Describes implementation-defined aspects of the ARM C compiler and C library relating to characters, as required by the ISO C standard.
The following points apply to the character sets expected by the compiler:
setlocale(LC_CTYPE, "ISO8859-1")makes the
islower()functions behave as expected over the full 8-bit Latin-1 alphabet, rather than over the 7-bit ASCII subset. The locale must be selected at link time.
Source files are compiled according to the currently selected locale. You might have to change the locale using the
--localecommand-line option if the source file contains non-ASCII characters. If you do not specify
--locale, the system locale is used.
The compiler supports multibyte character sets, such as Unicode. You can control this support using the
If the source file encoding is UTF-8 or UTF-16, and the file starts with a byte order mark then the compiler ignores the
--localeoptions and interprets the file as UTF-8 or UTF-16.
Other properties of the source character set are host-specific.
The properties of the execution character set are target-specific. The ARM® C and C++ libraries support the ISO 8859-1 (Latin-1 Alphabet) character set with the following consequences:
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:
The bytes are ordered from least significant at the lowest address to most significant at the highest address.
The bytes are ordered from least significant at the highest address to most significant at the lowest address.
In C all character constants have type
int. In C++ a character constant containing one character has the type
charand 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
All integer character constants that contain a single character, or character escape sequence, are represented in both the source and execution character sets.The following table lists the supported character escape codes.
Table 15-1 Character escape codes
Escape sequence Char value Description
New line (line feed)
ASCII code in hexadecimal
ASCII code in octal
Characters of the source character set in string literals and character constants map identically into the execution character set.
Data items of type
charare unsigned by default. They can be explicitly declared as
--signed_charsoption makes the
--unsigned_charsoption makes the
Care must be taken when mixing translation units that have been compiled with and without the
--unsigned_charsoptions, and that share interfaces or data structures.
The ARM ABI defines
charas an unsigned byte, and this is the interpretation used by the C++ libraries supplied with the ARM compilation tools.
Converting multibyte characters into the corresponding wide characters for a wide character constant does not use a locale. This is not relevant to the generic implementation.