The number of bits in a byte (C90 3.4, C99 and C11 3.6). Determined by ABI.
The values of the members of the execution character set (C90, C99 and C11 5.2.1). Determined by ABI.
The unique value of the member of the execution character set produced for each of the standard alphabetic escape sequences (C90, C99 and C11 5.2.2). Determined by ABI.
The value of a char object into which has been stored any character other than a member of the basic execution character set (C90 6.1.2.5, C99 and C11 6.2.5). Determined by ABI.
Which of signed char or unsigned char has the same range, representation, and behavior as “plain” char (C90 6.1.2.5, C90 6.2.1.1, C99 and C11 6.2.5, C99 and C11 6.3.1.1). Determined by ABI. The options -funsigned-char and-fsigned-char change the default. See Options Controlling C Dialect.
The mapping of members of the source character set (in character constants and string literals) to members of the execution character set (C90 6.1.3.4, C99 and C11 6.4.4.4, C90, C99 and C11 5.1.1.2). Determined by ABI.
The value of an integer character constant containing more than one character or containing a character or escape sequence that does not map to a single-byte execution character (C90 6.1.3.4, C99 and C11 6.4.4.4). See Implementation-defined behavior in The C Preprocessor.
The value of a wide character constant containing more than one multibyte character or a single multibyte character that maps to multiple members of the extended execution character set, or containing a multibyte character or escape sequence not represented in the extended execution character set (C90 6.1.3.4, C99 and C11 6.4.4.4). See Implementation-defined behavior in The C Preprocessor.
The current locale used to convert a wide character constant consisting of a single multibyte character that maps to a member of the extended execution character set into a corresponding wide character code (C90 6.1.3.4, C99 and C11 6.4.4.4). See Implementation-defined behavior in The C Preprocessor.
Whether differently-prefixed wide string literal tokens can be concatenated and, if so, the treatment of the resulting multibyte character sequence (C11 6.4.5). Such tokens may not be concatenated.
The current locale used to convert a wide string literal into corresponding wide character codes (C90 6.1.4, C99 and C11 6.4.5). See Implementation-defined behavior in The C Preprocessor.
The value of a string literal containing a multibyte character or escape sequence not represented in the execution character set (C90 6.1.4, C99 and C11 6.4.5). See Implementation-defined behavior in The C Preprocessor.
The encoding of any of wchar_t, char16_t, andchar32_t where the corresponding standard encoding macro (__STDC_ISO_10646__, __STDC_UTF_16__, or__STDC_UTF_32__) is not defined (C11 6.10.8.2). See Implementation-defined behavior in The C Preprocessor. char16_t andchar32_t literals are always encoded in UTF-16 and UTF-32 respectively.