Q94 What is volatile variable in C? Where we use volatile variable?

volatile variable in c

Volatile is a qualifier that is applied to a variable when it is declared. It tells the compiler that the value of the variable may change at any time-without any action being taken by the code the compiler finds nearby. Variables declared as volatile are omitted from optimization because their values can be changed by code outside the scope of current code at any time. The system always reads the current value of a volatile object from the memory location rather than keeping its value in temporary register at the point it is requested, even if a previous instruction asked for a value from the same variable.

To declare a variable volatile, include the keyword volatile before or after the data type in the variable definition. For instance both of these declarations will declare foo to be a volatile integer:

volatile int var;
int volatile var;

Use of volatile variables

  1. Memory-mapped peripheral registers
  2. Global variables modified by an interrupt service routine
  3. Global variables within a multi-threaded application

 

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