CODEWITHSUNDEEP
arraysstringadadynamic-allocation
Romil Agrawal
Romil Agrawal

Reputation: 71

String Arrays in Ada

I have a program in Ada95, in which I have to create an array of strings. This array can contain strings of variable length.

Example: I have declared the array in which all the indexes can store strings of size 50. When I assign a smaller string to the above array, I get "Constraint Error".

Code:

procedure anyname is
    input_array : array(1..5) of String(1..50);
begin
    input_array(1):="12345";
end anyname;

I have tried to create the array of Unbounded_Strings. But that doesn't work either. Can anyone tell me how to store this "12345" in the above string array?

Upvotes: 7

Views: 10072

Answers (4)

debater
debater

Reputation: 466

I've had a lot of joy from instantiating a container package, e.g.:

package String_Vectors is
   new Ada.Containers.Indefinite_Vectors (Positive, String);

It's still a bit fiddly, compared to how easy it is to mess about with strings in a lot of other programming languages, but it's okay.

Fundamentally, Ada is a language designed to be usable without using the heap (at all :-) Most other languages would fall down in a, well, a heap, without the heap.

Upvotes: 1

Adriana
Adriana

Reputation: 51

Strings in Ada are arrays of characters of fixed length. In order to use strings of variable length (which may often be the case when arrays of strings are needed, e.g. arrays of names, each name being of variable length), each individual string may be declared as an Unbounded_String. The only caveat is that this allocates from the heap memory. Below is a complete example of an array of strings in Ada.

with Ada.Text_IO; use Ada.Text_IO;
with Ada.Strings.Unbounded; use Ada.Strings.Unbounded;
with Ada.Strings.Unbounded.Text_IO; use Ada.Strings.Unbounded.Text_IO;

procedure arrayAda is
type DaysArray is array(1..7) of Unbounded_String;
days: DaysArray;
begin
    days(1):=To_Unbounded_String("Sunday");
    days(2):=To_Unbounded_String("Monday");
    days(3):=To_Unbounded_String("Tuesday");
    days(4):=To_Unbounded_String("Wednesday");
    days(5):=To_Unbounded_String("Thursday");
    days(6):=To_Unbounded_String("Friday");
    days(7):=To_Unbounded_String("Saturday");
    for index in 1..7 loop
        Put(days(index));
        Put("   ");
    end loop;
end arrayAda;

This produces the following output:

$ ./arrayAda
Sunday   Monday   Tuesday   Wednesday   Thursday   Friday   Saturday

Upvotes: 1

ajb
ajb

Reputation: 31689

If you use Unbounded_String, you cannot assign a string literal to it directly. String literals can have type String, Wide_String, or Wide_Wide_String, but nothing else; and assignment in Ada usually requires that the destination and source be the same type. To convert a String to an Unbounded_String, you need to call the To_Unbounded_String function:

procedure anyname is
    input_array : array(1..5) of Ada.Strings.Unbounded.Unbounded_String;
begin
    input_array(1) := Ada.Strings.Unbounded.To_Unbounded_String ("12345");
end anyname;

You can shorten the name by using a use clause; some other programmers might define their own renaming function, possibly even using the unary "+" operator:

function "+" (Source : String) return Ada.Strings.Unbounded.Unbounded_String
    renames Ada.Strings.Unbounded.To_Unbounded_String;

procedure anyname is
    input_array : array(1..5) of Ada.Strings.Unbounded.Unbounded_String;
begin
    input_array(1) := +"12345";  -- uses renaming "+" operator
end anyname;

Not everyone likes this style.

Upvotes: 9

trashgod
trashgod

Reputation: 205775

You can use Ada.Strings.Unbounded, illustrated here, or you can use a static ragged array, illustrated here. The latter approach uses an array of aliased components, each of which may have a different length.

type String_Access is access constant String;

String_5: aliased constant String := "12345";
String_6: aliased constant String := "123456";
String_7: aliased constant String := "1234567";
...

Input_Array: array (1..N) of
   String_Access :=
      (1 => String_5'Access,
       2 => String_6'Access,
       3 => String_7'Access,
       -- etc. up to N
      );

Upvotes: 1

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