Why Can\'t a Non-Const Lvalue Reference Bind to an Lvalue of a Different Type in C ?

Lvalue Reference Binding Errors

In C , references provide a mechanism to access data indirectly. However, certain restrictions apply when binding references to lvalues (objects stored at memory locations). Understanding these restrictions is crucial for correct and efficient code.

One such restriction arises when attempting to bind a non-const lvalue reference to an lvalue of a different type. For instance, the following code snippet is valid:

int a;
const double &m = a;

Here, a const double reference m can bind to an int lvalue a because the data type of m is wider than that of a. However, when we try to do the following:

int a;
double &m = a;

An error occurs: "non-const lvalue reference to type 'double' cannot bind to a value of unrelated type 'int'." This error stems from the fact that a non-const lvalue reference cannot bind to a temporary object.

In the second code snippet, the lvalue a is being converted to a double type. This conversion creates a temporary object. However, a non-const lvalue reference like m cannot bind to this temporary object.

This restriction applies equally to user-defined types:

struct Foo {};

Foo &obj = Foo(); // Error: non-const reference cannot bind to temporary object

In some compilers like Visual Studio, the error may not appear due to default compiler extensions. However, compliant compilers like GCC will raise this error. Therefore, it is essential to adhere to these rules to ensure code correctness and avoid potential issues.

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