I have started to learn c++ for some time ago. It is a big subject and I am not
ID: 658615 • Letter: I
Question
I have started to learn c++ for some time ago. It is a big subject and I am not very use to it yet. Thus is this question asked more of curiosity, than something else. In the book that I read to now learn there is a discussion about portability. I agree that the discussion comes quite earky for someone in the beginning of their learning period, but when reading I came to Think about something.
What I wonder is: is there ever is a reason to define custom type to use instead of the fundamental builtin types? For example, would it be useful to define a type int_c as in "int custom"? The reason I think about this is since some code may be compiled for example both a 32-bit compiler and a 64-bit compiler. It seems as if it would be easier since if you change platform and all the integers are defined as int_c instead of int, since the latter would require changing type in every place an int is used?
However, I also know that <cstdint> contains definitions of different integer as int64_t. However I have not heard of a header with floating Point types.
So to conclude: Is there a reason to define custom integers or floats like int_c or double_c Or int other case what is the best apporach?
Explanation / Answer
There is sometimes a reason to do so, however <stdint.h> (in C99) or <cstdint> (in C++03 or beter) make them less obvious.
First, there is a readability issue. If you define
typedef unsigned myhash_t;
and later always use myhash_t for numbers which are in fact hashes, you ease the understanding of your code. This does not help much against your own mistakes (e.g. forgetting to declare a parameter as myhash_t even if it is an hash) but it does enhance readability.
Then with <stdint.h> (etc...) you have many new integral types (most of them being system-specific synonyms of e.g. int and long), like int64_t (a signed int of exactly 64 bits), uintptr_t (an unsigned integer with the same size as pointers), int_fast8t (an integral type, which is computed quickly, of at least 8 bits, but it could be 16 bits if they run faster, etc...)
At last, you may place preprocessor tricks with e.g. #if combined to such typedef-s. For instance, you could define a color encoding as having 3 RGB (or 4, RGBA) components of
typedef uint8_t color_t;
but some preprocessor trick might make that an uint16_t ....
FWIW, Ocaml and Ada are doing better than C++ in that respect. They are able to define private integral types (see e.g.