Passing Reference to a Pointer in C++
Last Updated :
11 Jul, 2025
Prerequisite:
Pointers vs References in C++.
For clear understanding, let's compare the usage of a "pointer to pointer" VS "Reference to pointer" in some cases.
Note: It is allowed to use "pointer to pointer" in both C and C++, but we can use "Reference to pointer" only in C++.
Passing pointer to a function
If a pointer is passed to a function as a parameter and tried to be modified then the changes made to the pointer does not reflects back outside that function. This is because only a copy of the pointer is passed to the function. It can be said that "pass by pointer" is
passing a pointer by value. In most cases, this does not present a problem. But the problem comes when you modify the pointer inside the function. Instead of modifying the variable, you are only modifying a copy of the pointer and the original pointer remains unmodified.
Below program illustrate this:
CPP
#include <iostream>
using namespace std;
int global_Var = 42;
// function to change pointer value
void changePointerValue(int* pp)
{
pp = &global_Var;
}
int main()
{
int var = 23;
int* ptr_to_var = &var;
cout << "Passing Pointer to function:" << endl;
cout << "Before :" << *ptr_to_var << endl; // display 23
changePointerValue(ptr_to_var);
cout << "After :" << *ptr_to_var << endl; // display 23
return 0;
}
Output:
Passing Pointer to function:
Before :23
After :23
Passing "pointer to a pointer" as a parameter to function
The above problem can be resolved by passing the address of the pointer to the function instead of a copy of the actual function. For this, the function parameter should accept a "pointer to pointer" as shown in the below program:
CPP
#include <iostream>
using namespace std;
int global_var = 42;
// function to change pointer to pointer value
void changePointerValue(int** ptr_ptr)
{
*ptr_ptr = &global_var;
}
int main()
{
int var = 23;
int* pointer_to_var = &var;
cout << "Passing a pointer to a pointer to function " << endl;
cout << "Before :" << *pointer_to_var << endl; // display 23
changePointerValue(&pointer_to_var);
cout << "After :" << *pointer_to_var << endl; // display 42
return 0;
}
Output:
Passing a pointer to a pointer to function
Before :23
After :42
How to call a function with "Reference to pointer" parameter?
A reference allows called function to modify a local variable of the caller function. For example, consider the following example program where fun() is able to modify local variable x of main().
CPP
#include<iostream>
using namespace std;
void fun(int &x) {
x = 20;
}
int main() {
int x = 10;
fun(x);
cout<<"New value of x is "<<x;
return 0;
}
Output:
New value of x is 20
Below program shows how to pass a "Reference to a pointer" to a function:
CPP
#include <iostream>
using namespace std;
int gobal_var = 42;
// function to change Reference to pointer value
void changeReferenceValue(int*& pp)
{
pp = &gobal_var;
}
int main()
{
int var = 23;
int* ptr_to_var = &var;
cout << "Passing a Reference to a pointer to function" << endl;
cout << "Before :" << *ptr_to_var << endl; // display 23
changeReferenceValue(ptr_to_var);
cout << "After :" << *ptr_to_var << endl; // display 42
return 0;
}
Output:
Passing a Reference to a pointer to function
Before :23
After :42
Returning a pointer from a function
CPP
#include <iostream>
using namespace std;
int global_var = 42;
// function to return a pointer
int* returnPointerValue()
{
return &global_var;
}
int main()
{
int var = 23;
int* ptr_to_var = &var;
cout << "Return a pointer from a function " << endl;
cout << "Before :" << *ptr_to_var << endl; // display 23
ptr_to_var = returnPointerValue();
cout << "After :" << *ptr_to_var << endl; // display 42
return 0;
}
Output:
Return a pointer from a function
Before :23
After :42
Returning reference from function
CPP
#include <iostream>
using namespace std;
int global_var = 42;
// function to return reference value
int& ReturnReference()
{
return global_var;
}
int main()
{
int var = 23;
int* ptr_to_var = &var;
cout << "Returning a Reference " << endl;
cout << "Before :" << *ptr_to_var << endl; // display 23
ptr_to_var = &ReturnReference();
cout << "After :" << *ptr_to_var << endl; // display 42
return 0;
}
Output:
Returning a Reference
Before :23
After :42
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