I really don't quite understand the reason for this cast

[Overworked_PhD]

#define BUFSIZE 1500

char sendbuf[BUFSIZE];

void send_v4(void)
{
     int len;
     stuct icmp *icmp;

     icmp = (struct icmp *) sendbuf;
     icmp->icmptype = ICMP_ECHO;
     icmp->icmpcode = 0;

    /*rest of code*/
}

The question is why force a cast to the array sendbuf? Ie why not do something like

#define BUFSIZE 1500

char sendbuf[BUFSIZE];

void send_v4(void)
{
     int len;
     stuct icmp *icmp;

     icmp->icmptype = ICMP_ECHO;
     icmp->icmpcode = 0;

    /*rest of code*/
}

I'm just sort of curious because this type of coding move appears in ping and a lot of unix network printer code.

[whiteflags]

Well one reason that whatever you saw wasn't written the way you suggested is because they later dereference that icmp pointer, and you can't dereference a pointer with an undefined value.

For whatever reason the programmer wanted an array of bytes (or at least I assume, given that it is a character array) interpreted like an instance of struct icmp. I wouldn't be surprised if what you're reading works over a network because data is basically sent over in packets like sendbuff.

If you're trying to learn how to network, I'm not sure if reading the code for your ping application is a good teacher.

[matsp]

Well one reason that whatever you saw wasn't written the way you suggested is because they later dereference that icmp pointer, and you can't dereference a pointer with an undefined value.

Sure you CAN do that - it just won't give a good result, as it'd "undefined behaviour" and "anything can happen" - most likely, it's going to crash.

--
Mats

[whiteflags]

And specifically that's why you can't. There is no reason not to forbid undefined behavior in the first place.