Uppercase and lowercase characters are distinct in all internal and external identifiers. An identifier can also contain a dollar ($) character unless the --strict compiler option is specified. To permit dollar signs in identifiers with the --strict option, then also use the --dollar command-line option.

Calling setlocale(LC_CTYPE, "ISO8859-1") makes the isupper() and islower() functions behave as expected over the full 8-bit Latin-1 alphabet, rather than over the seven-bit ASCII subset. The locale must be selected at link-time. (See Tailoring locale and CTYPE.)

The characters in the source character set are assumed to be ISO 8859-1 (Latin-1 Alphabet), a superset of the ASCII character set. The printable characters are those in the range 32 to 126 and 160 to 255. Any printable character can appear in a string or character constant, and in a comment.

The ARM compiler supports multibyte character sets, such as Unicode.

Other properties of the source character set are host-specific.

The execution character set is identical to the source character set.

There are eight bits in a character in the execution character set.

There are four characters (bytes) in an int. If the memory system is:

In C all character constants have type int. In C++ a character constant containing one character has the type char and a character constant containing more than one character has the type int. Up to four characters of the constant are represented in the integer value. The last character in the constant occupies the lowest-order byte of the integer value. Up to three preceding characters are placed at higher-order bytes. Unused bytes are filled with the NULL (\0) character.

All integer character constants that contain a single character, or character escape sequence (see Table 3.2), are represented in both the source and execution character sets.

Characters of the source character set in string literals and character constants map identically into the execution character set.

Data items of type char are unsigned by default. They can be explicitly declared as signed char or unsigned char:

No locale is used to convert multibyte characters into the corresponding wide characters (codes) for a wide character constant. This is not relevant to the generic implementation.