RE: [avr-gcc-list] (no subject)

[Dave Hansen]

From: "MuRaT KaRaDeNiZ" <address@hidden>
> So
>
> U08 RX485_oldbyte1; is uninitialized data, but compiler also initialize
> it to zero, why is it different from inline initialization during
> declaration, I expect the compiler just replace the zero with the
> initial value i provide?

Because reality is different than what you expect.

In C, there are really two kinds of declarations, those that define the 
object, and those that reference it.  Rule number 1: There may be only 1 
defining declaration in a program.

How do you tell the difference?  If a declaration includes an initializer, 
it is a (the) defining declaration.

If none of the declarations of an object include an initializer, then all 
referencing declarations must be declared with the extern storage class.

A top-level declaration without extern and without an initializer is called 
a tentative definition.  It is treated as a referencing declaration, but if 
no other declaration of the variable in the file includes an initializer, 
then the tentative definition becomes a defining declaration.

If an implementation permits tentative declarations in multiple translation 
units without issuing a diagnostic, it is non-conforming, but supports a 
common extension.  Avoid taking advantage of this extensionif you want your 
code to be portable.

HTH,
  -=Dave