Datasheet

ARM Compiler Reference

3.3.2 Basic data types

This section gives information about how the basic data types are implemented in ARM

C and C++.

Size and alignment of basic data types

Table 3-3 gives the size and natural alignment of the basic data types. Type alignment

varies according to the context. (See Structures, unions, enumerations, and bitfields on

page 3-26.)

• Local variables are usually kept in registers, but when local variables are spilled

onto the stack, they are always word-aligned. For example, a spilled local

char

variable has an alignment of 4.

• The natural alignment of a packed type is 1.

Integer

Integers are represented in two's complement form. The low word of a

long long

is at

the low address in little-endian mode, and at the high address in big-endian mode.

Table 3-3 Size and alignment of data types

Type Size in bits Natural alignment in bytes

char

8 1 (byte-aligned)

short

16 2 (halfword-aligned)

int

32 4 (word-aligned)

long

32 4 (word-aligned)

long long

64 4 (word-aligned)

float

32 4 (word-aligned)

double

64 4 (word-aligned)

long

double

64 4 (word-aligned)

All pointers 32 4 (word-aligned)

bool

(C++ only) 32 4 (word-aligned)