("") for the lpName parameter and a dummy GUID such as "{00000000-0000-0000-0000-000000000000}" for the lpGuid parameter. On a legacy BIOS-based system, or on a system that supports both legacy BIOS and UEFI where Windows was installed using legacy BIOS, the function will fail with ERROR_INVALID_FUNCTION. On a UEFI-based system, the function will fail with an error specific to the firmware, such as ERROR_NOACCESS, to indicate that the dummy GUID namespace does not exist.

If you are creating a backup application, you can use this function to save all the boot settings for the system so they can be restored using the SetFirmwareEnvironmentVariable function if needed.

Requirements

See also

SetFirmwareEnvironmentVariableEx

GetFirmwareEnvironmentVariable