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C Compiler
2.8
Implementation Details
This section gives details of those aspects of the compiler and C library which the ANSI standard
for C identifies as implementation-defined, together with other points of interest to programmers.
2.8.1
Character sets and identifiers
An identifier can be of any length. The compiler truncates an identifier after 256 characters, all
of which are significant (the standard requires a minimum of 31 significant characters).
The source character set expected by the compiler is 7-bit ASCII. Within comments, string
literals, and character constants, the full ISO 8859-1 (Latin 1) 8-bit character set is recognised.
In its generic configuration, as delivered, the C library processes the full ISO 8859-1 (Latin-1)
8-bit character set, except that the default locale is the C locale (see ➲Standard Implementation
Definition on page 2-24). The ctype functions therefore all return 0 when applied to codes in
the range 160 to 255.
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 7-bit ASCII
subset.
Upper and lower case characters are distinct in all internal and external identifiers.
In pcc mode (-pcc option) and “limited pcc” or “system programming” mode (-fc option), an
identifier may also contain a dollar character.
2.8.2
Data Elements
Type
Size in bits
Type
Size in bits
char
8
float
32
short
16
double
64
int
32
long double
64 (subject to change)
long
32
all pointers
32
Table 2-1: Size of data elements
Integers are represented in two’s complement form.
Data items of type char are unsigned by default, though in ANSI mode they may be explicitly
declared as signed char or unsigned char.
In the compiler’s pcc mode there is no signed keyword, so chars are signed by default and
may be declared unsigned if required.
Reference Manual
ARM DUI 0020D
2-17