You can always be explicit: #if WE_ARE_ON_A_TINY_MACHINE typedef uint16_t vector_size_t; #elif WE_ARE_ON_A_SUPERCOMPUTER typedef uint64_t vecto

You can always be explicit: #if WE_ARE_ON_A_TINY_MACHINE typedef uint16_t vector_size_t; #elif WE_ARE_ON_A_SUPERCOMPUTER typedef uint64_t vector_size_t; #else #error "Unsupported platform." #end That's better than your code which inserts 100,000 things into a vector mysteriously breaking on certain platforms (on which you may or may not have tested your code).