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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.

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.

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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