Can a volatile variable be const?

Yes a C++ variable be both const and volatile. It is used in situations like a read-only hardware register, or an output of another thread. Volatile means it may be changed by something external to the current thread and Const means that you do not write to it (in that program that is using the const declaration).

What is the use of const volatile?

The const keyword specifies that the pointer cannot be modified after initialization; the pointer is protected from modification thereafter. The volatile keyword specifies that the value associated with the name that follows can be modified by actions other than those in the user application.

Where are const volatile variables used?

We use ‘const’ keyword for a variable when we don’t want to the program to change it. Whereas when we declare a variable ‘const volatile’ we are telling the program not to change it and the compiler that this variable can be changed unexpectedly from input coming from the outside world.

Can you have constant volatile variable Yes you can have a volatile pointer?

Yes, a pointer can be volatile if the variable that it points to can change unexpectedly even though how this might happen is not evident from the code.

Is const opposite of volatile?

(A) const is the opposite of volatile and vice versa. (B) const and volatile can’t be used for struct and union. (C) const and volatile can’t be used for enum. (D) const and volatile can’t be used for typedef.

What is the difference between const int and int const?

So in your question, “int const *” means that the int is constant, while “int * const” would mean that the pointer is constant. If someone decides to put it at the very front (eg: “const int *”), as a special exception in that case it applies to the thing after it.

What is volatile int?

int or long volatiles

This means that while your main code section (e.g. your loop) reads the first 8 bits of the variable, the interrupt might already change the second 8 bits. This will produce random values for the variable.

Can a parameter be both const and volatile in C?

Yes, it is possible. The best example is Status Register in controllers, in the program we should not modify this Status Register so it should be a constant.

Can a variable be both const and volatile in C example?

Can we use const int in C?

int const *ptr; We can change the pointer to point to any other integer variable, but cannot change the value of the object (entity) pointed using pointer ptr. The pointer is stored in the read-write area (stack in the present case).

What is meant by const int?

int const* is pointer to constant integer This means that the variable being declared is a pointer, pointing to a constant integer. Effectively, this implies that the pointer is pointing to a value that shouldn’t be changed.

Is volatile thread safe?

Therefore, the volatile keyword does not provide thread safety when non-atomic operations or composite operations are performed on shared variables. Operations like increment and decrement are composite operations.

What is const and volatile qualifier?

What is the difference between const int and const int?

const int * And int const * are the same. const int * const And int const * const are the same. If you ever face confusion in reading such symbols, remember the Spiral rule: Start from the name of the variable and move clockwise to the next pointer or type.

What does const int do in C?

const int* const says that the pointer can point to a constant int and value of int pointed by this pointer cannot be changed. And we cannot change the value of pointer as well it is now constant and it cannot point to another constant int.

What is the difference between int and const int?

The int is basically the type of integer type data. And const is used to make something constant. If there is int& constant, then it indicates that this will hold the reference of some int type data. This reference value is constant itself.

Why volatile is used in Singleton?

The volatile prevents memory writes from being re-ordered, making it impossible for other threads to read uninitialized fields of your singleton through the singleton’s pointer.

Should I use volatile with synchronized?

When to use Volatile over Synchronized modifiers can be summed up into this: Use Volatile when you variables are going to get read by multiple threads, but written to by only one thread. Use Synchronized when your variables will get read and written to by multiple threads.

What does const int mean?

pointer to constant integer
int const* is pointer to constant integer This means that the variable being declared is a pointer, pointing to a constant integer. Effectively, this implies that the pointer is pointing to a value that shouldn’t be changed.

Is volatile required in Singleton?

Without volatile the code doesn’t work correctly with multiple threads. From Wikipedia’s Double-checked locking: As of J2SE 5.0, this problem has been fixed. The volatile keyword now ensures that multiple threads handle the singleton instance correctly.

What is the difference between volatile and synchronized?

We can solve this problem by using a volatile modifier. If a variable is declared as volatile as for every thread JVM will create a separate local copy.

Output.

Synchronized Volatile Atomic
1.It is applicable to only blocks or methods. 1.It is applicable to variables only. 1.It is also applicable to variables only.

Do we need volatile in synchronized block?

It’s not a necessary to use volatile variable in it… volatile updates the one variable from main memory..and synchronized Update all shared variables that have been accessed from main memory.. So you can use it according to your requirement..

What is the difference between int const and const int?

The general rule is that the const keyword applies to what precedes it immediately. Exception, a starting const applies to what follows. const int* is the same as int const* and means “pointer to constant int”. const int* const is the same as int const* const and means “constant pointer to constant int”.

Why singleton is not thread safe?

Is singleton thread safe? A singleton class itself is not thread safe. Multiple threads can access the singleton same time and create multiple objects, violating the singleton concept. The singleton may also return a reference to a partially initialized object.

Why singleton instance is volatile?