How to pass function parameters in C++

C There are three ways to pass function parameters: passing a copy by value, passing a reference by reference, and passing a pointer by pointer. Passing by value does not affect the actual parameters, passing by reference and pointer do.

C How to pass function parameters

In C, function parameters can be passed by reference, pointer or value. Here are introductions and practical examples of each passing method:

Pass-by-value

Pass a copy of the function argument. Any modifications to the copy will not affect the actual parameters passed.

void swap(int x, int y) {
  int temp = x;
  x = y;
  y = temp;
}

int main() {
  int a = 10, b = 20;
  std::cout << "Before swap: a = " << a << ", b = " << b << std::endl;
  swap(a, b);  // a 和 b 的副本被传给 swap
  std::cout << "After swap: a = " << a << ", b = " << b << std::endl;
  return 0;
}

Output:

Before swap: a = 10, b = 20
After swap: a = 10, b = 20

Pass-by-reference

Pass a reference to a function parameter. Any modification to the reference will affect the actual parameters passed.

void swap(int &x, int &y) {
  int temp = x;
  x = y;
  y = temp;
}

int main() {
  int a = 10, b = 20;
  std::cout << "Before swap: a = " << a << ", b = " << b << std::endl;
  swap(a, b);  // a 和 b 的引用被传给 swap
  std::cout << "After swap: a = " << a << ", b = " << b << std::endl;
  return 0;
}

Output:

Before swap: a = 10, b = 20
After swap: a = 20, b = 10

Pass-by-pointer

Pass the pointer of the function parameter. Any modification to the memory pointed to by the pointer will affect the actual parameters passed.

void swap(int *x, int *y) {
  int temp = *x;
  *x = *y;
  *y = temp;
}

int main() {
  int a = 10, b = 20;
  std::cout << "Before swap: a = " << a << ", b = " << b << std::endl;
  swap(&a, &b);  // a 和 b 的指针被传给 swap
  std::cout << "After swap: a = " << a << ", b = " << b << std::endl;
  return 0;
}

Output:

Before swap: a = 10, b = 20
After swap: a = 20, b = 10

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