c ++ initialization

1. Built type default initialization

　　If there is no built-in types are displayed initialized, it will be the compiler default initialization. According to the type of the variable initialization ① ② different types of position variables to determine the value after initialization. But if the built-in types inside the function body, it will not be initialized - that is undefined, while operating an undefined variable can cause errors. As will therewith, string type will provide a default initialization, so the line 21 by operation on the variable str.

. 1 #include <the iostream>
 2 #include < String >
 . 3  the using  namespace STD;
 . 4  
. 5  int I; // definition function in vitro, it will be initialized to 0
 . 6  static  int K;
 . 7  
. 8  int main ()
 . 9  {
 10      COUT I << << endl;
 . 11      COUT << K << endl;
 12 is      
13 is      int j;
 14      // I = j; // illegal, j defined as
 15      // COUT << j << endl; //   same illegal 
16 
. 17      static  int G;
 18 is      COUT G << << endl; // valid 
. 19   
20 is      String STR, ST ( " 23 is " );
 21 is      ST = STR; // legal, string class provides a suitable default value 
22 }