在C ++中通过引用返回示例

C++中的指针和引用彼此之间保持着密切的关系。主要区别在于，可以像添加值一样操作指针，而引用只是另一个变量的别名。

• C++中的函数可以返回引用，因为它返回了指针。
• 当函数返回引用时，表示返回隐式指针。

通过引用返回与通过引用返回非常不同。当变量或指针作为引用返回时，函数起着非常重要的作用。

请参阅下面的“按引用返回”的函数签名：

dataType& functionName(parameters);
where,
dataType is the return type of the function,
and parameters are the passed arguments to it.

下面是说明按引用返回的代码：

CPP

// C++ program to illustrate return by reference
#include 
using namespace std;
  
// Function to return as return by reference
int& returnValue(int& x)
{
  
    // Print the address
    cout << "x = " << x
         << " The address of x is "
         << &x << endl;
  
    // Return reference
    return x;
}
  
// Driver Code
int main()
{
    int a = 20;
    int& b = returnValue(a);
  
    // Print a and its address
    cout << "a = " << a
         << " The address of a is "
         << &a << endl;
  
    // Print b and its address
    cout << "b = " << b
         << " The address of b is "
         << &b << endl;
  
    // We can also change the value of
    // 'a' by using the address returned
    // by returnValue function
  
    // Since the function returns an alias
    // of x, which is itself an alias of a,
    // we can update the value of a
    returnValue(a) = 13;
  
    // The above expression assigns the
    // value to the returned alias as 3.
    cout << "a = " << a
         << " The address of a is "
         << &a << endl;
    return 0;
}

输出：

x = 20 The address of x is 0x7fff3025711c
a = 20 The address of a is 0x7fff3025711c
b = 20 The address of b is 0x7fff3025711c
x = 20 The address of x is 0x7fff3025711c
a = 13 The address of a is 0x7fff3025711c

解释：

由于引用不过是另一个变量的别名(同义词)而已，因此a ， b和x的地址永远不会改变。

Note: We should never return a local variable as a reference, reason being, as soon as the functions returns, local variable will be erased, however, we still will be left with a reference which might be a security bug in the code.

下面是说明按引用返回的代码：

C++

// C++ program to illustrate return
// by reference
#include 
using namespace std;
  
// Global variable
int x;
  
// Function returns as a return
// by reference
int& retByRef()
{
    return x;
}
  
// Driver Code
int main()
{
    // Function Call for return
    // by reference
    retByRef() = 10;
  
    // Print X
    cout << x;
    return 0;
}

输出：

10

解释：
上面函数retByRef()的返回类型是变量x的引用，因此将值10分配给x。

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