'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?

arraysstringadadynamic-allocation


Solution 1:[1]

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
      );

Solution 2:[2]

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

Solution 3:[3]

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.

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 Community
Solution 2
Solution 3

Related Questions