Create an object array in const object, NULL and nullptr, and C ++

Create an object array in const object, NULL and nullptr, and C ++
Zookeeper

1. defined as a class after const

# Include
 
  
Class area {public: int x; int y; mutable int z; // class member area (): x (10), y (10) not restricted by const ), z (2) {} void printxy () const // The local variable {z = z + 1; std :: cout <x <"" <y <"" <z <"\ n";} void add (int a) {x + =; y-= a;} void go () const {} protected: private :}; void main () {// The const object cannot reference non-const member functions. // internal variables cannot be changed. mutable exception const area * const p = new area; p-> go (); // p-> add (); // p = new area; // the pointer can change const area area1; area1.printxy (); // area1.add (1); area1.go (); // area1.x = 10; // This statement indicates that after the class is defined as const, the mutable value z can be changed to area1.z + = 4; area1.printxy (); std :: cin. get ();}
 

Running result:

2. NULL and nullptr

# Include
 
  
Void go (int num) {std: cout <"gonum" <std: endl;} void go (void * p) {std :: cout <"gop" <std: endl ;}// the NULL type in C ++ is int, and 0 void main () {// C ++ is strongly typed, strict type check void * p = nullptr; // nullgo (p) of C ++; // The result is gop // process go (NULL) based on the type ); // go (int num) is called and the result is gonumgo (nullptr); // The result is gopstd: cin. get ();}
 

3. Related to the button and Line_edit operations in QT

QString str1 = ui-> lineEdit-> text (); QString str2 = ui-> lineEdit_2-> text (); QString str3 = str1 + str2; ui-> lineEdit_3-> setText (str3); QString str1 = ui-> lineEdit-> text (); // obtain the text QString str2 = ui-> lineEdit_2-> text (); int db1 = str1.toInt (); int db2 = str2.toInt (); // convert int db3 = db1 + db2; QString str3; str3.setNum (db3); // functions can be reloaded. Many types of ui-> lineEdit_4-> setText (str3 ); // set the text to convert QString to str3.toStdString (). c_str;

4. related to new delete, malloc, and free

# Include
 
  
# Include
  
   
Class myclassA {public: myclassA () {std: cout <"create \ n ";}~ MyclassA () {std: cout <"delete \ n" ;}protected: private :}; void main () {// new delete automatic call to construct the Destructor myclassA * p = new myclassA; delete p; // only memory is allocated and the memory is released, myclassA * p1 = (myclassA *) malloc (sizeof (myclassA); free (p1); std: cin. get ();}
  
 

Case 2

# Include
 
  
Class myclass {public: int x; int y; public: myclass (int a, int B): x (a), y (B) {std :: cout <"constructor" <std: endl;} myclass (){}~ Myclass () {std: cout <"Destroy" <std: endl; //} public: void printxy (); protected: private:}; void myclass:: printxy () {std: cout <x <"" <y <std: endl;} myclass class1 (10, 11 ); // The global variables take precedence over the main function myclass class2 (11, 12); void change1 (myclass ** pp) {* pp = & class2;} void change2 (myclass * & p) {p = & class1;} void main22 () {myclass * p = & class1; p-> printxy (); change1 (& p); p-> printxy (); change2 (p); p-> printxy (); std: cin. get ();} void main11 () {// myclass * p = new myclass; myclass * p (new myclass (10, 9 )); // The constructor initializes p-> printxy (); myclass class1 (20, 1); myclass ** pp = & p; // The second-level pointer stores the address of the first-level pointer (* pp)-> printxy (); // The first-level class pointer (** pp ). printxy (); // Class 0 pointer std: cin. get ();} void main122 () {// myclass * p = (myclass *) malloc (sizeof (myclass); // free (p ); myclass * p = new myclass; delete p; std: cin. get ();}
 

5. Create an object Array

# Include "dialog. h" # include
 
  
Class morewindow {public: Dialog * p [5]; morewindow () {for (int I = 0; I <5; I ++) {p [I] = new Dialog; p [I]-> show (); p [I]-> move (I * 100, I * 100 );}}~ Morewindow () {for (int I = 0; I <5; I ++) {delete p [I] ;}} Dialog * operator [] (int I) {return p [I] ;}}; int main (int argc, char * argv []) {QApplication a (argc, argv); morewindow more1; more1 [3]-> hide (); // reload the subscript return a.exe c ();}
 

6. Create an object Array

# Include "mainwindow. h" # include
  
   
# Include
   
    
Class morewindows {public: MainWindow * p [5]; // pointer array. Each element is a pointer morewindows () {for (int I = 0; I <5; I ++) {p [I] = new MainWindow; p [I]-> show (); p [I]-> move (I * 100, I * 100 );}}~ Morewindows () {for (int I = 0; I <5; I ++) {delete p [I] ;}}; class morewindowss {public: mainWindow * p [5] [4]; morewindowss () {for (int I = 0; I <5; I ++) {for (int j = 0; j <4; j ++) {p [I] [j] = new MainWindow; p [I] [j]-> show (); p [I] [j]-> move (I * 130, j * 130 );}}}~ Morewindowss () {for (int I = 0; I <5; I ++) {for (int j = 0; j <4; j ++) {delete p [I] [j] ;}}}; // int a [5] int * p = a; int * p = new int [5]; // int * a [5] int ** p = a int ** p = new (int *) [5]; // int * a [3] [5] // int * (* p) [5] class morewindowsss {public: MainWindow ** p; // second-level pointer morewindowsss () {// p = (MainWindow **) malloc (sizeof (MainWindow *) * 5);} void init (int num) {p = new MainWindow * [5]; // when it is new, no parentheses need to be added for (int I = 0; I <5; I ++) {p [I] = new MainWindow; p [I]-> show (); p [I]-> move (num * 100, I * 100) ;}} void move (int x, int y) {for (int I = 0; I <5; I ++) {p [I]-> move (x * 100, y * 100) ;}} morewindowsss & operator = (morewindowsss const & more) // write your own deep copy {qDebug () <"shen"; this-> p = new MainWindow * [5]; for (int I = 0; I <5; I ++) {p [I] = new MainWindow; p [I]-> show (); p [I]-> move (500, I * 100 );} return * this ;}~ Morewindowsss () {for (int I = 0; I <5; I ++) {delete p [I];} delete [] p; // free (p) ;}}; class morewindowssss {public: // MainWindow * p [5] [4]; // two-dimensional array, every element is a pointer MainWindow ** pA; // second-level pointer MainWindow * (* p) [4]; // pointer to a two-dimensional pointer array morewindowssss () {pA = new MainWindow * [20]; // One-dimensional array p = (MainWindow * (*) [4]) pA; for (int I = 0; I <5; I ++) {for (int j = 0; j <4; j ++) {p [I] [j] = new MainWindow; p [I] [j]-> show (); p [I] [j]-> move (I * 130, j * 130) ;}}}~ Morewindowssss () {for (int I = 0; I <5; I ++) {for (int j = 0; j <4; j ++) {delete p [I] [j] ;}} delete [] pA ;}}; int main (int argc, char * argv []) {QApplication a (argc, argv); morewindowsss more1; more1.init (1); // more1.move (1, 2); morewindowsss more2; // copy to construct more2 = more1; // assign a value // morewindowsss more2 (more1 ); more2.move (3, 4); return a.exe c ();}