8.4. Pass-by-Reference with Pointers

There are three ways in C++ to pass arguments to a function—pass-by-value, pass-by-reference with reference arguments and pass-by-reference with pointer arguments. Chapter 6 compared and contrasted pass-by-reference with reference arguments and pass-by-value. Here, we explain pass-by-reference with pointer arguments.

Chapter 6 showed that return can return one value from a called function or simply return control. You also learned that arguments can be passed to a function using reference parameters, which enable the called function to modify the original values of the arguments in the caller. Reference parameters also enable programs to pass large data objects to a function and avoid the overhead of passing the objects by value (which, of course, copies the object). Pointers, like references, also can be used to modify one or more variables in the caller or to pass pointers to large data objects to avoid the overhead of passing the objects by value.

You can use pointers and the indirection operator (*) to accomplish pass-by-reference (exactly as pass-by-reference is done in C programs—C does not have references). When calling a function with an argument that should be modified, the address of the argument is passed. This is normally accomplished by applying the address operator (&) to the name of the variable whose value will be modified.