Wording for “Remove undefined behavior for mismatched quote characters”

Preamble

Contributors

Ryan Karl (rational, history)

Ryan Karl, Corentin Jabot, Jens Gustedt (wording)

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Wording choices

We avoid the ambiguity that was present in N3806 about ' characters that could appear in other constructs (in particular numbers) by insisting that the quote characters shall not be a single-character preprocessing token on their own.

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Close to each other proposed changes resemble like this.

Proposed wording

In 6.4.1 change

6.4 Lexical elements

6.4.1 General

…

2 Each preprocessing token that is converted to a token shall have the lexical form of a keyword, an identifier, a constant, a string literal, or a punctuator. A preprocessing token that consists of a single universal character name shall match one of the other preprocessing token categories. If a preprocessing token consists of a single character, that character shall not be a ' or " character.

Semantics

3 A token is the minimal lexical element of the language in translation phases 7 and 8 (5.2.1.2). The categories of tokens are: keywords, identifiers, constants, string literals, and punctuators. A preprocessing token is the minimal lexical element of the language in translation phases 3 through 6. The categories of preprocessing tokens are: header names, identifiers, preprocessing numbers, character literals, string literals, punctuators, and both single universal character names as well as single non-white-space characters that do not lexically match the other preprocessing token categories.⁴⁵⁾ If a ’ or a " character matches the last category, the behavior is undefined. Preprocessing tokens can be separated by white space; this consists of comments (described later), or white-space characters (space, horizontal tab, new-line, vertical tab, and form-feed), or both. As described in 6.10, in certain circumstances during translation phase 4, white space (or the absence thereof) serves as more than preprocessing token separation. White space may appear within a preprocessing token only as part of a header name or between the quotation characters in a character literal or string literal.

Remove from “J.2 Undefined behavior”

(19) An unmatched ’ or " character is encountered on a logical source line during tokenization (6.4).