Question

I am trying to make a structure for a data packet that has a dynamic payload length and is determined by a variable within the header struct (LEN).

I am unsure on how to do this properly and I am confused by some of the examples that i have come across. Bellow is the Structure that is the basis of what i will be using.
Thanks.

struct packet
{
    unsigned char payload;
    unsigned int CRC : 16;

    struct header
    {
        unsigned char SRC;
        unsigned char DST;
        unsigned char NS : 3;       //3 bits long
        unsigned char NR : 3;
        unsigned char RSV : 1;      //1 bit long
        unsigned char LST : 1;
        unsigned char OP;
        unsigned char LEN;
    } HEADER;

};

struct packet PACKET;

Answer 1

Make the payload a pointer instead and allocate it at runtime according to the value of LEN in the header field.