Attribute Image

Introduction#

Subtype attributes 'Image and 'Value will take, respectively, a scalar value and a string and they return, respectively, a string and a scalar value. The result of 'Image can be input to 'Value to get the original value. The converse is also true.

The __Scalar_Object__'Image attribute can be used directly on objects (since Ada 2012-TC-1).

Syntax#

function Scalar’Image (Argument : Scalar’Base) return String;
function Discrete’Image (Argument : Discrete’Base) return String;
function Integer’Image (Argument : Integer’Base) return String;
function Enumeration’Image (Argument : Enumeration’Base) return String;
function Real’Image (Argument : Real’Base) return String;
function Numeric’Image (Argument : Numeric’Base) return String;
function Scalar’Value (Argument : String) return Scalar’Base;
function Discrete’Value (Argument : String) return Discrete’Base;
function Integer’Value (Argument : String) return Integer’Base;
function Enumeration’Value (Argument : String) return Enumeration’Base;
function Real’Value (Argument : String) return Real’Base;
function Scalar_Object‘Image return String;

Remarks#

Note that 'Image can incur implementation defined results (RM 3.5), namely when some graphic characters needed for the String result are not defined in Character. Consider the larger repertoires of 'Wide_Image and 'Wide_Wide_Image.

The permission to use the attribute __Scalar_Object__'Image directly on an object was added in Ada 2012-TC-1 (April 2016).

Print out float using the Image attribute

with Ada.Text_IO;

procedure Main is
   type Some_Float digits 8 range 0.0 .. 10.0;
   X : Some_Float := 2.71;
begin
   Ada.Text_IO.Put_Line (X'Image);
end Main;

Result

2.71000E+00

Print out integer using the Image attribute

with Ada.Text_IO;

procedure Main is
   type Some_Integer is range -42 .. 42;
   X : Some_Integer := 17;
begin
   Ada.Text_IO.Put_Line (X'Image);
end Main;

Result

Print out enumeration using the Image attribute

with Ada.Text_IO;

procedure Main is
   type Fruit is (Banana, Orange, Pear);
   X : Fruit := Orange;
begin
   Ada.Text_IO.Put_Line (X'Image);
   Ada.Text_IO.Put_Line (Pear'Image);
end Main;

Result

ORANGE
PEAR

Print out Enumeration using attribute Image

with Ada.Text_IO;

procedure Main is
   type Fruit is (Banana, Orange, Pear);
   X : Fruit := Orange;
begin
   Ada.Text_IO.Put_Line (Fruit'Image (X));
end Main;

Result

ORANGE

Print out Integer using attribute Image

with Ada.Text_IO;

procedure Main is
   X : Integer := 17;
begin
   Ada.Text_IO.Put_Line (Integer'Image (X));
end Main;

Result

Print out Float using attribute Image

with Ada.Text_IO;

procedure Main is
   X : Float := 2.71;
begin
   Ada.Text_IO.Put_Line (Float'Image (X));
end Main;

Result

2.71000E+00

As Inverses

with Ada.Text_IO;

procedure Image_And_Value is
   type Fruit is (Banana, Orange, Pear);
   X  : Fruit := Orange;
begin
   Ada.Text_IO.Put_Line (Boolean'Image
      (Fruit'Value (Fruit'Image (X)) = X
          and
       Fruit'Image (Fruit'Value ("ORANGE")) = "ORANGE"));
end Image_And_Value;

Result

TRUE