用C ++读取原始字节数据

Question

I have a really basic question. I want to turn an LED on/off depending on the BLE data received by a Nrf52 BLE device. My problem is that the data (Received_Data) is in raw bytes data form (1 byte), and I don't know how to perform an if statement on that, or convert it into a form that can. In the code below I have:

                if (Received_Data > 50)
                    {
                      nrf_gpio_pin_toggle(LED_2);
                    }
                 end

How can I let 'Received_Data' be used in an IF statement like this, so it can be read as an integer or a hex number?

        case APP_UART_DATA_READY:
        UNUSED_VARIABLE(app_uart_get(&data_array[index]));
        index++;

        if ((data_array[index - 1] == '\n') ||
            (data_array[index - 1] == '\r') ||
            (index >= m_ble_nus_max_data_len))
        {
            if (index > 1)
            {
                NRF_LOG_DEBUG("Ready to send data over BLE NUS");
                NRF_LOG_HEXDUMP_DEBUG(Received_Data, index);

                 if (Received_Data > 50)
                    {
                      nrf_gpio_pin_toggle(LED_2);
                    }
                 end

This is doing my head in. I'm sure this can be answered by someone in 5 seconds. and I am beyond the point where I can invest the time to dig through all the associated C++ documentation to find the solution.

Answer 1

Since Received_Data is an uint8_t array, you can access individual bytes directly:

if (Received_Data[0] > 50)
//or
if (Received_Data[index] > 50)

uint8_t is [0..255].

Answer 2

From your question

How can I let 'Received_Data' be used in an IF statement like this, so it can be read as an integer or a hex number?

From your comments

It is already defined as a uint8: uint8_t Received_Data[BLE_NUS_MAX_DATA_LEN];

Just want to check that the byte within the array is above or below a certain threshold, such as 50. What would be the syntax to do that with an IF statement?

Received_Data is an array of unsigned 8-bit integers. In the first piece of code you provided:

if (Received_Data > 50){
    nrf_gpio_pin_toggle(LED_2);
}

Received_Data decays to a pointer to the first element of the array. Therefore, you are actually comparing between a pointer and an integer (which is expressly forbidden by ISO C++). If you want to check the value of a specific element of that array, then you need to index it with the subscript operator like so:

//byte_of_interest is some non-negative integer value that specifically represents
//the element in the array that you are interested in comparing with 50
if (Received_Data[byte_of_interest] > 50){
    nrf_gpio_pin_toggle(LED_2);
}

Likewise, you can also use pointer arithmetic:

//byte_of_interest is an offset from the beginning of the array
//so its contents are located at the address to the beginning of the array + the offset
if (*(Received_Data + byte_of_interest) > 50){
    nrf_gpio_pin_toggle(LED_2);
}

Furthermore, I recommend that you initialize the array to 0 to prevent getting false positives before the array is filled in (eg uint8_t Received_Data[BLE_NUS_MAX_DATA_LEN] = {0}; )