Answer / satish

if a variable is declared as volatile ,optimization is not
done regarding to that variable.If the value is modified
many number of times,each time CPU goes and reads from main
memory rather than cache memory.
The usage of this can be
understood clearly only at kernel level but not at
application level.

Answer / babu

Declaraton an obj const announces that its value will not
be changed;declaring it Volatile announces that it has
special properties relevent to optimization[change].

Answer / agung bakhtiar

A volatile variable is the one whose values may be changed at any time by some external sources

Answer / shenbagavalli

The volatile keyword is a type qualifier used to declare
that an object can be modified in the program by something
such as the operating system, the hardware, or a
concurrently executing thread.

Answer / chandrashekar kalvacherla

volatile tells the compiler that this variable can get altered by ways that the compiler cannot deduce. As a consequence, the compiler will exclude that variable from optimizations and the code will always fetch the variables content from memory, even if it has done so before (no caching).

Imagine a hardware clock which is mapped into memory. You need some way to tell the compiler: whenever I access that variable (mapped to the hardware clock), I want you to actually fetch the content from there. Otherwise the compiler might just ask the clock once for the current time and use the cached value (in a processor register) throught the rest of the program.

Answer / srividya

A volatile variable is variable whose value can change with
out the knowledge of the compile. so the data access
optimization is lost.
These sort of variable are used normally accessing a global
variable between two threads.

Answer / vivek satasia

IT IS SUCH A VARIABLE WHICH IS NOT MODIFIED BY ITS PROGRAM
BUT IT CAN BE MODIFIED OUTSIDE PROGRAM ENVIRONMENT.

Answer / priya

In computer programming,a variable or object declared
with the volatile keyword may be modified externally
from the declaring object. Variables declared to be
volatile will not be optimized by the compiler
because the compiler must assume that their values
can change at any time.

Answer / vinod

the variable which can be modify

Answer / vishal

What is the significance of volatile keyword?
Volatile keyword is used to inform the compiler not to predict/assume/believe/presume the value of the particular variable which has been declared as volatile.



Why/When do we need volatile ?
In following case we need to use volatile variable.




Memory-mapped peripheral registers
Global variables modified by an interrupt service routine
Global variables within a multi-threaded application
If we do not use volatile qualifier the following problems may arise:




Code that works fine-until you turn optimization on
Code that works fine-as long as interrupts are disabled
Flaky hardware drivers
Tasks that work fine in isolation-yet crash when another task is enabled

Source: http://www.firmcodes.com/volatile-keyword-in-c-and-embedded-system/

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