Thread: Casting Question (I think)

Sorry for the obscure title.

I assume this is casting (i hope)

Code:

struct ip_header *ip
 
ip = (struct ip_header *) (packet + ethernetHeader)

Assuming i am correct, this next bit of code threw me.

Funtion pcap_next retruns a u_char pointer to the packet it captures.

I thought the code would be:

Code:

u_char *packet
packet = pcap_next(exp1, exp2)

However in the book i have its written:

Code:

u_char packet*
packet = (u_char *) pcap_next(exp1, exp2)

Is this casting?? Was my original understanding of casting incorrect, it not a subject im very familiar about.

Just having trouble understanding why the code in the book (which is correct) has the (u_char) before pcap_next.

Many thanks for any help!

Thankyou for the reply!

I see what you mean, just wanted to make sure i has understood casts!! Was looking at bitwise operators yesterday too, all fun!

Mind me asking about the malloc comment?

My understanding of malloc was that it returned a void pointer type, just assigns the memory to the type structure.

Thus:

char a
a = 5

could you do:

char a*
malloc(size of a)

So you have allocated the space in memory to put your data before you place the data in that space?

Just curious how casting and malloc were related??

Anyway, thanks for the reply, appreciate it!

could you do:

char a*
malloc(size of a)

Close. What you would actually do is:

Code:

char *a; /* Create a pointer to a char.  Name this pointer 'a' */
a = malloc(sizeof(*a)); /* allocate memory to store 1 char.  Assign 'a' to this allocated memory */

I see! cool.

Dont know why i missed the '='!

Cheers.

wow, thats quite complicated! Cheers tho, very interesting!