C ++ pointer-pointer advanced-

 

// ----------------------------------------------- char   * GetMemory2( void ){   char  p[]  =   " hello world " ;return  p;} void  Test2( void ){char   * str  =  NULL;str  =  GetMemory2();  printf(str);} // ----------------------------------------------- void  GetMemory3( char   ** p,  int  num){* p  =  ( char   * )malloc(num);} void  Test3( void ){char   * str  =  NULL;GetMemory3( & str,  100 );strcpy(str,  " hello " );  printf(str);    } // ----------------------------------------------- void  Test4( void ){char   * str  =  ( char   * ) malloc( 100 );strcpy(str,  " hello " );free(str);      if (str  !=  NULL){strcpy(str,  " world " ); printf(str);} } 

　　

// -----------------------------------------------/* What is the result of running the test1 function? A: The program crashes. Because getmemory cannot pass dynamic memory, STR in the test function is always null. Strcpy (STR, "Hello World"); will crash the program. */Test1 (); // ------------------------------------------------- // what kind of results will the function run? //// A: It may be garbled. //// Because getmemory returns a pointer pointing to the "stack memory", // the address of this pointer is not null, but its original content has been cleared, and the new content is unknown. Test2 (); // ------------------------------------------------- // what kind of results will the function run? //// A: //// (1) Hello // (2) Memory leakage test3 (); // ----------------------------------------------- // What is the result of running the test function? /// Answer: tampering with the content in the dynamic memory area is unpredictable and dangerous. //// Because free (STR); then, STR becomes a wild pointer, /// if (STR! = NULL) the statement does not work. Test4 ();//-----------------------------------------------

Source Address: http://www.cppblog.com/mzty/archive/2006/07/07/9536.html