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Volatile Variable in C?

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A.Rashad

A.Rashad

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What is Volatile Variable in C?
What is the role of Volatile variable in Embedded Application Programming?
Please Suggest Some Example code..
 

You can find many articles about this, for example

**broken link removed**
 

In case you are still struggling with it, here is a summary. Declare the variable as volatile if that variable can change its value outside of your C code. If you are certain that the variable is control entirely by the C code only and no hardware register or interrupt can modify it, then you dont need this "volatile" declaration.
 
what is a variable is shared by different modules of my code. In that case also do i need to declare that variable with volatile.

thanks
 

one example of the use in embedded application s is in interrupt service routines, e.g. usinga timer on a PIC24
Code: 
volatile long unsigned int mSecCounter=0; 	// counts millisecond interrupts

/* interrupt service routine for Timer1 ISR*/
void __attribute__((__interrupt__, __shadow__)) _T1Interrupt(void)
{
int i;
/* Interrupt Service Routine code goes here */
IFS0bits.T1IF = 0; 							//Reset Timer1 interrupt flag	
mSecCounter++;													
}
a modern compiler will optimize removing code that does not appear to do anything
volatile tells the compiler not to optimize references to variable mSecCounter, e.g.
Code: 
mSecCounter=0;
while(mSecCounter<1000) 
    ...;       // code executed for 1 second

- - - Updated - - -

akshada said:
what is a variable is shared by different modules of my code. In that case also do i need to declare that variable with volatile.

thanks
Click to expand...
no, you define in one module and declare it extern in other modules that use it
https://www.learncpp.com/cpp-tutorial/42-global-variables/
 

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