Annotated Ada Reference Manual — Legal Information

A.15 The Package Command_Line

The package Command_Line allows a program to obtain the values of its arguments and to set the exit status code to be returned on normal termination.

1.a/2

Implementation defined: The meaning of Argument_Count, Argument, and Command_Name for package Command_Line. The bounds of type Command_Line.Exit_Status.

Static Semantics

The library package Ada.Command_Line has the following declaration:

package Ada.Command_Line is
pragma Preelaborate(Command_Line);

function Argument_Count return Natural;

function Argument (Number : in Positive) return String;

function Command_Name return String;

type Exit_Status is implementation-defined integer type;

Success : constant Exit_Status;
Failure : constant Exit_Status;

procedure Set_Exit_Status (Code : in Exit_Status);

private
... -- not specified by the language
end Ada.Command_Line;

function Argument_Count return Natural;

If the external execution environment supports passing arguments to a program, then Argument_Count returns the number of arguments passed to the program invoking the function. Otherwise it returns 0. The meaning of “number of arguments” is implementation defined.

function Argument (Number : in Positive) return String;

If the external execution environment supports passing arguments to a program, then Argument returns an implementation-defined value corresponding to the argument at relative position Number. {Constraint_Error (raised by failure of run-time check)} If Number is outside the range 1..Argument_Count, then Constraint_Error is propagated.

14.a

Ramification: If the external execution environment does not support passing arguments to a program, then Argument(N) for any N will raise Constraint_Error, since Argument_Count is 0.

function Command_Name return String;

If the external execution environment supports passing arguments to a program, then Command_Name returns an implementation-defined value corresponding to the name of the command invoking the program; otherwise Command_Name returns the null string.

16.1/1

type Exit_Status is implementation-defined integer type;

The type Exit_Status represents the range of exit status values supported by the external execution environment. The constants Success and Failure correspond to success and failure, respectively.

procedure Set_Exit_Status (Code : in Exit_Status);

If the external execution environment supports returning an exit status from a program, then Set_Exit_Status sets Code as the status. Normal termination of a program returns as the exit status the value most recently set by Set_Exit_Status, or, if no such value has been set, then the value Success. If a program terminates abnormally, the status set by Set_Exit_Status is ignored, and an implementation-defined exit status value is set.

If the external execution environment does not support returning an exit value from a program, then Set_Exit_Status does nothing.

Implementation Permissions

An alternative declaration is allowed for package Command_Line if different functionality is appropriate for the external execution environment.

NOTES

36 Argument_Count, Argument, and Command_Name correspond to the C language's argc, argv[n] (for n>0) and argv[0], respectively.

22.a

To be honest: The correspondence of Argument_Count to argc is not direct — argc would be one more than Argument_Count, since the argc count includes the command name, whereas Argument_Count does not.

Extensions to Ada 83

22.b

{extensions to Ada 83} This clause is new in Ada 95.