Constructors and Destructors

This post looks into some details about class constructors and destructors. First look at a piece of code in the following.


What's going on really with above code? Which objects were constructed and destructed? What's the order and logic relationship? Below is the output by above program. (The comments were added for explanation.)

default constructor: 1st           // initialize f1 with value "1st"
before calling func ...
copy constructor: 1st              // construct local object f in func
within function func ...
copy constructor: 1st              // initialize f2, no temporary object returned
destructor: 1st                    // destroy local object f
after calling func ...
default constructor: 3rd           // initialize f3 with value "3rd"
default constructor: default       // initialize f4 with default value
default constructor: 4th           // temporary object with value "4th"
f4.buf: 4th                        // after shallow copy to f4
destroying temporary object ...
destructor: 4th                    // destroy temporary object
f4.buf:                            // f4.buf becomes invalid
destroying local objects ...
destructor:                        // destroy f4
destructor: 3rd                    // destroy f3
destructor: 1st                    // destroy f2
destructor: 1st                    // destroy f1

If no copy constructor was defined, the function call may bring some problems because of shallow copy. When exiting the function func, the destroy of local variable f will also make the buf member of returned object invalid.