Re: FW: (unknown)

That's not a good example.  Any function can have arbitrary side effects.
For example, your function which reads port data might update some
static variables.   This optimization would not actually be done by a
compiler.  Consider if you have a void function foo() called three times:

   foo();
   foo();
   foo();

You are telling me that this would be not be optimized whereas this
would?
   x = foo();
   x = foo();
   x = foo();

The examples I've seen with volatile always involved pointers.

At 10:40 PM 11/17/2003 +0800, you wrote:

>Hi,
>
>I'll try to give an example that I had read long time back. Suppose I
>have the following:
>
>int x = get 2 bytes from some port;
>x = get next 2 bytes from same port;
>
>Now in the above situation, since the port is same, compiler will assume
>the the 2 statements to be identical and optimise by deleting the second
>line, thinking it to be a repeat of the first.
>
>This is unacceptable obviously. Thus if the variable 'x' was marked as
>volatile, such optimizations won't be performed and the 2 lines remain
>intact.
>
>Hope this helps :)
>
>Regards,
>
>Saikat
>
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>
>-----Original Message-----
>From: Viking >:) [mailto:[email protected]] 
>Sent: Monday, November 17, 2003 2:40 PM
>To: [email protected]
>Subject: [cppug] (unknown)
>
>
>Hello Group,
>
>I am a new member to this group. 
>
>Can any one please explain me about the volatile keyword.  According 
>Mr.StrousStrup in "The C++ Programming Language"  the definition is 
>as follows.
>
>"A Volatile specifier is a hint to the Compiler that an object my 
>change its value in ways not specified by the language, so aggressive 
>optimizations to be avoided."
>
>
>My doubts are 
>
>"an object my change its value in ways not specified by the language"
>
>1) What is this ? How will an object change  its ways in ways not 
>specified by the language ? 
>
>If some example is given about this , that would be greatful.
>
>"so aggressive optimizations to be avoided."
>
>2) Who does optimizations ? Compiler ? Does it does it automatically 
>or by Specifing some switches...?
>
>
>Thanks in Advance.
>
>Cheers,
>Blue Viking
>
>
>
>
>
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