Access struct elements in a class linitalizer list

Question

I'm working on an embedded-system project using EFM32GG11 series micro-controller. In project I've to read data from multiple serial port, process the data and forward the data to server via Ethernet.

I've created a class that will handle serial port. Multiple object of this class will be created.

I've created a constructor with initialize list. I've a question: Is their a way to directly access structure member in initialization list? - uart_init.baudRate(baud_rate)

class SerialPort {
public :
    enum PortList{
        COM1,   //RS-232
        COM2    //RS-232 -- 8 more ports
    };
private:
    PortList                                    port_no;
    UARTDRV_Init_t                              uart_init;
    uint32_t                                    baud_rate;
    char                                        parity;
    uint8_t                                     stop_bit;
    bool                                        single_line_mode;
    uint16_t                                    block_time; //in milli-seconds
public:
    SerialPort(PortList port_no, uint16_t baud_rate, char parity, uint8_t stop_bit,
        bool single_line_mode, uint16_t block_time) : port_no(port_no), uart_init.baudRate(baud_rate), parity(parity), stop_bit(stop_bit), single_line_mode(single_line_mode),
                block_time(block_time)
    {
          //Further processing post initialization
    }


};

UARTDRV_Init_t Strurcture:

typedef struct {
  USART_TypeDef              *port;             ///< The peripheral used for UART
  uint32_t                   baudRate;          ///< UART baud rate
} UARTDRV_InitUart_t;

Answer 1

You can use designated initializers (since C++20) to specify the member to be initialized. Eg

SerialPort(PortList port_no, uint16_t baud_rate, char parity, uint8_t stop_bit,
    bool single_line_mode, uint16_t block_time) : port_no(port_no), uart_init {.baudRate=baud_rate}, parity(parity), stop_bit(stop_bit), single_line_mode(single_line_mode),
//                                                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
            block_time(block_time)
{
      //Further processing post initialization
}

Before C++17, we can only initialize the data member itself in member initializer list and can't specify its subobject further more.

Answer 2

If you know the what the default for port should be, you could do it this way, assuming port is initialized to nullptr or something:

SerialPort(PortList port_no, uint16_t baud_rate, char parity, uint8_t stop_bit,
    bool single_line_mode, uint16_t block_time) : port_no(port_no), uart_init {nullptr, baud_rate}, parity(parity), stop_bit(stop_bit), single_line_mode(single_line_mode),
            block_time(block_time)
{
      ...
}