Question

Possible Duplicate:
return type in c++

#include<iostream>
int& fun();
int main()
{
  int p=fun();
  std::cout<<p;
  return 0;
}

int & fun()
{
  int a=10;
  return  &a;
}

why does this code give error as,error: invalid initialization of non-const reference of type 'int&' from a temporary of type 'int*'..Actually i am not clear about the temporaries i.e. when are they created and when are they get destroyed.?so ,please explain temporaries to some extent too.

Answer 1

&a generates a temporary which cannot be bound to a non-const reference.

Moreover your code has several flaws.

1) &a has type int* whereas you are returning by reference i.e int &. The types don’t match.

2) Even if you change &a to a in the return statement you code still won’t work because returning a local variable by reference and then using the result is UB.

---

Invalid initialization of non-const reference from a temporary

C++ doesn’t allow temporaries to be bound to non constant references.

For example you can’t do something like this

int &x = 5; 

because the temporary int(5) would be destroyed at the end the expression which it is a part of. However references to const can be initialized from a temporary i.e you can safely write

const int &x = 5;

In this case attaching the temporary to a const-reference prolongs its lifetime. It gets destroyed when x gets destroyed.