Re: function Is_Open (File : File_Type) return Boolean; :Text_io

[Simon Wright <simon@pushface.org>]

comicfanzine@gmail.com writes:

> Thanks fot link .
>
> I want to create+open a file then use Is_Open , if the file have been create i  want to put some text + the value of Is_Open(should be TRUE) .
>
> There is french in the code :
>
> [code]WITH Ada.Text_IO ;  USE Ada.Text_IO ; 
>
> PROCEDURE TestFichier IS
>
>    MonFichier : File_type ; 
>    
> BEGIN 
>    Create( MonFichier,Name => "clone.adb");
>    open(MonFichier,In_file,"clone.adb") ;
>     if Is_Open(MonFichier) and MonFichier = true 
>     then put("Le fichier , ouvert ? : ",MonFichier);
>     end if;
> END TestFichier ;[/code]

Compiling this with listing (gnatmake -gnatl testfichier.adb) gives

     3. PROCEDURE TestFichier IS
     4.
     5.    MonFichier : File_type ;
     6.    
     7. BEGIN
     8.    Create( MonFichier,Name => "clone.adb");
     9.    open(MonFichier,In_file,"clone.adb") ;
    10.     if Is_Open(MonFichier) and MonFichier = true
                                                  |
        >>> invalid operand types for operator "="
        >>> left operand has private type "Ada.Text_Io.File_Type"
        >>> right operand has type "Standard.Boolean"
    11.     then put("Le fichier , ouvert ? : ",MonFichier);
                 1   3
        >>> no candidate interpretations match the actuals:
        >>> too many arguments in call to "put"
        >>> expected private type "Ada.Text_Io.File_Type"
        >>> found a string type
        >>>   ==> in call to "Put" at a-textio.ads:241
        >>>   ==> in call to "Put" at a-textio.ads:207

    12.     end if;
    13. END TestFichier ;

First, the compiler messages:

Line 10
-------
Is_Open returns Boolean, and MonFichier is a File_Type and can't be
compared to Boolean (in fact, it's limited private, so it can't by
default be compared to anything!) so I think you just meant

   if Is_Open (MonFichier)

Line 11
-------
You have the arguments the wrong way round. You could use named
parameter association if you insist on this order,

   Put (Item => "Le fichier , ouvert ? : ", File => MonFichier);

==============================

Second, the semantic problems: Create at line 8 will either result in an
opened writable file (MonFichier) or will raise an exception if the file
already existed.

If you get to line 9 (i.e. the Create was successful) you will get an
exception because the file is already open.

If you were to get to line 10, Is_Open would have to return True.

If you were to get to line 11 having executed line 9, you would get an
exception because you opened MonFichier read-only.