Question

I was trying to figure out a piece of code which constructs a hostent object, more specifically, the part of it’s work that populates the h_addr_list array.

I was confused by the fact that the values that were assigned into the array were cast to char*, seeing as this array has nothing to do with strings as far as I read.

I noticed that the h_addr_list array is actually typed as char**.

The only place I saw that takes note of this fact is section 9.7 in beej’s Guide to Network Programming, but even there there’s no explanation on why is it typed so.

Is there a reason that h_addr_list is typed as char** and not void*/void** (or anything else that might be a bit more informative)?

Answer 1

char * needn’t necessarily refer to a C string, but also to a chunk of memory of known length that needs to be addressed by byte, presumably because it arrives from the network.

Before types like int8_t and uint8_t were added to C99, char * was the only practical way to refer to a contiguous byte array. In fact, struct hostent predates C89 which formalized the void type. If written today, the field would be declared as void ** or possibly uint8_t **.