Question

If a value is defined as

#define M_40 40

Is the size the same as a short (2 bytes) or is it as a char (1 byte) or int (4 bytes)?

Is the size dependent on whether you are 32-bit or 64-bit?

Answer 1

#define has no size as it’s not a type but a plain text substitution into your C++ code. #define is a preprocessing directive and it runs before your code even begins to be compiled .

The size in C++ code after substitution is whatever the size is of what C++ expression or code you have there. For example if you suffix with L like 102L then it is seen a long, otherwise with no suffix, just an int. So 4 bytes on x86 and x64 probably, but this is compiler dependent.

Perhaps the C++ standard’s Integer literal section will clear it up for you (Section 2.13.1-2 of the C++03 standard):

The type of an integer literal depends
on its form, value, and suffix. If it
is decimal and has no suffix, it has
the first of these types in which its
value can be represented: int, long
int; if the value cannot be
represented as a long int, the
behavior is undefined. If it is octal
or hexadecimal and has no suffix, it
has the first of these types in which
its value can be represented: int,
unsigned int, long int, unsigned long
int. If it is suffixed by u or U, its
type is the first of these types in
which its value can be represented:
unsigned int, unsigned long int. If it
is suffixed by l or L, its type is the
first of these types in which its
value can be represented: long int,
unsigned long int. If it is suffixed
by ul, lu, uL, Lu, Ul, lU, UL, or LU,
its type is unsigned long int