Posted By: Anonymous
I am transitioning from Java to C++ and have some questions about the
long data type. In Java, to hold an integer greater than 232, you would simply write
long x;. However, in C++, it seems that
long is both a data type and a modifier.
There seems to be several ways to use
long x; long long x; long int x; long long int x;
Also, it seems there are things such as:
long double x;
and so on.
What is the difference between all of these various data types, and do they all have the same purpose?
long int are identical. So are
long long and
long long int. In both cases, the
int is optional.
As to the difference between the two sets, the C++ standard mandates minimum ranges for each, and that
long long is at least as wide as
The controlling parts of the standard (C++11, but this has been around for a long time) are, for one,
3.9.1 Fundamental types, section 2 (a later section gives similar rules for the unsigned integral types):
There are five standard signed integer types : signed char, short int, int, long int, and long long int. In this list, each type provides at least as much storage as those preceding it in the list.
There’s also a table 9 in
18.104.22.168 Simple type specifiers, which shows the “mappings” of the specifiers to actual types (showing that the
int is optional), a section of which is shown below:
Specifier(s) Type ------------- ------------- long long int long long int long long long long int long int long int long long int
Note the distinction there between the specifier and the type. The specifier is how you tell the compiler what the type is but you can use different specifiers to end up at the same type.
long on its own is neither a type nor a modifier as your question posits, it’s simply a specifier for the
long int type. Ditto for
long long being a specifier for the
long long int type.
Although the C++ standard itself doesn’t specify the minimum ranges of integral types, it does cite C99, in
1.2 Normative references, as applying. Hence the minimal ranges as set out in
C99 22.214.171.124.1 Sizes of integer types <limits.h> are applicable.
In terms of
long double, that’s actually a floating point value rather than an integer. Similarly to the integral types, it’s required to have at least as much precision as a
double and to provide a superset of values over that type (meaning at least those values, not necessarily more values).