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2.85 Pragma Initialize_Scalars

Syntax:

pragma Initialize_Scalars
  [ ( TYPE_VALUE_PAIR {, TYPE_VALUE_PAIR} ) ];

TYPE_VALUE_PAIR ::=
  SCALAR_TYPE => static_EXPRESSION

SCALAR_TYPE :=
  Short_Float
| Float
| Long_Float
| Long_Long_Flat
| Signed_8
| Signed_16
| Signed_32
| Signed_64
| Unsigned_8
| Unsigned_16
| Unsigned_32
| Unsigned_64

This pragma is similar to Normalize_Scalars conceptually but has two important differences.

First, there is no requirement for the pragma to be used uniformly in all units of a partition. In particular, it is fine to use this just for some or all of the application units of a partition, without needing to recompile the run-time library. In the case where some units are compiled with the pragma, and some without, then a declaration of a variable where the type is defined in package Standard or is locally declared will always be subject to initialization, as will any declaration of a scalar variable. For composite variables, whether the variable is initialized may also depend on whether the package in which the type of the variable is declared is compiled with the pragma.

The other important difference is that the programmer can control the value used for initializing scalar objects. This effect can be achieved in several different ways:

Note that pragma Initialize_Scalars is particularly useful in conjunction with the enhanced validity checking that is now provided in GNAT, which checks for invalid values under more conditions. Using this feature (see description of the `-gnatV' flag in the GNAT User’s Guide) in conjunction with pragma Initialize_Scalars provides a powerful new tool to assist in the detection of problems caused by uninitialized variables.

Note: the use of Initialize_Scalars has a fairly extensive effect on the generated code. This may cause your code to be substantially larger. It may also cause an increase in the amount of stack required, so it is probably a good idea to turn on stack checking (see description of stack checking in the GNAT User’s Guide) when using this pragma.


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