gcc/ada/g-decstr.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUN-TIME COMPONENTS                         --
   4 --                                                                          --
   5 --                    G N A T . D E C O D E _ S T R I N G                   --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --                       Copyright (C) 2007, AdaCore                        --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  19 -- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
  20 -- Boston, MA 02110-1301, USA.                                              --
  21 --                                                                          --
  22 -- As a special exception,  if other files  instantiate  generics from this --
  23 -- unit, or you link  this unit with other files  to produce an executable, --
  24 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  25 -- covered  by the  GNU  General  Public  License.  This exception does not --
  26 -- however invalidate  any other reasons why  the executable file  might be --
  27 -- covered by the  GNU Public License.                                      --
  28 --                                                                          --
  29 -- GNAT was originally developed  by the GNAT team at  New York University. --
  30 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  31 --                                                                          --
  32 ------------------------------------------------------------------------------
  33
  34 --  This generic package provides utility routines for converting from an
  35 --  encoded string to a corresponding Wide_String or Wide_Wide_String value
  36 --  using a specified encoding convention, which is supplied as the generic
  37 --  parameter. UTF-8 is handled especially efficiently, and if the encoding
  38 --  method is known at compile time to be WCEM_UTF8, then the instantiation
  39 --  is specialized to handle only the UTF-8 case and exclude code for the
  40 --  other encoding methods. The package also provides positioning routines
  41 --  for skipping encoded characters in either direction, and for validating
  42 --  strings for correct encodings.
  43
  44 --  Note: this package is only about decoding sequences of 8-bit characters
  45 --  into corresponding 16-bit Wide_String or 32-bit Wide_Wide_String values.
  46 --  It knows nothing at all about the character encodings being used for the
  47 --  resulting Wide_Character and Wide_Wide_Character values. Most often this
  48 --  will be Unicode/ISO-10646 as specified by the Ada RM, but this package
  49 --  does not make any assumptions about the character coding. See also the
  50 --  packages Ada.Wide_[Wide_]Characters.Unicode for unicode specific functions.
  51
  52 --  Note on the use of brackets encoding (WCEM_Brackets). The brackets encoding
  53 --  method is ambiguous in the context of this package, since there is no way
  54 --  to tell if ["1234"] is eight unencoded characters or one encoded character.
  55 --  In the context of Ada sources, any sequence starting [" must be the start
  56 --  of an encoding (since that sequence is not valid in Ada source otherwise).
  57 --  The routines in this package use the same approach. If the input string
  58 --  contains the sequence [" then this is assumed to be the start of a brackets
  59 --  encoding sequence, and if it does not match the syntax, an error is raised.
  60 --  In the case of the Prev functions, a sequence ending with "] is assumed to
  61 --  be a valid brackets sequence, and an error is raised if it is not.
  62
  63 with System.WCh_Con;
  64
  65 generic
  66    Encoding_Method : System.WCh_Con.WC_Encoding_Method;
  67
  68 package GNAT.Decode_String is
  69    pragma Pure;
  70
  71    function Decode_Wide_String (S : String) return Wide_String;
  72    pragma Inline (Decode_Wide_String);
  73    --  Decode the given String, which is encoded using the indicated coding
  74    --  method, returning the corresponding decoded Wide_String value. If S
  75    --  contains a character code that cannot be represented with the given
  76    --  encoding, then Constraint_Error is raised.
  77
  78    procedure Decode_Wide_String
  79      (S      : String;
  80       Result : out Wide_String;
  81       Length : out Natural);
  82    --  Similar to the above function except that the result is stored in the
  83    --  given Wide_String variable Result, starting at Result (Result'First). On
  84    --  return, Length is set to the number of characters stored in Result. The
  85    --  caller must ensure that Result is long enough (an easy choice is to set
  86    --  the length equal to the S'Length, since decoding can never increase the
  87    --  string length). If the length of Result is insufficient Constraint_Error
  88    --  will be raised.
