How to use reference parameters in C++ functions

Reference parameters point directly to the variables passed to the function, providing efficiency, modifiability and security. Specifically, reference parameters improve efficiency (avoiding copies), allow functions to modify variables in the caller, and eliminate the risk of dangling references. The syntax is to add & before the type name, such as void foo(int& x);. In practice, using reference parameters to pass the radius can save the cost of copying the radius value. Precautions include initializing reference parameters, not modifying the address, and still pointing to the original variable after the call.

How to use reference parameters in C functions

In C, Reference parameters are parameters of the function, which point directly to the call Variables passed to the function. This is different from value parameters, which copies and stores the passed value. Using reference parameters provides several benefits:

• Efficiency: The overhead of copying the original value is avoided, thereby improving efficiency.
• Modifiability: When passing a reference, the function can modify the value of the actual variable in the calling function.
• Safety: Avoids the risk of dangling references pointing to destroyed variables.

Syntax

To declare a reference parameter, add the symbol & before the type name:

void foo(int& x);

Practical case

Let us consider a function that calculates pi π. Passing the radius by reference parameter can save the overhead of copying the radius value:

#include <iostream>
#include <cmath>

using namespace std;

void calculatePi(double& pi, double radius) {
  pi = 2 * acos(-1.0) * radius;
}

int main() {
  double pi;
  double radius = 2.5;

  calculatePi(pi, radius);

  cout << "Pi: " << pi << endl;

  return 0;
}

In the calculatePi function, pi is a reference parameter, allowing the function to directly modify pi variable. So, in the main function, when radius changes, pi is updated accordingly.

Notes

When using reference parameters, you need to pay attention to the following:

• Reference parameters must be initialized and point to a valid variable.
• Functions must not modify the address of a variable passed as a reference parameter.
• After the function is called, the reference still points to the original variable, so any changes to it will be reflected in the original variable.

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