This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 115d. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-10-26

1103. Reversion of phase 1 and 2 transformations in raw string literals

[Voted into the WP at the November, 2010 meeting.]

“Raw” strings are still only Pittsburgh-rare strings: the reversion in phase 3 only applies to an r-char-sequence. It should apply to the entire raw string literal.

Proposed resolution (August, 2010):

1. Change 5.2 [lex.phases] paragraph 1 phase 1 as follows:

...(An implementation may use any internal encoding, so long as an actual extended character encountered in the source file, and the same extended character expressed in the source file as a universal-character-name (i.e., using the \uXXXX notation), are handled equivalently except where this replacement is reverted in a raw string literal.).)

2. Change 5.2 [lex.phases] paragraph 1 phase 3 as follows:

...[Example: see the handling of < within a #include preprocessing directive. —end example] Within the r-char-sequence of a raw string literal, any transformations performed in phases 1 and 2 (trigraphs, universal-character-names, and line splicing) are reverted.

3. Change 5.2 [lex.phases] paragraph 1 phase 5 as follows:

Each source character set member and universal-character-name in a character literal or a string literal, as well as each escape sequence and universal-character-name in a character literal or a non-raw string literal, is converted to the corresponding member of the execution character set (5.13.3 [lex.ccon], 5.13.5 [lex.string]); if there is no corresponding member, it is converted to an implementation-defined member other than the null (wide) character.

4. Change 5.3 [lex.charset] paragraph 2 as follows:

...Additionally, if the hexadecimal value for a universal-character-name outside the c-char-sequence, s-char-sequence, or r-char-sequence of a character or string literal corresponds to a control character (in either of the ranges 0x000x1F or 0x7F0x9F, both inclusive) or to a character in the basic source character set, the program is ill-formed. [Footnote: A sequence of characters resembling a universal-character-name in an r-char-sequence (5.13.5 [lex.string]) does not form a universal-character-name. —end footnote]

5. Change 5.4 [lex.pptoken] paragraph 3 as follows:

If the input stream has been parsed into preprocessing tokens up to a given character:

• if If the next character begins a sequence of characters that could be the prefix and initial double quote of a raw string literal, such as R", the next preprocessing token shall be a raw string literal;. Between the initial and final double quote characters of the raw string, any transformations performed in phases 1 and 2 (trigraphs, universal-character-names, and line splicing) are reverted; this reversion shall apply before any d-char, r-char, or delimiting parenthesis is identified. The raw string literal is defined as the shortest sequence of characters that matches the raw-string pattern

encoding-prefix_opt R raw-string

• otherwise Otherwise, the next preprocessing token is the longest sequence of characters that could constitute a preprocessing token, even if that would cause further lexical analysis to fail.

6. Delete footnote 24 in 5.13.5 [lex.string] paragraph 2:

Use of characters with trigraph equivalents in a d-char-sequence may produce unintended results.

7. Insert the following examples after 5.13.5 [lex.string] paragraph 4:

[Example: The raw string

  R"a(
  )\
  a"
  )a"

is equivalent to "\n)\\\na\"\n". The raw string

  R"(??)"

is equivalent to "\?\?". The raw string

  R"#(
  )??="
  )#"

is equivalent to "\n)\?\?=\"\n". —end example]