  89
  90    function Decode_Wide_Wide_String (S : String) return Wide_Wide_String;
  91    pragma Inline (Decode_Wide_Wide_String);
  92    --  Same as above function but for Wide_Wide_String output
  93
  94    procedure Decode_Wide_Wide_String
  95      (S      : String;
  96       Result : out Wide_Wide_String;
  97       Length : out Natural);
  98    --  Same as above procedure, but for Wide_Wide_String output
  99
 100    function Validate_Wide_String (S : String) return Boolean;
 101    --  This function inspects the string S to determine if it contains only
 102    --  valid encodings corresponding to Wide_Character values using the
 103    --  given encoding. If a call to Decode_Wide_String (S) would return
 104    --  without raising Constraint_Error, then Validate_Wide_String will
 105    --  return True. If the call would have raised Constraint_Error, then
 106    --  Validate_Wide_String will return False.
 107
 108    function Validate_Wide_Wide_String (S : String) return Boolean;
 109    --  Similar to Validate_Wide_String, except that it succeeds if the string
 110    --  contains only encodings corresponding to Wide_Wide_Character values.
 111
 112    procedure Decode_Wide_Character
 113      (Input  : String;
 114       Ptr    : in out Natural;
 115       Result : out Wide_Character);
 116    pragma Inline (Decode_Wide_Character);
 117    --  This is a lower level procedure that decodes a single character using
 118    --  the given encoding method. The encoded character is stored in Input,
 119    --  starting at Input (Ptr). The resulting output character is stored in
 120    --  Result, and on return Ptr is updated past the input character or
 121    --  encoding sequence. Constraint_Error will be raised if the input has
 122    --  has a character that cannot be represented using the given encoding,
 123    --  or if Ptr is outside the bounds of the Input string.
 124
 125    procedure Decode_Wide_Wide_Character
 126      (Input  : String;
 127       Ptr    : in out Natural;
 128       Result : out Wide_Wide_Character);
 129    --  Same as above procedure but with Wide_Wide_Character input
 130
 131    procedure Next_Wide_Character (Input : String; Ptr : in out Natural);
 132    --  This procedure examines the input string starting at Input (Ptr), and
 133    --  advances Ptr past one character in the encoded string, so that on return
 134    --  Ptr points to the next encoded character. Constraint_Error is raised if
 135    --  an invalid encoding is encountered, or the end of the string is reached
 136    --  or if Ptr is less than String'First on entry, or if the character
 137    --  skipped is not a valid Wide_Character code. This call may be more
 138    --  efficient than calling Decode_Wide_Character and discarding the result.
 139
 140    procedure Prev_Wide_Character (Input : String; Ptr : in out Natural);
 141    --  This procedure is similar to Next_Encoded_Character except that it moves
 142    --  backwards in the string, so that on return, Ptr is set to point to the
 143    --  previous encoded character. Constraint_Error is raised if the start of
 144    --  the string is encountered. It is valid for Ptr to be one past the end
 145    --  of the string for this call (in which case on return it will point to
 146    --  the last encoded character).
 147    --
 148    --  Note: it is not generally possible to do this function efficiently with
 149    --  all encodings, the current implementation is only efficient for the case
 150    --  of UTF-8 (Encoding_Method = WCEM_UTF8) and Brackets (Encoding_Method =
 151    --  WCEM_Brackets). For all other encodings, we work by starting at the
 152    --  beginning of the string and moving forward till Ptr is reached, which
 153    --  is correct but slow.
 154
 155    procedure Next_Wide_Wide_Character (Input : String; Ptr : in out Natural);
 156    --  Similar to Next_Wide_Character except that codes skipped must be valid
 157    --  Wide_Wide_Character codes.
 158
 159    procedure Prev_Wide_Wide_Character (Input : String; Ptr : in out Natural);
 160    --  Similar to Prev_Wide_Character except that codes skipped must be valid
 161    --  Wide_Wide_Character codes.
 162
 163 end GNAT.Decode_String;