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parentheses in defining a pointer C programming

I am a newbie in C progrmming and I have looked at the following code:

struct iphdr *iph = (struct iphdr *)Buffer;

What does the expression mean?

here is the link to the code http://www.binarytides.com/packet-sniffer-code-c-linux/

Solution

  • It casts buffer to a pointer to struct iphdr and then initializes iph to that pointer. This is used because buffer is a pointer to a buffer of raw bytes, but in this function it is known that the bytes stored in the buffer follow the format of a struct iphdr. Hence the struct iphdr can be used to access the contents of the buffer, rather than having to interpret and manipulate the raw bytes.

    edit: To clarify (as per comments): The cast does not copy or convert anything. It is basically just telling the compiler “I know that buffer is supposed to contain unsigned chars but at this particular time those bytes are actually a struct iphdr so let me access them through the pointer iph in a more convenient way”.