What happens when passing reference to literal in C++?

What happens here:

double foo( const double& x ) {
   // do stuff with x
}

foo( 5.0 );

1. Does the compiler create an anonymous variable and sets its value to 5.0?
2. Does the x reference a memory location in read-only memory? This is a weird phrasing, I know...

edit: I forgot the const keyword...

From stackoverflow

• 1. What compiler probably does create const literal, but that's not a variable.

  2. A non-const reference cannot point to a literal.

     $ g++ test.cpp test.cpp: In function int main()': test.cpp:10: error: invalid initialization of non-const reference of type 'double&' from a temporary of type 'double' test.cpp:5: error: in passing argument 1 of double foo(double&)'

  test.cpp:

  #include <iostream>
  
  using namespace std;
  
  double foo(double & x) {
   x = 1;
  }
  
  int main () {
   foo(5.0);
  
   cout << "hello, world" << endl;
   return 0;
  }
  

  On the other hand, you could pass a literal to a const reference as follows. test2.cpp:

  #include <iostream>
  
  using namespace std;
  
  double foo(const double & x) {
   cout << x << endl;
  }
  
  int main () {
   foo(5.0);
  
   cout << "hello, world" << endl;
   return 0;
  }
  

• A temporary variable is created for this purpose and it's usually created on stack.

  You could try to const_cast, but it's pontless anyway, since you can no longer access a variable once the function returns.

  Gilad Naor : This seems very inefficient to me. Wouldn't it be better to just create a memory location in Read Only segment with the declared value and use it instead of creating a variable on the stack? All behind the scenes, of course...

  sharptooth : That's implementation dependent anyway. And double is not that large.

  aJ : Temporary variable creation holds good for Objects as well. Instead of double if it were a Class then a temporary object would have got created and its constructor also would have got called.

  Gilad Naor : The question is specific to primitives. Creating a variable on the stack seems like a bit of waste, not just the memory (in case of recursion, maybe?!?!), but run-time wise as well. I guess implementation dependent is all there is...

  sharptooth : Not necessarily such a waste. If you pass a value allocated in static storage the code that accesses it will have to read it and this can reduce cache locality.