A.15 The Package Command_Line
1
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
2
The library package
Ada.Command_Line has the following declaration:
3
package Ada.Command_Line
is
pragma Preelaborate(Command_Line);
4
function Argument_Count
return Natural;
5
function Argument (Number :
in Positive)
return String;
6
function Command_Name
return String;
7
type Exit_Status
is implementation-defined integer type;
8
Success :
constant Exit_Status;
Failure :
constant Exit_Status;
9
procedure Set_Exit_Status (Code :
in Exit_Status);
10
private
... -- not specified by the language
end Ada.Command_Line;
11
function Argument_Count return Natural;
12
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.
13
function Argument (Number : in Positive) return String;
14
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.
15
function Command_Name return String;
16
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;
17
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.
18
procedure Set_Exit_Status (Code : in Exit_Status);
19
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.
20
{unspecified
[partial]} If the external execution
environment does not support returning an exit value from a program,
then Set_Exit_Status does nothing.
Implementation Permissions
21
An alternative declaration is allowed for package
Command_Line if different functionality is appropriate for the external
execution environment.
22
37 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.
Sponsored by Ada-Europe