What to do when a C++ function returns a structure or class?

In C, a function can return a structure or class by reference or copy: Return reference: Using the & symbol, the caller can modify the returned object, and the changes are reflected in the original object. Return a copy: By returning by value, the caller's modification of the copy will not affect the original object.

How to return a structure or class in C

In C, a function can return a structure or class, but this Unlike returning simple data types. In order to return a structure or class correctly, we need to understand the following concepts:

1. Reference

A reference is an alias for a variable. Like a pointer, a reference points to a specific memory address, but unlike a pointer, a reference cannot be reallocated to another address.

2. Return a reference to a structure or class

To return a reference to a structure or class, we use the & symbol. The following is an example:

struct Person {
    std::string name;
    int age;
};

Person& getPerson() {
    // ... 代码 ...
    Person person = { "John Doe", 30 };
    return person;
}

In this example, the getPerson() function returns a reference of type Person. The caller can modify the returned Person object, and the changes will be reflected in the original object.

3. Return a copy of the structure or class

If we do not want the caller to modify the original object, we can return a copy of the structure or class. To do this, we use the value return:

Person getPersonCopy() {
    // ... 代码 ...
    Person person = { "John Doe", 30 };
    return person;
}

In this example, the getPersonCopy() function returns a copy of type Person. The caller can modify the copy, but the changes are not reflected in the original object.

Practical case

Suppose we have a Employee class containing employee data:

class Employee {
public:
    std::string name;
    int salary;
};

We can write a function to Returns a reference or copy of the Employee class:

Employee& getEmployeeReference(int id) {
    // ... 代码 ...
    Employee employee;
    // 查找并返回具有给定 ID 的员工的引用
    return employee;
}

Employee getEmployeeCopy(int id) {
    // ... 代码 ...
    Employee employee;
    // 查找并返回具有给定 ID 的员工的副本
    return employee;
}

We can use these functions to get a reference or copy of the employee data as needed.

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