The difference between left-side value reference and right-side value reference parameter of C++ function

The difference between the left-hand and right-hand value reference parameters in C is as follows: The left-hand value reference (&) points to an existing object and is used to modify its state. The right-hand value reference (&&) points to a temporary object used to get or pass its data.

The difference between the value reference on the left side and the value reference parameter on the right side of C function

Background## A reference in #C is an alias for a variable, allowing direct access to the memory of the underlying object. Understanding the difference between left-hand value references and right-hand value references is critical to using C references effectively.

Left side value referenceLeft side value reference (&) is used as a type that points to a reference to an existing object. They are used to modify the state of the original object.

Syntax:

int& lvalue_ref = variable;

Right side value referenceRight side value reference (&&) is used to point to a temporary object (only exists in the type of reference) in the expression. They are used to get data from temporary objects or pass them to other functions.

Grammar:

int&& rvalue_ref = std::move(temporary_object);

Practical case

Example 1: Exchange two numbers

void swap(int& a, int& b) {
  int temp = a;
  a = b;
  b = temp;
}

In this example, the

swap() function accepts two left-hand value references as parameters. This allows direct modification of the original values ​​of a and b.

Example 2: Passing a temporary object to a function

void print_value(int&& rvalue) {
  std::cout << "Value: " << rvalue << std::endl;
}

int main() {
  print_value(42);  // Temporary object created and passed as rvalue reference
  return 0;
}

In this example, the

print_value() function accepts a right-hand side value reference as parameter. This allows the incoming value to be read directly from the temporary object (42).

Note:

The left value reference modifies the original object, while the right value reference obtains the value of the temporary object.
• The value reference on the right cannot be bound to an existing object, but the value reference on the left can.
• Abuse of right-side value references can lead to persistence errors because temporary objects are destroyed after use.

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