Re: Is there some way of calling a system command?

[adambeneschan@gmail.com]

On Tuesday, November 26, 2013 7:35:26 AM UTC-8, tolkamp wrote:
> Op zondag 11 juni 2006 15:19:12 UTC+2 schreef jimmaure...@worldnet.att.net:

> > The easiest way is to simply call the C system command.
> > The example below was run on my Windows XP system.
> 
> > with Interfaces.C.Strings;
> > use Interfaces.C.Strings;
> 
> > procedure System_Example is
> >    function System_Call(Command : Chars_Ptr) return Interfaces.C.Int;
> >    pragma Import(Convention => C, Entity => System_Call,
> >       External_Name => "system");
> >    Rc : Interfaces.C.Int;
> 
> > begin
> >    Rc := System_Call(New_String("dir"));
> > end System_Example;

> > The important part of the example is the creation of a function
> > specification I have named System_Call. That function specification
> > take a parameter of Chars_Ptr, which corresponds to a C char *.
> > The function specification is used as the Ada interface to the C
> > system call. The compiler is notified of that association through 
> > the pragma Import. That pragma causes the compiler to link the C
> > system command and call it whenever System_Call is called in the
> > Ada code.

> Thank you for your reaction.
> For me this is not very understandable.
> Where must I put the directory path to the executable?
> Is this "dir" in  Rc := System_Call(New_String("dir"));?

No, "dir" is the command.  The effect of this statement is that it will execute the "dir" command just as if a user had typed it into the Command Prompt window.  On Windows, "dir" causes a directory listing to appear on the screen.

System_Call (that is, the C system() routine) more or less requires a string that is something the user would type in a shell or a Command Prompt window.  So if you want to include the directory path, just include it as part of the command, same as you would if you typed it in yourself:

   Rc := System_Call(New_String("c:\users\abc\subdirectory\mytool"));

or use the Ada.Directories and possibly Ada.Directories.Hierarchical_File_Names to create the file name:

   Dir : constant String := "c:\users\abc\subdirectory";
   
   Rc := System.Call(New_String(Ada.Directories.Compose(Dir, "mytool")));

                                   -- Adam