Detailed explanation of C++ function parameters: differences between dark and shallow copies of reference parameters

In C, parameters passed to functions can be divided into value passing and reference passing. There are two types of reference parameters: shallow copy references and deep copy references. A shallow copy reference passes the reference itself to the function, allowing the function to modify the original object. A deep copy reference passes a copy of the object referenced by the reference parameter. Modifications to the copy by the function will not affect the original object. Use shallow copy references when functions need to modify objects, and also use shallow copy references when avoiding unnecessary copies. Deep copy references are used when the function should not modify the object or when the object is immutable.

C Detailed explanation of function parameters: The difference between dark and shallow copies of reference parameters

In C, there are two main types of parameters passed to functions: value transfer and Passed by reference. Reference parameters work by passing a reference to an object or variable, rather than a copy of it, in contrast to passing by value.

Reference parameter types

There are two reference parameter types:

• Shallow copy reference: The reference parameter itself is passed to the function, and Not the object it refers to. It allows functions to modify the original object.
• Deep copy reference: What is passed is a copy of the object referenced by the reference parameter. Modifications to the copy by the function will not affect the original object.

Code example

The following figure shows the difference between the two reference parameter types:

// 浅拷贝引用
void shallow_copy(int& a) {
  a++;
}

// 深拷贝引用
void deep_copy(const int& a) {
  int b = a;
  b++;
}

int main() {
  int x = 5;

  // 浅拷贝引用示例
  shallow_copy(x); // 改变 x 的值
  cout << "x after shallow copy: " << x << endl;  // 输出 6

  // 深拷贝引用示例
  deep_copy(x); // 不改变 x 的值
  cout << "x after deep copy: " << x << endl;  // 输出 5
  
  return 0;
}

Usage scenario

Shallow copy reference in Useful in the following situations:

• When the function needs to modify the object or variable passed in.
• When the object or variable passed in is large, avoid unnecessary copying.

Deep copy references are useful in the following situations:

• When the function should not modify the object or variable passed in.
• When the object or variable passed in is immutable.

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