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) 2007-2013, 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 3,  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.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNAT was originally developed  by the GNAT team at  New York University. --
  28 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 --  This generic package provides utility routines for converting from an
  33 --  encoded string to a corresponding Wide_String or Wide_Wide_String value
  34 --  using a specified encoding convention, which is supplied as the generic
  35 --  parameter. UTF-8 is handled especially efficiently, and if the encoding
  36 --  method is known at compile time to be WCEM_UTF8, then the instantiation
  37 --  is specialized to handle only the UTF-8 case and exclude code for the
  38 --  other encoding methods. The package also provides positioning routines
  39 --  for skipping encoded characters in either direction, and for validating
  40 --  strings for correct encodings.
  41
  42 --  Note: this package is only about decoding sequences of 8-bit characters
  43 --  into corresponding 16-bit Wide_String or 32-bit Wide_Wide_String values.
  44 --  It knows nothing at all about the character encodings being used for the
  45 --  resulting Wide_Character and Wide_Wide_Character values. Most often this
  46 --  will be Unicode/ISO-10646 as specified by the Ada RM, but this package
  47 --  does not make any assumptions about the character coding. See also the
  48 --  packages Ada.Wide_[Wide_]Characters.Unicode for unicode specific functions.
  49
  50 --  In particular, in the case of UTF-8, all valid UTF-8 encodings, as listed
  51 --  in table 3.6 of the Unicode Standard, version 6.2.0, are recognized as
  52 --  legitimate. This includes the full range 16#0000_0000# .. 16#03FF_FFFF#.
  53 --  This includes codes in the range 16#D800# - 16#DFFF#. These codes all
  54 --  have UTF-8 encoding sequences that are well-defined (e.g. the encoding for
  55 --  16#D800# is ED A0 80). But these codes do not correspond to defined Unicode
  56 --  characters and are thus considered to be "not well-formed" (see table 3.7
  57 --  of the Unicode Standard). If you need to exclude these codes, you must do
  58 --  that manually, e.g. use Decode_Wide_Character/Decode_Wide_String and check
  59 --  that the resulting code(s) are not in this range.
  60
  61 --  Note on the use of brackets encoding (WCEM_Brackets). The brackets encoding
  62 --  method is ambiguous in the context of this package, since there is no way
  63 --  to tell if ["1234"] is eight unencoded characters or one encoded character.
  64 --  In the context of Ada sources, any sequence starting [" must be the start
  65 --  of an encoding (since that sequence is not valid in Ada source otherwise).
  66 --  The routines in this package use the same approach. If the input string
  67 --  contains the sequence [" then this is assumed to be the start of a brackets
  68 --  encoding sequence, and if it does not match the syntax, an error is raised.
  69 --  In the case of the Prev functions, a sequence ending with "] is assumed to
  70 --  be a valid brackets sequence, and an error is raised if it is not.
  71
  72 with System.WCh_Con;
  73
  74 generic
  75    Encoding_Method : System.WCh_Con.WC_Encoding_Method;
  76
  77 package GNAT.Decode_String is
  78    pragma Pure;
  79
  80    function Decode_Wide_String (S : String) return Wide_String;
  81    pragma Inline (Decode_Wide_String);
  82    --  Decode the given String, which is encoded using the indicated coding
  83    --  method, returning the corresponding decoded Wide_String value. If S
  84    --  contains a character code that cannot be represented with the given
  85    --  encoding, then Constraint_Error is raised.
  86
  87    procedure Decode_Wide_String
  88      (S      : String;
  89       Result : out Wide_String;
  90       Length : out Natural);
  91    --  Similar to the above function except that the result is stored in the
  92    --  given Wide_String variable Result, starting at Result (Result'First). On
  93    --  return, Length is set to the number of characters stored in Result. The
  94    --  caller must ensure that Result is long enough (an easy choice is to set
  95    --  the length equal to the S'Length, since decoding can never increase the
  96    --  string length). If the length of Result is insufficient Constraint_Error
  97    --  will be raised.
