The execution character set is the implementation-defined mapping used to represent characters while a C program runs. Numeric character encodings therefore depend on the platform and the particular execution setting. section 8.5
Numeric escapes in strings
Do not assume that "\xdeBruyn" means a character encoded by \xde followed by "Bruyn". The hexadecimal escape consumes every following hexadecimal digit, so it can become one character with code 3,563 followed by "ruyn". Writing "\xde""Bruyn" ends the escape before the next text. Whether code 3,563 exists, and which character it represents, depends on the execution character set. section 8.5
Keep these portability rules in mind:
- Treat numerically encoded characters as non-portable unless the required character exists with the intended representation. section 8.5
- Use character classification functions carefully: implementations may extend classes with platform-specific characters. section 8.5
Table 8.14 Character classifiers. The third column indicates whether C implementations may extend these classes with platform-specific characters, such as ’ ä’ as a lowercase character or ’ €’ as punctuation.
| Name | Meaning | C locale | Extended |
islower |
Lowercase | ’a’ ⋯ ’z’ |
Yes |
isupper |
Uppercase | ’A’ ⋯ ’Z’ |
Yes |
isblank |
Blank | ’ ’, ’'͡ |
Yes |
isspace |
Space | ”, ’'̑, ’’, ’'̊, ’'͡, ’'̌ |
Yes |
isdigit |
Decimal | ’0’ ⋯ ’9’ |
No |
isxdigit |
Hexadecimal | ’0’ ⋯ ’9’, ’a’ ⋯ ’f’, ’A’ ⋯ ’F’ |
No |
iscntrl |
Control | ’’, ’'̱, ’'̑, ’’, ’'̊, ’'͡, ’'̌ |
Yes |
isalnum |
Alphanumeric | isalpha(x)||isdigit(x) |
Yes |
isalpha |
Alphabet | islower(x)||isupper(x) |
Yes |
isgraph |
Graphical | (!iscntrl(x)) && (x != ”) |
Yes |
isprint |
Printable | !iscntrl(x) |
Yes |
ispunct |
Punctuation | isprint(x)&&!(isalnum(x)||isspace(x)) |
Yes |
Compare standard character classes with implementation-defined extensions, including possible additional lowercase or punctuation characters. section 8.5
