The essence and principle of function parameter passing

Function parameter passing essentially determines how the function obtains and modifies external variables. Under pass-by-value, the function obtains a copy of the value of the incoming variable, and modifications to the copy do not affect the external variables; under pass-by-reference, the function directly receives the reference to the external variable, and modifications to the parameters also modify the external variables.

The essence and principle of function parameter passing

Introduction
In programming, function parameters Passing is a crucial concept that determines how functions obtain and modify external variables. In this article, we will delve into the nature and principles of function parameter passing, and deepen our understanding through practical cases.

How to pass function parameters
In different programming languages, the way to pass function parameters may be different. The following are the two most common ways of passing:

• Pass by value: The function gets a copy of the value of the variable passed in. Modifications to the copy within a function do not affect external variables.
• Pass by reference: The function directly receives the reference of the external variable. Modifications to parameters within a function also modify external variables.

Practical example:
To understand function parameter passing, let us consider the following C code:

void increment(int n) {
  n++;
}

int main() {
  int x = 5;
  increment(x);
  cout << x;  // 输出：5
}

In this example, increment The function passes parameters by value. n inside the function is a copy of the external variable x. Modifications to n will not affect the value of x. Therefore, the x printed in the main function is still 5.

Now, let us modify the code and change the increment function to pass by reference:

void increment(int& n) {
  n++;
}

int main() {
  int x = 5;
  increment(x);
  cout << x;  // 输出：6
}

This time, the increment function uses pass by reference Pass parameters via pass. n inside the function directly points to the external variable x. Modifications to n directly modify the value of x. Therefore, the x printed in the main function is 6.

Summary

• The function parameter passing method determines how the function obtains and modifies external variables.
• In pass-by-value, the function obtains a copy of the value of the external variable.
• In pass-by-reference, the function directly receives the reference of the external variable.

The above is the detailed content of The essence and principle of function parameter passing. For more information, please follow other related articles on the PHP Chinese website!