What are the ways to pass function parameters in C++?

In C, parameters passed to a function can be passed in three ways: pass by value (create a copy of the formal parameter), pass by reference (directly access the actual parameter), and pass by pointer (access the memory address of the actual parameter). Choose the best delivery method based on function behavior and memory management requirements, weighing the trade-offs between copy creation, direct modification, and memory management.

How to pass function parameters in C

In C, the parameters passed to the function can be passed in a variety of ways , which have different effects on function behavior and memory management.

Pass by value

The most basic and most commonly used parameter passing method is pass by value. In this way, the values ​​of the actual parameters are copied to the formal parameters of the function. This creates an independent copy of the formal parameters, so any changes made to the formal parameters do not affect the actual parameters.

Code example:

int func(int value) {
  // 对形参 value 的操作
  // ...
}

int main() {
  int x = 10;
  func(x); // 传值传递
  // x 仍然为 10，不受函数内的更改影响
}

Pass by reference

Pass by reference refers to passing the reference of the actual parameter to the formal parameter of the function. This allows the function to directly access and modify the actual parameter itself, rather than just a copy of it.

Code example:

void func(int& ref) {
  // 对实参的引用 ref 的操作
  // ...
}

int main() {
  int x = 10;
  func(x); // 传引用传递
  // x 被修改，现在为函数中所做的更改后的值
}

Passing by pointer

Passing a pointer means passing a pointer to an actual parameter to a formal parameter of a function. This is similar to passing by reference, but it allows more granular memory management.

Code example:

void func(int* ptr) {
  // 对指向实参的指针 ptr 的操作
  // ...
}

int main() {
  int x = 10;
  func(&x); // 传指针传递
  // x 被修改，现在为函数中所做的更改后的值
}

Practical case

In actual applications, choosing the most appropriate transfer method depends on the behavior of the function and the memory management requirements .

The main advantage of pass by reference and pass by pointer is that they allow the function to directly access and modify the actual parameters, while pass by value creates a copy of the formal parameter and has no effect on the actual parameter.

On the other hand, passing by reference and passing by pointer also have some disadvantages. For example, if the argument is a local variable, the local variable must persist during the function scope when passed by reference or pointer. Additionally, pointer operations are more complex than reference operations and can be error-prone.

Therefore, when choosing a parameter passing method, these factors must be weighed to find the most appropriate solution for your specific needs.

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