What's the "DNS_BLOCK_ASSERTIONS" (C compiler flag)?
The NS_BLOCK_ASSERTIONS macro (no "D") suppresses the checks performed by NSAssert. You supply it to the compiler using -DNS_BLOCK_ASSERTIONS (see the comments for an explanation of the "D").
来源：https://stackoverflow.com/questions/2752574/whats-the-dns-block-assertions-c-compiler-flag