Zilog Z8F0130 - Manual (Page 280)

Using the ANSI C-Compiler UM013037-1212
256
Zilog Developer Studio II – Z8 Encore!
User Manual
extensions that are useful for developing embedded applications and for making efficient
use of the resources of the Z8 Encore! CPU. These extensions are described in the
Lan-
guage Extensions section on page 194.
Deviations from ANSI C
The differences between the Zilog Z8 Encore! C-Compiler and the freestanding imple-
mentation of ANSI C Standard consist of both extensions to the ANSI standard and devia-
tions from the behavior described by the standard. The extensions to the ANSI standard
are explained in the
Language Extensions section on page 194.
There are a small number of areas in which the Z8 Encore! C-Compiler does not behave as
specified by the standard. These areas are described in the following sections:
•
Prototype of Main – see page 256
•
Double Treated as Float – see page 257
•
const Keyword and ROM – see page 257
•
Const Correctness in the Standard Header Files – see page 258
•
ANSI Promotions Disabled – see page 258
•
Library Files Not Required for Freestanding Implementation – see page 258
Prototype of Main
As per ANSI C, in a freestanding environment, the name and type of the function called at
program start-up are implementation defined. Also, the effect of program termination is
implementation defined.
For compatibility with hosted applications, the Z8 Encore! C-Compiler uses main() as
the function called at program startup. Because the Z8 Encore! compiler provides a free-
standing execution environment, there are a few differences in the syntax for
main() . The
most important of these is that, in a typical small embedded application, main() never
executes a return because there is no operating system for a value to be returned to and it is
also not intended to terminate. If
main() does terminate and the standard Zilog Z8
Encore! C start-up module is in use, control simply goes to the following statement:
_exit:

JR _exit
For this reason, in the Z8 Encore! C-Compiler, main() must be of type void ; any
returned value is ignored. Also, main() is not passed any arguments. In short, the follow-
ing is the prototype for main() :
void main (void);
Unlike the hosted environment in which the closest allowed form for main is as follows:
int main (void);