How using stdint.h has advantage of portability?

Question

I read that stdint.h is used for portability, but I'm confused.

If I wrote a program on a 32-bit system, uint32_t (unsigned int) is 4-bytes.

But when this program is run on 16-bit system, int is 2bytes and uint32_t (unsigned int) is 2bytes.

I think portability is not guaranteed in this case. Is there anything I am understanding wrong?

Answer 1

A uint32_t and a uint16_t are distinct types from int.

While the size of int may vary, a uint32_t is always 32 bit and a uint16_t is always 16 bit.

Answer 2

Is there any thing I am understanding wrong?

Yes.

Type uint32_t is always an unsigned integer type with exactly 32 bits, none of them padding bits. On many modern systems that corresponds to type unsigned int, but on others it might correspond to a different type, such as unsigned long int. On systems that do not have a type with the correct properties, it is not defined at all.

The point of uint32_t and the other explicit-width data types from stdint.h is exactly to address the issue you raise, that (for example) unsigned int has a different size on different machines.