561: Highlights

• C++ programs ordinarily use call-by-value parameters. Thus, the value of any parameter or variable that appears as an argument is copied into a memory chunk freshly reserved for the corresponding parameter. The effect of a parameter reassignment cannot propagate outside of the function in which the reassignment occurs.
• You can force the C++ compiler to treat a parameter as a call-by-reference parameter. Then, the memory chunk holding the value of any variable, parameter, array element, or dereferenced array pointer that appears as an argument is shared by the corresponding call-by-reference parameter. Therefore, the effect of a parameter reassignment can propagate outside of the function in which the reassignment occurs.
• One reason to force the C++ compiler to treat a parameter as a call-by-reference parameter is to ensure that the parameter provides access to all of a run-time–allocated object provided via a dereferenced pointer, rather than to only the superclass portion of that object.
• Another reason to force the C++ compiler to treat a parameter as a call-by-reference parameter is to save the time involved in copying an argument.
• Still another reason to force the C++ compiler to treat a parameter as a call-by-reference is to enable a function to modify an argument.
• If you want a parameter to be a call-by-reference parameter, rather than an ordinary call-by-value parameter, then add an ampersand to the parameter-type declaration in the parameter list:

  data type function name (..., 
                            data type& parameter name, 
                            ...)