Next: , Previous: F.3.2, Up: F.3


F.3.3 The Package Text_IO.Editing

1
The package Text_IO.Editing provides a private type Picture with associated operations, and a generic package Decimal_Output. An object of type Picture is composed from a well−formed picture String (see F.3.1) and a Boolean item indicating whether a zero numeric value will result in an edited output string of all space characters. The package Decimal_Output contains edited output subprograms implementing the effects defined in F.3.2.

Static Semantics

2
The library package Text_IO.Editing has the following declaration:

3

     package Ada.Text_IO.Editing is

4

        type Picture is private;

5

        function Valid (Pic_String      in String;
                        Blank_When_Zero in Boolean := False) return Boolean;

6

        function To_Picture (Pic_String      in String;
                             Blank_When_Zero in Boolean := False)
           return Picture;

7

        function Pic_String      (Pic in Picture) return String;
        function Blank_When_Zero (Pic in Picture) return Boolean;

8

        Max_Picture_Length  constant := implementation_defined;

9

        Picture_Error       exception;

10

        Default_Currency    constant String    := "$";
        Default_Fill        constant Character := '*';
        Default_Separator   constant Character := ',';
        Default_Radix_Mark  constant Character := '.';

11

        generic
           type Num is delta <> digits <>;
           Default_Currency   in String    := Text_IO.Editing.Default_Currency;
           Default_Fill       in Character := Text_IO.Editing.Default_Fill;
           Default_Separator  in Character :=
                                   Text_IO.Editing.Default_Separator;
           Default_Radix_Mark in Character :=
                                   Text_IO.Editing.Default_Radix_Mark;
        package Decimal_Output is
           function Length (Pic      in Picture;
                            Currency in String := Default_Currency)
              return Natural;

12

           function Valid (Item     in Num;
                           Pic      in Picture;
                           Currency in String := Default_Currency)
              return Boolean;

13

           function Image (Item       in Num;
                           Pic        in Picture;
                           Currency   in String    := Default_Currency;
                           Fill       in Character := Default_Fill;
                           Separator  in Character := Default_Separator;
                           Radix_Mark in Character := Default_Radix_Mark)
              return String;

14

           procedure Put (File       in File_Type;
                          Item       in Num;
                          Pic        in Picture;
                          Currency   in String    := Default_Currency;
                          Fill       in Character := Default_Fill;
                          Separator  in Character := Default_Separator;
                          Radix_Mark in Character := Default_Radix_Mark);

15

           procedure Put (Item       in Num;
                          Pic        in Picture;
                          Currency   in String    := Default_Currency;
                          Fill       in Character := Default_Fill;
                          Separator  in Character := Default_Separator;
                          Radix_Mark in Character := Default_Radix_Mark);

16

           procedure Put (To         out String;
                          Item       in Num;
                          Pic        in Picture;
                          Currency   in String    := Default_Currency;
                          Fill       in Character := Default_Fill;
                          Separator  in Character := Default_Separator;
                          Radix_Mark in Character := Default_Radix_Mark);
        end Decimal_Output;
     private
        ... −− not specified by the language
     end Ada.Text_IO.Editing;

16.a

Implementation defined: The value of Max_Picture_Length in the package Text_IO.Editing

17
The exception Constraint_Error is raised if the Image function or any of the Put procedures is invoked with a null string for Currency.

18

     function Valid (Pic_String      in String;
                     Blank_When_Zero in Boolean := False) return Boolean;

19

Valid returns True if Pic_String is a well−formed picture String (see F.3.1) the length of whose expansion does not exceed Max_Picture_Length, and if either Blank_When_Zero is False or Pic_String contains no '*'.

20

     function To_Picture (Pic_String      in String;
                          Blank_When_Zero in Boolean := False)
        return Picture;

21

To_Picture returns a result Picture such that the application of the function Pic_String to this result yields an expanded picture String equivalent to Pic_String, and such that Blank_When_Zero applied to the result Picture is the same value as the parameter Blank_When_Zero. Picture_Error is raised if not Valid(Pic_String, Blank_When_Zero).

22

     function Pic_String      (Pic in Picture) return String;
     
     function Blank_When_Zero (Pic in Picture) return Boolean;

23

If Pic is To_Picture(String_Item, Boolean_Item) for some String_Item and Boolean_Item, then:

24

25

26

If Pic_1 and Pic_2 are objects of type Picture, then "="(Pic_1, Pic_2) is True when

27

28

29

     function Length (Pic      in Picture;
                      Currency in String := Default_Currency)
        return Natural;

30

Length returns Pic_String(Pic)'Length + Currency_Length_Adjustment −− Radix_Adjustment where

31

32

33

34

35

36

37

     function Valid (Item     in Num;
                     Pic      in Picture;
                     Currency in String := Default_Currency)
        return Boolean;

38

Valid returns True if Image(Item, Pic, Currency) does not raise Layout_Error, and returns False otherwise.

39

     function Image (Item       in Num;
                     Pic        in Picture;
                     Currency   in String    := Default_Currency;
                     Fill       in Character := Default_Fill;
                     Separator  in Character := Default_Separator;
                     Radix_Mark in Character := Default_Radix_Mark)
        return String;

40

Image returns the edited output String as defined in F.3.2 for Item, Pic_String(Pic), Blank_When_Zero(Pic), Currency, Fill, Separator, and Radix_Mark. If these rules identify a layout error, then Image raises the exception Layout_Error.

41

     procedure Put (File       in File_Type;
                    Item       in Num;
                    Pic        in Picture;
                    Currency   in String    := Default_Currency;
                    Fill       in Character := Default_Fill;
                    Separator  in Character := Default_Separator;
                    Radix_Mark in Character := Default_Radix_Mark);
     
     procedure Put (Item       in Num;
                    Pic        in Picture;
                    Currency   in String    := Default_Currency;
                    Fill       in Character := Default_Fill;
                    Separator  in Character := Default_Separator;
                    Radix_Mark in Character := Default_Radix_Mark);

42

Each of these Put procedures outputs Image(Item, Pic, Currency, Fill, Separator, Radix_Mark) consistent with the conventions for Put for other real types in case of bounded line length (see A.10.6, "A.10.6 Get and Put Procedures").

43

     procedure Put (To         out String;
                    Item       in Num;
                    Pic        in Picture;
                    Currency   in String    := Default_Currency;
                    Fill       in Character := Default_Fill;
                    Separator  in Character := Default_Separator;
                    Radix_Mark in Character := Default_Radix_Mark);

44

Put copies Image(Item, Pic, Currency, Fill, Separator, Radix_Mark) to the given string, right justified. Otherwise unassigned Character values in To are assigned the space character. If To'Length is less than the length of the string resulting from Image, then Layout_Error is raised.
Implementation Requirements

45
Max_Picture_Length shall be at least 30. The implementation shall support currency strings of length up to at least 10, both for Default_Currency in an instantiation of Decimal_Output, and for Currency in an invocation of Image or any of the Put procedures.

45.a

Discussion: This implies that a picture string with character replications need not be supported (i.e., To_Picture will raise Picture_Error) if its expanded form exceeds 30 characters.

     NOTES

46

 The rules for edited output are based on COBOL (ANSI X3.23:1985, endorsed by ISO as ISO 1989−1985), with the following differences:

47

48

49

50

51

52

52.1

The value of 30 for Max_Picture_Length is the same limit as in COBOL.

52.a

Reason: There are several reasons we have not adopted the COBOL−style permission to provide a single−character replacement in the picture string for the `$' as currency symbol, or to interchange the roles of `.' and `,' in picture strings

52.b

52.c

52.d