A pointer to any type of a value will take up the full 64 bits in size in both languages. An Int in Swift will take up 64 bits or 8 bytes of storage. An int in C on a 64 bit system will ( typically) take up 32 bits or 4 bytes of storage. Note: Now’s as good as time as any to mention type sizes in a programming language. The -e option says to format the output in little-endian byte order (i.e. The -g 4 says to group all the values into 4 bytes, which is perfect since each member in the mach_header_64 struct is a 4 byte value. The xxd command will dump the raw data of an executable to stdout. Lolgrep:~ $ xxd -g 4 -e $(which grep ) | head -2 The mach_header_64 struct contains the following: The resolved filepath of loader.h can be viewed via: cat $(xcrun -show-sdk-path)/usr/include/mach-o/loader.h | less -R This resolves to the base directory search path for C system headers. Note: When referring to C System headers on your OS X machine, you can usually resolve the header location to the following Terminal command: echo $(xcrun -show-sdk-path)/usr/include. In the file, there exists a C struct called mach_header_64 that is the beginning to all 64-bit compiled Apple images (well, sorta, it actually depends on some things like FAT files, 32-bit architecture, but don’t think about that now).
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