Do I have to change param's type when migrating my lib to 64bit?

I am migrating my lib from 32bit to 64bit. The library is written in C. Say for the following API:

void foo(uint32 var)

Do I have to change the type of var to uint64 in any circumstances? What if max of var is not greater than 0xffffffff?

Do I have to change the type of var to uint64 in any circumstances? What if max of var is not greater than 0xffffffff?

Nothing says you have to change your datatypes when compiling for 64-bit. The uint32 parameter will behave the same as it did before. (However, you should probably be using uint32_t from <stdint.h> if you want to guarantee that your data types work correctly.)

There are a few other places where you want the size of your variables to change, but the behavior will be automatically correct if you use the correct data types:

• uintptr_t This is a pointer-sized integer. So you can cast from void* to uintptr_t and back without losing any information. If you instead cast from void* to uint32_t, you will corrupt your pointers.
• off_t The size of file offsets might change (depending on your toolchain), so you should use this appropriate typedef.