The relationship between the C++ function parameter passing method and the collection class library

C The function parameter passing method affects the implementation of the collection class library. There are three passing methods: passing value (copy), passing reference (direct access to the original variable) and passing pointer (indirect access to the original variable). Collection class libraries usually use passing references or pointers to optimize performance and safety. For example, STL containers use passing references to avoid copy overhead. In specific applications, the delivery method should be selected based on whether the function needs to modify the container, and the trade-off between performance and memory overhead should be considered.

C The relationship between the function parameter passing method and the collection class library

In C, the function parameter passing method affects the collection Class library implementation. Different delivery methods have effects on performance, security, and other aspects.

Transfer method

There are three function parameter transfer methods in C:

• Pass-by-value : Create a copy of the original variable and pass the copy to the function. Changes in the function do not affect the original variable.
• Pass-by-reference: Does not create a copy, but passes the address of the original variable. Changes in the function are reflected in the original variable.
• Pass-by-pointer: Similar to passing a reference, but passing a variable pointer instead of an address. Changes in the function are reflected in the original variable.

Applications in collection libraries

Collection libraries usually use different delivery methods to optimize performance and security:

• Standard Template Library (STL): Containers such as

  • vector and deque are usually passed by reference. Pass an iterator to avoid copy overhead. Associative containers such as
  • map and set access keys and values ​​by passing references to maintain the association between elements.

• boost library:

  • boost::optional and boost:: Smart pointer types such as variant use pass-by-reference to access the underlying value.

Practical case

Suppose we have a function that processes a collection of integersprocess_ints：

void process_ints(vector<int>& numbers) {
  for (int& num : numbers) {
    num += 1;
  }
}

• Pass value: Pass in a copy of the numbers container of process_ints. Changes in the function do not affect the original container.

vector<int> numbers = {1, 2, 3};
process_ints(numbers); // 原始容器仍为 {1, 2, 3}

• Pass reference: Pass directly into the original numbers container. Changes in the function are reflected on the original container.

vector<int>& numbers = {1, 2, 3};
process_ints(numbers); // 原始容器变为 {2, 3, 4}

• Passing a pointer: Passing in a pointer to the original numbers container is essentially the same as passing a reference.

vector<int>* numbers = new vector<int>{1, 2, 3};
process_ints(*numbers); // 原始容器变为 {2, 3, 4}

Choose the appropriate passing method

Choosing the appropriate parameter passing method depends on the specific situation:

• If the function requires When modifying the container, pass a reference or pointer to avoid unnecessary copies.
• If the function should not modify the container, pass a value or use a constant reference.
• Consider the performance and memory overhead trade-offs, especially for large containers.

By understanding the relationship between function parameter passing methods and collection class libraries, you can optimize code performance and enhance security.

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