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The C++ sizeof() operator returns the size of data type, constants, variable. It is a compile-time operator as it returns the size of any variable or a constant at the compilation time. It can also be used to get the size of classes, structures, unions and any other user defined data type.


//returns the size in bytes of the 
//object representation of type.

//returns the size in bytes of the object 
//representation of the type of expression, 
//if the expression is evaluated.
sizeof expression

Return Value

Returns the size in bytes of the object representation of type or type of expression.


The below example shows the usage of sizeof() operator.

#include <iostream>
using namespace std;

int main (){
  int x = 10;
  int A[10];
  int * ptr;
  ptr = A;

  //displaying size in bytes of 
  //various object representation 
  cout<<"Size of int : "<<sizeof(int)<<"\n";
  cout<<"Size of float : "<<sizeof(float)<<"\n";
  cout<<"Size of double : "<<sizeof(double)<<"\n";
  cout<<"Size of long double : "<<sizeof(long double)<<"\n";  
  cout<<"Size of variable x : "<<sizeof(x)<<"\n";
  cout<<"Size of array A : "<<sizeof A<<"\n";
  cout<<"Size of pointer ptr : "<<sizeof &ptr<<"\n";

  return 0;

The output of the above code will be:

Size of int : 4
Size of float : 4
Size of double : 8
Size of long double : 16
Size of variable x : 4
Size of array A : 40
Size of pointer ptr : 8

❮ C++ - Operators