3.6.3 String Types
Static Semantics
1
{string type}
A one-dimensional array type whose component type
is a character type is called a
string type.
2/2
{
AI95-00285-01}
[There are
three two
predefined string types, String
, and Wide_String
, and Wide_Wide_String,
each indexed by values of the predefined subtype Positive; these are
declared in the visible part of package Standard:]
3
[subtype Positive is Integer range 1 .. Integer'Last;
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{
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type String
is array(Positive
range <>)
of Character;
type Wide_String
is array(Positive
range <>)
of Wide_Character;
type Wide_Wide_String is array(Positive range <>) of Wide_Wide_Character;
]
5
51 String literals (see
2.6
and
4.2) are defined for all string types.
The concatenation operator & is predefined for string types, as for
all nonlimited one-dimensional array types. The ordering operators <,
<=, >, and >= are predefined for string types, as for all one-dimensional
discrete array types; these ordering operators correspond to lexicographic
order (see
4.5.2).
Examples
6
Examples of string
objects:
7
Stars : String(1 .. 120) := (1 .. 120 => '*' );
Question : constant String := "How many characters?";
-- Question'First = 1, Question'Last = 20
-- Question'Length = 20 (the number of characters)
8
Ask_Twice : String := Question & Question; --
constrained to (1..40)
Ninety_Six :
constant Roman := "XCVI"; --
see 3.5.2 and 3.6Inconsistencies With Ada 83
8.a
{
inconsistencies with Ada 83}
The
declaration of Wide_String in Standard hides a use-visible declaration
with the same
defining_identifier. In rare
cases, this might result in an inconsistency between Ada 83 and Ada 95.
Incompatibilities With Ada 83
8.b
{
incompatibilities with Ada 83}
Because
both String and Wide_String are always directly visible, an expression
like
8.c
"a" < "bc"
8.d
is now ambiguous, whereas in Ada 83 both string
literals could be resolved to type String.
Extensions to Ada 83
8.e
{
extensions to Ada 83}
The
type Wide_String is new (though it was approved by ARG for Ada 83 compilers
as well).
Wording Changes from Ada 83
8.f
We define the term string type as a natural
analogy to the term character type.
Inconsistencies With Ada 95
8.g/2
{
AI95-00285-01}
{inconsistencies with Ada 95} The
declaration of Wide_Wide_String in Standard hides a use-visible declaration
with the same defining_identifier. In the
(very) unlikely event that an Ada 95 program had depended on such a use-visible
declaration, and the program remains legal after the substitution of
Standard.Wide_Wide_String, the meaning of the program will be different.
Extensions to Ada 95
8.h/2
{
AI95-00285-01}
{extensions to Ada 95} The
type Wide_Wide_String is new.
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