This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 112c. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
The example in 9.4.3 [dcl.init.string] paragraph 1 says,
char msg = "Syntax error on line %s\n";
shows a character array whose members are initialized with a string-literal. Note that because '\n' is a single character and because a trailing '\0' is appended, sizeof(msg) is 25.
However, there appears to be no normative specification of how the size of the array is to be calculated.