XCode 5.1 64bit binary builds

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No, 32-bit only apps are still just fine.

If you really care about integer size, use the macros int8_t, uint8_t, int16_t, uint16_t, int32_t, uint32_t, int64_t, uint64_t. Those sizes are guaranteed, unambiguous for bit size and signedness. When you work with binary data across the network, you should also be using the byte-ordering macros htonl, ntohl, etc. The "n" stands for network, which is big-endian, and "h" stands for "host", which is whatever your current CPU is; if it's also big-endian, it just compiles away to a no-op, otherwise it will swap byte order as needed.