How to choose how to pass C++ function parameters?

When choosing a function parameter passing method in C, there are four options: passing by value, passing by reference, passing by pointer, and passing by const reference. Passing by value creates a copy of the parameter value and does not affect the original parameter; passing the reference of the parameter value by reference can modify the original parameter; passing the pointer of the parameter value by pointer allows the original parameter value to be modified through the pointer; passing the parameter value by const reference The const reference can only access the parameter value and cannot modify it.

How to choose the method of passing function parameters in C

In C, you can choose four ways to pass function parameters: Press Pass by value, pass by reference, pass by pointer and pass by const reference. Correctly choosing the delivery method can improve the efficiency and security of your code.

Pass by value

• A copy of the parameter value is passed to the function.
• Any modification to the parameter value will not affect the original parameters in the calling function.
• Suitable for small and immutable parameters.
• Example:

void swap(int a, int b) {
  int temp = a;
  a = b;
  b = temp;
}
int main() {
  int x = 1, y = 2;
  swap(x, y); // x 和 y 保持不变
  return 0;
}

Pass by reference

• The parameter value is passed by reference to the function.
• Any modification of the parameter value by the function will affect the original parameters in the calling function.
• Suitable for large or complex parameters that require modification of the original parameters.
• Example:

void swap(int& a, int& b) {
  int temp = a;
  a = b;
  b = temp;
}
int main() {
  int x = 1, y = 2;
  swap(x, y); // x 和 y 值被交换
  return 0;
}

Passing by pointer

• The pointer of the parameter value is passed to the function.
• The function can modify the original parameter value through the pointer.
• Applicable to situations where indirect operations on data need to be performed inside and outside functions.
• Example:

void swap(int* a, int* b) {
  int temp = *a;
  *a = *b;
  *b = temp;
}
int main() {
  int x = 1, y = 2;
  swap(&x, &y); // x 和 y 值被交换
  return 0;
}

Passing by const reference

• The const reference of the parameter value is passed to the function.
• The function can access the passed parameter value, but cannot modify it.
• Applicable to situations where it is necessary to ensure that the parameter value will not be modified by the function.
• Example:

void print(const int& a) {
  std::cout << a << std::endl;
}
int main() {
  int x = 1;
  print(x); // x 的值被打印，但不会被修改
  return 0;
}

Practical case

The following list shows practical examples of selecting different delivery methods:

• Pass by value: Pass small or immutable parameters, such as numbers or strings.
• Pass by reference: Passing large or complex parameters, such as arrays or complex structures, requires modification of the original parameters.
• Pass by pointer: indirect operations on data are required, such as traversing in a data structure.
• Pass by const reference: You need to ensure that the parameter value will not be modified in the function, such as printing debugging information.

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