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What is double address operator(&&) in C++?
&& is a new reference operator defined in the C++11 standard. int&& a means "a" is an r-value reference. && is normally only used to declare a parameter of a function. And it only takes an r-value expression.
Simply put, an r-value is a value that doesn't have a memory address. E.g. the number 6, and character 'v' are both r-values. int a, a is an l-value, however (a+2) is an r-value.
example
void foo(int&& a)
{
//Some magical code...
}
int main()
{
int b;
foo(b); //Error. An rValue reference cannot be pointed to a lValue.
foo(5); //Compiles with no error.
foo(b+3); //Compiles with no error.
int&& c = b; //Error. An rValue reference cannot be pointed to a lValue.
int&& d = 5; //Compiles with no error.
}You can read more about R-values and this operator at http://blogs.msdn.com/b/vcblog/archive/2009/02/03/rvalue-references-c-0x-features-in-vc10-part-2.aspx
Updated on: 11-Feb-2020
15K+ Views
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