A.15 The Package Command_Line
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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.
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. If Number is outside the range 1..Argument_Count, then Constraint_Error is propagated.
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.
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.
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Ada Reference Manual