For cross platform interoperability, API with the exact size type helps remove any ambiguity. Using size_t might be fine for intra-process usage, but as soon as we are dealing with data across platforms, exact size type definition is a must.
I see it the other way around. How many bits you need to address something in memory depends on the platform. Thus `size_t` is the only cross-platform type you can use. A fixed-size integral is going to work on some, but not all.
That is correct. For file formats and packets etc you must use exact sizes.
However for cross platform support using size_t in an API (as in what is exposed via .dll or .so) is a must. It's exactly the correct way to write cross platform code.
