Passing and Returning References

When passing or returning references in C++, there are a few important things to keep in mind:

1. Avoid returning references to local variables. Local variables are destroyed when the function returns, so returning a reference to a local variable will result in a reference to invalid memory.
2. Be careful when storing a returned reference. If the reference was to a temporary object, that object will be destroyed and the reference will become invalid.
3. Pass by const reference whenever possible to avoid unnecessary copying and to make it clear that the function will not modify the object.

Here's an example of a bad practice - returning a reference to a local variable:

1int& BadFunction() {
2  int x = 10;
3  // Error: returning reference to local variable
4  return x; 
5}

Instead, you could return by value:

1int GoodFunction() {
2  int x = 10;
3  return x; // Okay: returning by value
4}

Or, if you really need to return a reference, make sure it's to a non-local variable:

1int global_x = 10;
2
3int& OkayFunction() {
4  // Okay: returning reference to global variable
5  return global_x;
6}

But in general, returning by value is safer and often just as efficient due to compiler optimizations.