  98
  99    function Decode_Wide_Wide_String (S : String) return Wide_Wide_String;
 100    --  Same as above function but for Wide_Wide_String output
 101
 102    procedure Decode_Wide_Wide_String
 103      (S      : String;
 104       Result : out Wide_Wide_String;
 105       Length : out Natural);
 106    --  Same as above procedure, but for Wide_Wide_String output
 107
 108    function Validate_Wide_String (S : String) return Boolean;
 109    --  This function inspects the string S to determine if it contains only
 110    --  valid encodings corresponding to Wide_Character values using the
 111    --  given encoding. If a call to Decode_Wide_String (S) would return
 112    --  without raising Constraint_Error, then Validate_Wide_String will
 113    --  return True. If the call would have raised Constraint_Error, then
 114    --  Validate_Wide_String will return False.
 115
 116    function Validate_Wide_Wide_String (S : String) return Boolean;
 117    --  Similar to Validate_Wide_String, except that it succeeds if the string
 118    --  contains only encodings corresponding to Wide_Wide_Character values.
 119
 120    procedure Decode_Wide_Character
 121      (Input  : String;
 122       Ptr    : in out Natural;
 123       Result : out Wide_Character);
 124    pragma Inline (Decode_Wide_Character);
 125    --  This is a lower level procedure that decodes a single character using
 126    --  the given encoding method. The encoded character is stored in Input,
 127    --  starting at Input (Ptr). The resulting output character is stored in
 128    --  Result, and on return Ptr is updated past the input character or
 129    --  encoding sequence. Constraint_Error will be raised if the input has
 130    --  has a character that cannot be represented using the given encoding,
 131    --  or if Ptr is outside the bounds of the Input string.
 132
 133    procedure Decode_Wide_Wide_Character
 134      (Input  : String;
 135       Ptr    : in out Natural;
 136       Result : out Wide_Wide_Character);
 137    pragma Inline (Decode_Wide_Wide_Character);
 138    --  Same as above procedure but with Wide_Wide_Character input
 139
 140    procedure Next_Wide_Character (Input : String; Ptr : in out Natural);
 141    pragma Inline (Next_Wide_Character);
 142    --  This procedure examines the input string starting at Input (Ptr), and
 143    --  advances Ptr past one character in the encoded string, so that on return
 144    --  Ptr points to the next encoded character. Constraint_Error is raised if
 145    --  an invalid encoding is encountered, or the end of the string is reached
 146    --  or if Ptr is less than String'First on entry, or if the character
 147    --  skipped is not a valid Wide_Character code.
 148
 149    procedure Prev_Wide_Character (Input : String; Ptr : in out Natural);
 150    --  This procedure is similar to Next_Encoded_Character except that it moves
 151    --  backwards in the string, so that on return, Ptr is set to point to the
 152    --  previous encoded character. Constraint_Error is raised if the start of
 153    --  the string is encountered. It is valid for Ptr to be one past the end
 154    --  of the string for this call (in which case on return it will point to
 155    --  the last encoded character).
 156    --
 157    --  Note: it is not generally possible to do this function efficiently with
 158    --  all encodings, the current implementation is only efficient for the case
 159    --  of UTF-8 (Encoding_Method = WCEM_UTF8) and Brackets (Encoding_Method =
 160    --  WCEM_Brackets). For all other encodings, we work by starting at the
 161    --  beginning of the string and moving forward till Ptr is reached, which
 162    --  is correct but slow.
 163    --
 164    --  Note: this routine assumes that the sequence prior to Ptr is correctly
 165    --  encoded, it does not have a defined behavior if this is not the case.
 166
 167    procedure Next_Wide_Wide_Character (Input : String; Ptr : in out Natural);
 168    pragma Inline (Next_Wide_Wide_Character);
 169    --  Similar to Next_Wide_Character except that codes skipped must be valid
 170    --  Wide_Wide_Character codes.
 171
 172    procedure Prev_Wide_Wide_Character (Input : String; Ptr : in out Natural);
 173    --  Similar to Prev_Wide_Character except that codes skipped must be valid
 174    --  Wide_Wide_Character codes.
 175
 176 end GNAT.Decode_String;