Cpp - Read-Only References

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Introduction

A reference aliasing a constant object must be a constant itself.

It must be defined using the const keyword to avoid modifying the object by reference. 

int a;    
const int& cref = a;  // ok!

The reference cref can be used for read-only access to the variable a, and is said to be a read-only identifier.

A read-only identifier can be initialized by a constant, in contrast to a normal reference: 

const double& pi = 3.1415927;

Demo

// Demonstrates the definition and use of references. 
#include <iostream> 
#include <string> 
using namespace std; 

float x = 1.7F;        

int main() //ww  w  .  j a  va2 s  . c  om
{ 
   float  &rx = x;      // Local reference to x 
   rx *= 2; 

   const float& cref = x;     // Read-only reference 
   cout << "cref = " <<  cref << endl;  
   return 0; 
}

Result

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