C++ Primer Plus

Don’ts and Dos

The following excerpt contains two examples of what not to do and one example of a good constructor:

String::String(){   str = "default string";     // oops, no new []   len = std::strlen(str);}String::String(const char * s){   len = std::strlen(s);   str = new char;             // oops, no []   std::strcpy(str, s);        // oops, no room}String::String(const String & st){       len = st.len;       str = new char[len + 1];      // good, allocate space       std::strcpy(str, st.str);     // good, copy value}

The first constructor fails to use new to initialize str. The destructor, when called for a default object, applies delete to str. The result of applying delete to a pointer not initialized by new is undefined, but it is probably ...