Question:

What is the use of volatile keyword in c++? Give an example.

Answer:

Most of the times compilers will do optimization to the code to speed up the program. For example in the below code,

int a = 10;
while( a == 10){
     // Do something
}

compiler may think that value of 'a' is not getting changed from the program and replace it with 'while(true)', which will result in an infinite loop. In actual scenario the value of 'a' may be getting updated from outside of the program.
Volatile keyword is used to tell compiler that the variable declared using volatile may be used from outside the current scope so that compiler wont apply any optimization. This matters only in case of multi-threaded applications.
In the above example if variable 'a' was declared using volatile, compiler will not optimize it. In shot, value of the volatile variables will be read from the memory location directly.


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