The package Ada.Command_Line provides access to the command-line
arguments and program name. In order for this interface to operate
correctly, the two variables
int gnat_argc; char **gnat_argv;
are declared in one of the GNAT library routines. These variables must
be set from the actual argc and argv values passed to the
main program. With no ‘n’ present, gnatbind
generates the C main program to automatically set these variables.
If the ‘n’ switch is used, there is no automatic way to
set these variables. If they are not set, the procedures in
Ada.Command_Line will not be available, and any attempt to use
them will raise Constraint_Error. If command line access is
required, your main program must set gnat_argc and
gnat_argv from the argc and argv values passed to
it.