Ada Programming/Attributes/'Size

Attributes 'Size __TOC__ Description R'Size is a representation attribute used to get the number of bits of an object or type: When applied to an object, 'Size yields the actual number of bits allocated to store the object. When applied to a subtype, 'Size yields the smallest n such that all values fit in the range 0 .. 2n-1 for only positive values, else -2n-1 .. 2n-1-1. The 'Size attribute may also be used in an attribute definition clause to set the size for a first subtype. In special cases, it is even possible to force a biased representation by using a smaller value than the n above. Examples This subtype allows a biased representation with only three bits because it comprises only eight values: type T is range 1000 .. 1007; for T'Size use 3; Without the size clause, T'Size would return 10 because 210-1 = 1023. attributes_size.adb with Ada Text_IO; procedure Attributes_Size is package T_IO renames Ada.Text_IO; package I_IO is new Ada.Text_IO.Integer_IO (Integer); A_Boolean : constant Boolean := True; begin T_IO.Put ("Size of Boolean type = "); An enumeration with I_IO.Put (Boolean'Size); 2 values fits into T_IO.New_Line; 1 bit. T_IO.Put ("Size of Boolean Object = "); it is more efficient I_IO.Put (A_Boolean'Size); to store a boolean T_IO.New_Line; as an entire byte end Attributes_Size; The output with GNAT 10.2.0 will be: Size of Boolean type = 1 Size of Boolean Object = 8 Try it yourself and see how your compiler does. The value of Size can also be specified using an attribute definition clause. For example, the following declarations specify a C99 compatible bool: type Bool is new Boolean; for Bool'Size use Interfaces C.int'Size; Incorrect usages See also Wikibook Ada Programming Ada Programming/Attributes Ada Programming/Attributes/'Component Size Ada Programming/Attributes/'Max Size In Storage Elements Ada Programming/Attributes/'Value Size (implementation defined) Ada Programming/Attributes/'Object Size (implementation defined) Ada 83 Reference Manual 13 7 2 Representation Attributes A Predefined Language Attributes Ada 95 Reference Manual 13 3 Operational and Representation Attributes K Language-Defined Attributes Ada 2005 Reference Manual 13 3 Operational and Representation Attributes K Language-Defined Attributes Ada 2012 Reference Manual 13 3 Operational and Representation Attributes K Language-Defined Aspects and Attributes Size Size