ARM VERSION 1.2 Datasheet download pdf (Page 75)

ARM Compiler Reference

Hexadecimal floating-point constants

ARM implements an extension to the syntax of numeric constants in C to enable explicit

specification of floating-point constants as IEEE bit patterns. The syntax is:

0f_n

Interpret an 8-digit hex number n as a

float

0d_nn

Interpret a 16-digit hex number nn as a

double

There must be exactly eight digits for

float

constants. There must be exactly 16 digits

for

double

constants.

Read/write constants

For C++ only, a linkage specification for external constants indicates that a constant can

be dynamically initialized or have mutable members.

Note

The use of

"C++:read/write"

linkage is only necessary for code compiled

/ropi

/rwpi

If you recompile existing code with either of these options, you must change the linkage

specification for external constants that are dynamically initialized or have mutable

members.

Compiling C++ with either the

/ropi

/rwpi

options deviates from the C++ standard.

The declarations in Example 3-5 assume that

is in a read-only segment.

Example 3-5 External access

extern const T x;

extern "C++" const T x;

extern "C" const T x;

Dynamic initialization of

(including user-defined constructors) is not possible for the

constants and

cannot contain mutable members. The new linkage specification in

Example 3-6 on page 3-20 declares that

is in a read/write segment (even if it was

initialized with a constant). Dynamic initialization of

is allowed and

can contain

mutable members. The definitions of

, and

in another file must have the same

linkage specifications.

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ARM VERSION 1.2 Datasheet Page 75

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