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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
Implementation defined: The
meaning of Argument_Count, Argument, and Command_Name.
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;
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function Command_Name return String;
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type Exit_Status is implementation-defined integer type;
8
Success : constant Exit_Status;
Failure : constant Exit_Status;
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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
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.
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