This sort of thing will likely cause more problems than it solves. Such a struct can't be moved, copied, or put in an array without potential memory corruption.

This sort of thing will likely cause more problems than it solves. Such a struct can't be moved, copied, or put in an array without potential memory corruption. I'd suggest doing this: typedef struct { int a; int b; /* private */ int c; int d; } STYPE; Sure, other programmers are free to ignore the comment and use the private fields anyway, but that suggests a bigger problem that can't be fixed with a clever pre-processor hack.