When should you use a class vs a struct in C++?

Question

In what scenarios is it better to use a struct vs a class in C++?

Answer 1

One place where a struct has been helpful for me is when I have a system that's receiving fixed format messages (over say, a serial port) from another system. You can cast the stream of bytes into a struct that defines your fields, and then easily access the fields.

typedef struct
{
    int messageId;
    int messageCounter;
    int messageData;
} tMessageType;

void processMessage(unsigned char *rawMessage)
{
    tMessageType *messageFields = (tMessageType *)rawMessage;
    printf("MessageId is %d\n", messageFields->messageId);
}

Obviously, this is the same thing you would do in C, but I find that the overhead of having to decode the message into a class is usually not worth it.