> On systems where 0 is a valid memory address the compiler should pick some other address that is not valid.
Not necessarily. Null dereference is undefined behavior so it may as well access some valid memory.
Even on platforms where 0 is a valid address, practical compilers tend to use 0 as null constant because it simplifies implementation (easy to check for null, matches the C syntax without WTFs).
This comes at the cost of making some small part of memory unusable to portable C code (nobody will believe you when you return 0 from malloc if 0 happens to be considered null), but that's fine because such memory is typically used for machine-specific, nonportable stuff anyway.
Not necessarily. Null dereference is undefined behavior so it may as well access some valid memory.
Even on platforms where 0 is a valid address, practical compilers tend to use 0 as null constant because it simplifies implementation (easy to check for null, matches the C syntax without WTFs).
This comes at the cost of making some small part of memory unusable to portable C code (nobody will believe you when you return 0 from malloc if 0 happens to be considered null), but that's fine because such memory is typically used for machine-specific, nonportable stuff anyway.