BluetoothGATTGetCharacteristics function

The BluetoothGATTGetCharacteristics function gets all the characteristics available for the specified service.

Syntax


HRESULT WINAPI BluetoothGATTGetCharacteristics(
  _In_       HANDLE hDevice,
  _In_opt_   PBTH_LE_GATT_SERVICE Service,
  _In_       USHORT CharacteristicsBufferCount,
  _Out_opt_  PBTH_LE_GATT_CHARACTERISTIC CharacteristicsBuffer,
  _Out_      USHORT* CharacteristicsBufferActual,
  _In_       ULONG Flags
);

Parameters

hDevice [in]

Handle to the Bluetooth device or service.

Service [in, optional]

The parent service of the included services to be retrieved. This parameter is required if a device handle is passed to hDevice. This parameter is optional if a service handle was passed to hDevice, in which case the service specified by the service handle will be treated as the parent.

CharacteristicsBufferCount [in]

The number of elements allocated for the CharacteristicsBuffer parameter.

CharacteristicsBuffer [out, optional]

Pointer to buffer into which to return characteristics.

CharacteristicsBufferActual [out]

Pointer to buffer into which the actual number of characteristics were returned in the CharacteristicsBuffer parameter.

Flags [in]

Flags to modify the behavior of BluetoothGATTGetCharacteristics:

FlagDescription

BLUETOOTH_GATT_FLAG_NONE

The client does not have specific GATT requirements (default).

 

Return value

This function returns the following values:

Return codeDescription
S_OK

The operation completed successfully.

ERROR_MORE_DATA

The buffer parameter is NULL and the number of items available is being returned instead.

ERROR_ACCESS_DENIED

Returned if both a parent service and a service handle are provided and the service hierarchy does not roll up to the provided parent service handle.

ERROR_INVALID_PARAMETER

One of the following conditions occurred:

  • CharacteristicsBuffer is NULL, and CharacteristicsBufferCount is 0
  • CharacteristicsBuffer is non-NULL, but CharacteristicsBufferCount is NULL
  • CharacteristicsBuffer is non-NULL, and CharacteristicsBufferCount is 0
ERROR_INVALID_USER_BUFFER

A buffer is specified, but the buffer count size is smaller than what is required, in bytes.

ERROR_BAD_COMMAND

The current data in the cache appears to be inconsistent, and is leading to internal errors.

ERROR_NO_SYSTEM_RESOURCES

The operation ran out of memory.

 

Remarks

Returned characteristics are cached upon successful retrieval of characteristics from the device directly. Unless a service-change event is received, the list of returned characteristics is not expected to change.

Profile drivers should pre-allocate a sufficiently large buffer for the array of characteristcs to be returned in. Callers can determine the necessary buffer size by passing a non-NULL value in CharacteristicsBufferActual and NULL in CharacteristicsBuffer.

Do not modify the returned characteristic structure, and then use the modified structure in subsequent function calls. Behavior is undefined if the caller does this.

The parent service must be present in the cache, otherwise the function will fail. The parent service must be a service returned by either BluetoothGATTGetServices or BluetoothGATTGetIncludedServices.

Example



////////////////////////////////////////////////////////////////////////////
// Determine Characteristic Buffer Size
////////////////////////////////////////////////////////////////////////////

        hr = BluetoothGATTGetCharacteristics(
                hCurrService,
                currGattService,
                0,
                NULL,
                &charBufferSize,
                BLUETOOTH_GATT_FLAG_NONE);
        
        if (HRESULT_FROM_WIN32(ERROR_MORE_DATA) != hr) {
            PrintHr("BluetoothGATTGetCharacteristics - Buffer Size", hr);
            goto Done;
        }
        
        if (charBufferSize > 0) {
            pCharBuffer = (PBTH_LE_GATT_CHARACTERISTIC)
                    malloc(charBufferSize * sizeof(BTH_LE_GATT_CHARACTERISTIC));
        
            if (NULL == pCharBuffer) {
                printf("pCharBuffer out of memory\r\n");
                goto Done;
            } else {
                RtlZeroMemory(pCharBuffer, 
                        charBufferSize * sizeof(BTH_LE_GATT_CHARACTERISTIC));
            }

////////////////////////////////////////////////////////////////////////////
// Retrieve Characteristics
////////////////////////////////////////////////////////////////////////////
    
            hr = BluetoothGATTGetCharacteristics(
                    hCurrService,
                    currGattService,
                    charBufferSize,
                    pCharBuffer,
                    &numChars,
                    BLUETOOTH_GATT_FLAG_NONE);

            if (S_OK != hr) {
                PrintHr("BluetoothGATTGetCharacteristics - Actual Data", hr);
                goto Done; // Allow continuation
            }

            if (numChars != charBufferSize) {
                printf("buffer size and buffer size actual size mismatch\r\n");
                goto Done;
            }
        }


Requirements

Version

Supported in Windows 8 and later versions of Windows.

Header

Bluetoothleapis.h

Library

BluetoothApis.lib

See also

BTH_LE_GATT_SERVICE
BTH_LE_GATT_CHARACTERISTIC

 

 

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