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Introduction Compiler Command-line Options Language Extensions Compiler-specific Features 
C and C++ Implementation Details C and C++ implementation details Character sets and identifiers Basic data types Operations on basic data types Structures, unions, enumerations, and bitfields C++ implementation details Using the ::operator new function Tentative arrays Old-style C parameters in C++ functions Anachronisms Template instantiation Namespaces C++ exception handling Extern inline functions ARMv6 SIMD Instruction Intrinsics Via File Syntax Summary Table of GNU Language Extensions Standard C Implementation Definition Standard C++ Implementation Definition C and C++ Compiler Implementation LimitsCharacter sets and identifiers
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The following points apply to the character sets and identifiers expected by the compiler:
Uppercase and lowercase characters are distinct in all internal and external identifiers. An identifier can also contain a dollar
($)character unless the--strictcompiler option is specified. To permit dollar signs in identifiers with the--strictoption, also use the--dollarcommand-line option.Calling
setlocale(LC_CTYPE, "ISO8859-1")makes theisupper()andislower()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 select a different locale, with the
--localecommand-line option, if the source file contains non-ASCII characters. See Compiler command-line options listed by group in Using the Compiler for more information.The compiler supports multibyte character sets, such as Unicode.
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:
- Little-endian
The bytes are ordered from least significant at the lowest address to most significant at the highest address.
- Big-endian
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 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.Table 30 lists all integer character constants, that contain a single character or character escape sequence, are represented in both the source and execution character sets.
Table 30. Character escape codes
Escape sequence Char value Description \a7Attention (bell) \b8Backspace \t9Horizontal tab \n10New line (line feed) \v11Vertical tab \f12Form feed \r13Carriage return \xnn0xnnASCII code in hexadecimal \nnn0nnnASCII 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 char are unsigned by default. They can be explicitly declared as signed char or unsigned char:
the
--signed_charsoption can be used to make the char signedthe
--unsigned_charsoption can be used to make the char unsigned.
Note
Care must be taken when mixing translation units that have been compiled with and without the
--signed_charsand--unsigned_charsoptions, and that share interfaces or data structures.The ARM ABI defines char as an unsigned byte, and this is the interpretation used by the C++ libraries supplied with the ARM compilation tools.
No locale is used to convert multibyte characters into the corresponding wide characters for a wide character constant. This is not relevant to the generic implementation.
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