volatile const

[Rahul]

Hi Everyone,

The following code compiles without any error,

int main()
{
volatile const int a = 10;
return(0);
};

But i expected a compilation error as a is being told as a constant
and at the same time indicating that its value could change outside
the program's control...

Why isn't this an error?

Thanks in advance ! ! !

 

[Andrey Tarasevich]

The following code compiles without any error,

int main()
{
volatile const int a = 10;
return(0);
};

But i expected a compilation error as a is being told as a constant
and at the same time indicating that its value could change outside
the program's control...

Why isn't this an error?

Why should it be an error? This is exactly what 'volatile const' is
supposed to mean in the first place: the program is not allowed to
change the object, but its value can change "by itself".

 

[Richard Bos]

int main()
{
volatile const int a = 10;
return(0);
};

But i expected a compilation error as a is being told as a constant

No, it's being declared as something _you_ won't change.

and at the same time indicating that its value could change outside
the program's control...

Quite. It is something your code won't change, but something else will.
One example of this could be a hardware counter, or an input port.

Richard

 

[Joachim Schmitz]

Hi Everyone,

The following code compiles without any error,

int main()
{
volatile const int a = 10;
return(0);
};

But i expected a compilation error as a is being told as a constant
and at the same time indicating that its value could change outside
the program's control...

Why isn't this an error?

Because for some stupid reason in C const doesn't mean 'constant' but 'read
only'

Bye,Jojo

 

[Richard Tobin]

volatile const int a = 10;

[/QUOTE]

Why should it be an error? This is exactly what 'volatile const' is
supposed to mean in the first place: the program is not allowed to
change the object, but its value can change "by itself".

The standard gives this example:

extern const volatile int real_time_clock;

You can't change the time, but it changes anyway.

-- Richard

 

[raof01]

Hello Joachim,

Because for some stupid reason in C const doesn't mean 'constant' but
'read only'

Yes, absolutely. Furthermore, "const" means read only JUST for you. On the
other hand, "volatile" doesn't mean you can modify it but you HAVE TO reload
it from memory every time you use it. "volatile" is more like an indicator
for compiler to protect from optimizing.

raof01
"Thoughts are but dreams till their effects be tried. -- William Shakespeare"