C++ Primer Plus, Fourth Edition

Chapter 12

1:

Suppose a String class has the following private members: class String { private: char * str; // points to string allocated by new int len; // holds length of string //... } ; What's wrong with this default constructor? String::String() { } What's wrong with this constructor? String::String(const char * s) { str = s; len = strlen(s); } What's wrong with this constructor? String::String(const char * s) { strcpy(str, s); len = strlen(s); }

A1:

The syntax is fine, but this constructor leaves the str pointer uninitialized. The constructor should either set the pointer to NULL or use new [] to initialize the pointer. This constructor does not create a new string; it merely copies the address of the old string. It should use new [] and ...