WdfRegistryQueryUnicodeString function (wdfregistry.h)

Article
04/18/2022

[Applies to KMDF and UMDF]

The WdfRegistryQueryUnicodeString method retrieves the string data that is currently assigned to a specified registry string value and copies the string to a specified UNICODE_STRING structure.

Syntax

NTSTATUS WdfRegistryQueryUnicodeString(
  [in]            WDFKEY           Key,
  [in]            PCUNICODE_STRING ValueName,
  [out, optional] PUSHORT          ValueByteLength,
  [in, out]       PUNICODE_STRING  Value
);

Parameters

[in] Key

A handle to a registry-key object that represents an opened registry key.

[in] ValueName

A pointer to a UNICODE_STRING structure that contains a name for the registry value.

[out, optional] ValueByteLength

A pointer to a location that receives the number of bytes that are contained in the Unicode string that Value points to, including the terminating NULL byte. This pointer is optional and can be NULL

[in, out] Value

A pointer to a UNICODE_STRING structure that receives the data string for the key that Key specifies. If this parameter is NULL and ValueByteLength is non-NULL, WdfRegistryQueryUnicodeString returns only the size of the string.

Return value

WdfRegistryQueryUnicodeString returns STATUS_SUCCESS if the operation succeeds. Otherwise, the method might return one of the following values:

Return code	Description
STATUS_INVALID_DEVICE_REQUEST	WdfRegistryQueryUnicodeString was not called at IRQL = PASSIVE_LEVEL.
STATUS_INVALID_PARAMETER	An invalid parameter was specified.
STATUS_INSUFFICIENT_RESOURCES	There was insufficient memory to complete the operation.
STATUS_ACCESS_DENIED	The driver did not open the registry key with KEY_QUERY_VALUE, KEY_READ, or KEY_ALL_ACCESS access.
STATUS_OBJECT_TYPE_MISMATCH	The data type of the registry value that the ValueName parameter specified was not REG_SZ.
STATUS_BUFFER_OVERFLOW	The buffer that the Value parameter points to was too small, and only partial data was written to the buffer.
STATUS_BUFFER_OVERFLOW	The buffer that the Value parameter points to was too small, and no data was written to the buffer.
STATUS_OBJECT_NAME_NOT_FOUND	The registry value was not available.

This method also might return other NTSTATUS values.

A bug check occurs if the driver supplies an invalid object handle.

Remarks

For more information about registry-key objects, see Using the Registry in Framework-Based Drivers.

Examples

The following code example, which is from the Serial sample driver, retrieves the Unicode string that represents the string data that is assigned to the PortName value under a device's hardware key.

NTSTATUS
SerialReadSymName(
    IN WDFDEVICE Device,
    __out PWCHAR RegName,
    IN OUT PUSHORT LengthOfRegName // In characters
    )
{
    NTSTATUS status;
    WDFKEY hKey;
    UNICODE_STRING value;
    UNICODE_STRING valueName;
    USHORT requiredLength;

    value.Buffer = RegName;
    value.MaximumLength = *LengthOfRegName;
    value.Length = 0;

    status = WdfDeviceOpenRegistryKey(
                                      Device,
                                      PLUGPLAY_REGKEY_DEVICE,
                                      STANDARD_RIGHTS_ALL,
                                      WDF_NO_OBJECT_ATTRIBUTES,
                                      &hKey
                                      );

    if (NT_SUCCESS (status)) {
        RtlInitUnicodeString(
                             &valueName,
                             L"PortName"
                             );
        status = WdfRegistryQueryUnicodeString (
                                      hKey,
                                      &valueName,
                                      &requiredLength,
                                      &value
                                      );
        WdfRegistryClose(hKey);
    }
    return status;
}

Requirements

Requirement	Value
Target Platform	Universal
Minimum KMDF version	1.0
Minimum UMDF version	2.0
Header	wdfregistry.h (include Wdf.h)
Library	Wdf01000.sys (KMDF); WUDFx02000.dll (UMDF)
IRQL	PASSIVE_LEVEL
DDI compliance rules	DriverCreate(kmdf), KmdfIrql(kmdf), KmdfIrql2(kmdf), KmdfIrqlExplicit(kmdf)

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