This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 116a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2024-12-19
Subclause 15.12 [cpp.pragma.op] paragraph 1 specifies:
A unary operator expression of the form:
_Pragma ( string-literal )
is processed as follows: The string-literal is destringized by
deleting the L prefix, if present, deleting the leading and
trailing double-quotes, replacing each escape sequence \" by
a double-quote, and replacing each escape sequence \\ by a
single backslash. The resulting sequence of characters is processed
through translation phase 3 to produce preprocessing tokens that are
executed as if they were the pp-tokens in a pragma directive.
The original four preprocessing tokens in the unary operator
expression are removed.
In contrast, C23 section 6.10.6 specifies:
A unary operator expression of the form:
_Pragma ( string-literal )
is processed as follows: The string literal is destringized by deleting
any encoding prefix, ...
While in C, any encoding prefix is deleted, C++ only deletes the L prefix and does not consider UTF-8, UTF-16, and UTF-32 string literals. This was probably an oversight when C++ obtained UTF-x string literals.
However, a string-literal entails lexing of escape sequences and universal-character-names, which seems not useful given that the string literal is de-stringized immediately afterwards. It might be more appropriate to employ a simpler lexical structure such as a q-char-sequence as used in a header-name instead. See also issue 2693.
See also issue 897, which is also concerned with raw string literals and line splicing.