Lvalue and Lvalue Reference

Phần 1

Lvalue

An lvalue identifies an existing object.

int price = 100;
price = 101;

price is an lvalue because it identifies an existing object.

Phần 2

Lvalue Reference

An lvalue reference is another name for an existing object.

int& ref = price;
ref = 102;

Changing ref changes price because both names refer to the same object.

Phần 3

Function Parameter

void update(double& value);

A non-const lvalue-reference parameter allows a function to modify the original object supplied by the caller.

Phần 4

Const Reference

void inspect(const double& value);

Use a const lvalue reference to read an object without copying it and without allowing the function to modify it through that reference.

Phần 5

Key Rules

Passing a parameter by value creates a separate parameter object.
A non-const T& refers to the original object and can modify it.
A const T& reads the original object without copying or modifying it through that reference.

Mã mẫu hoàn chỉnh

cpp11/19_21_lvalue/main.cpp

C++

#include <iostream>

void update(double& price)
{
    price += 0.5;
}

int main()
{
    double bid = 100.0;
    double& ref = bid;

    update(ref);

    std::cout << bid << '\n';
}

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