Discover characteristics by UUID

This procedure is useful when the Client intends to discover a specific Characteristic in a specific Service. The API allows for multiple Characteristics of the same type to be discovered, but most often it is used when a single Characteristic of the given type is expected to be found.

Continuing the example from Discover primary services by UUID, assume the Client wants to discover the Heart Rate Control Point Characteristic inside the Heart Rate Service, as shown in the following code.

gattService_t * pService = &heartRateService;
**static **gattCharacteristic_t hrcpCharacteristic;
**static **uint8_t mcHrcpChar;
bleResult_t result = GattClient_DiscoverCharacteristicOfServiceByUuid
(
    deviceId,
    *gBleUuidType16\_c*,
    gBleSig_HrControlPoint_d,
    pService,
    &hrcpCharacteristic,
    1,
    &mcHrcpChar
);

This API can be used as in the previous examples, following a Service Discovery procedure. However, the user may want to perform a Characteristic search with UUID over the entire database, skipping the Service Discovery entirely. To do so, a dummy service structure must be defined and its range must be set to maximum, as shown in the following example:

gatt Service_t dummyService;
dummyService. startHandle = 0x0001;
dummyService. endHandle = 0xFFFF;
**static **gattCharacteristic_t hrcpCharacteristic;
**static **uint8_t mcHrcpChar;
bleResult_t result = **GattClient\_DiscoverCharacteristicOfServiceByUuid**
(
    deviceId,
    *gBleUuidType16\_c*,
    gBleSig_HrControlPoint_d,
    &dummyService,
    &hrcpCharacteristic,
    1,
    &mcHrcpChar
);

In either case, the value of the mcHrcpChar variable should be checked in the procedure callback.

**void ****gattClientProcedureCallback**
(
    deviceId_t             deviceId,
    gattProcedureType_t    procedureType,
    gattProcedureResult_t  procedureResult,
    bleResult_t            error
)
{
    **switch** (procedureType)
    {
        /* ... */
        **case***gGattProcDiscoverCharacteristicByUuid\_c*:
            **if** (*gGattProcSuccess\_c* == procedureResult)
            {
                **if** (1 == mcHrcpChar)
                {
                    /* HRCP found, read discovered data */
                    PRINT(hrcpCharacteristic. properties );
                    PRINT(hrcpCharacteristic. value . handle );
                }
                **else**
                {
                    /* HRCP not found! */
                }
            }
            **else**
            {
                /* Handle error */
                PRINT(error);
            }
            **break**;
        /* ... */
    }
}

Parent topic:Service and characteristic discovery