CODEWITHSUNDEEP
c++
Jeff
Jeff

Reputation: 463

What does it mean when someone says an reference cannot be changed in C++

Recently, I am reading some books about C++ such as "C++ primer" and "Effective C++".Almost every books say that a reference cannot be changed. I am confused with this statement. Because, I can write down code like this.

int a = 1, b = 2;
int& c = a;
// then I can change the reference c without compile errors.
c = b;

So, I cannot understand what dost it mean a reference cannot be changed.

Upvotes: 1

Views: 1203

Answers (4)

Kaustav Ray
Kaustav Ray

Reputation: 754

c = b;

In the above statement you are assigning the value of b to the value of a as c is still referring to the the variable a

Upvotes: 0

yuan
yuan

Reputation: 2534

Pointers and reference are two mechanisms for referring to an object frome different places in a program without copying.

The consistence of reference can be understood by comparing with pointers. 

char a{'a'};
char b{'b'};
char *p = &a;
p = &b;

enter image description here The pointer p is pointer to different object changing from a to b. In the case of reference: 

char &r = a;
r = b;

enter image description here The reference in expression is always dereferenced automatically. So it with change the value of the object it referenced.

Upvotes: 2

Jonathan Potter
Jonathan Potter

Reputation: 37192

Once a reference is assigned to a target any further use of that reference refers to the target, not the reference itself.

For example, int& c = a; creates a reference called c whose target is a. But if you then try to change it, as in c = b; you are changing the value of a, not changing the target of c.

Upvotes: 2

godel9
godel9

Reputation: 7390

When people say that a reference cannot be changed, they mean that you cannot change which object the reference is referencing... For example, with pointers, you can do this:

int a = 1, b = 2;
int *c = &a; // c points to a
c = &b;      // c now points to b instead
*c = 3;      // b now equals 3

There's no equivalent code for references. Once you initialize the reference:

int a = 1, b = 2;
int &c = a;

You can't change the reference so that the statement c = 3; now changes b instead of a.

Upvotes: 6

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