Advantages/Disadvantages of using __int16 (or int16_t) over int

Question

As far as I understand, the number of bytes used for int is system dependent. Usually, 2 or 4 bytes are used for int.

As per Microsoft's documentation, __int8, __int16, __int32 and __int64 are Microsoft Specific keywords. Furthermore, __int16 uses 16-bits (i.e. 2 bytes).

Question: What are advantage/disadvantage of using __int16 (or int16_t)? For example, if I am sure that the value of my integer variable will never need more than 16 bits then, will it be beneficial to declare the variable as __int16 var (or int16_t var)?

UPDATE: I see that several comments/answers suggest using int16_t instead of __int16, which is a good suggestion but not really an advantage/disadvantage of using __int16. Basically, my question is, what is the advantage/disadvantage of saving 2 bytes by using 16-bit version of an integer instead of int ?

Answer 1

Saving 2 bytes is almost never worth it. However, saving thousands of bytes is. If you have an large array containing integers, using a small integer type can save quite a lot of memory. This leads to faster code, because the less memory one uses the less cache misses one receives (cache misses are a major loss of performance).

TL;DR: this is beneficial to do in large arrays, but pointless for 1-off variables.

The second use of these is if for dealing with binary files and messages. If you are reading a binary file that uses 16-bit integers, well, it's pretty convenient if you can represent that type exactly in your code.

BTW, don't use microsoft's versions. Use the standard versions (std::int16_t)