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1.定义成了const之后的类
#include
class area
{
public:
int x;
int y;
mutable int z; //不受const约束的类成员
area() :x(10), y(10), z(2)
{
}
void printxy()const //不可以访问类中局部变量
{
z = z + 1;
std::cout << x << " " << y << " " << z << "\n";
}
void add(int a)
{
x += a;
y -= a;
}
void go()const
{
}
protected:
private:
};
void main()
{
//const对象不可以引用非const成员函数
//不可以改变内部变量,mutable例外
const area * const p = new area;
p->go();
//p->add();
//p = new area;//指针可以改变
const area area1;
area1.printxy();
//area1.add(1);
area1.go();
//area1.x = 10;
//这一句说明当把类定义成const之后，定义成了mutable的值z可以修改
area1.z += 4;
area1.printxy();
std::cin.get();
}
运行结果：
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2.NULL和nullptr
#include
void go(int num)
{
std::cout << "gonum" << std::endl;
}
void go(void *p)
{
std::cout << "gop" << std::endl;
}
//C++中的NULL的类型是int ,0
void main()
{
//C++是强类型，严格的类型检查
void *p = nullptr;//C++的null
go(p); //结果为gop //根据类型来处理
go(NULL); //会调用go(int num) 结果为gonum
go(nullptr); //结果为gop
std::cin.get();
}
3.QT中button和Line_edit操作相关的
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();//获取文本
QString str2=ui->lineEdit_2->text();
int db1=str1.toInt();
int db2=str2.toInt();//转换
int db3=db1+db2;
QString str3;
str3.setNum(db3);//函数可以重载，很多个类型
ui->lineEdit_4->setText(str3);//设置文本
将QString转换成为字符串的是：str3.toStdString().c_str;
4.new delete和malloc，free相关
#include
#include
class myclassA { public: myclassA() { std::cout << "create\n"; } ~myclassA() { std::cout << "delete\n"; } protected: private: }; void main() { //new delete自动调用构造析构 myclassA *p = new myclassA; delete p; //只会分配内存，释放内存，不会对内存进行操作 myclassA *p1 = (myclassA *)malloc(sizeof(myclassA)); free(p1); std::cin.get(); }
案例2
#include
class myclass
{
public:
int x;
int y;
public:
myclass(int a, int b) :x(a), y(b)
{
std::cout << "构造哦" << std::endl;
}
myclass()
{
}
~myclass()
{
std::cout << "销毁哦" << std::endl;//
}
public:
void printxy();
protected:
private:
};
void myclass::printxy()
{
std::cout << x << " " << y << std::endl;
}
myclass class1(10, 11);//全局变量优先main函数
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));//构造函数初始化
p->printxy();
myclass class1(20, 1);
myclass ** pp = &p;//二级指针存储一级指针的地址
(*pp)->printxy();//一级类指针
(**pp).printxy();//0级类指针
std::cin.get();
}
void main122()
{
//myclass *p = (myclass *)malloc(sizeof(myclass));
//free(p);
myclass *p = new myclass;
delete p;
std::cin.get();
}
5.创建对象数组
#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();//重载下标
return a.exec();
}
6.创建对象数组
#include "mainwindow.h"
#include
#include
class more
windows { public: MainWindow *p[5];//指针数组，每一个元素是指针 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;//二级指针 morewindowsss() { // p= (MainWindow **)malloc(sizeof(MainWindow *)*5); } void init(int num) { p= new MainWindow * [5];//new的时候类型不需要加上括号 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)//自己写的深拷贝 { 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];//二维数组，每一个元素都是指针 MainWindow **pA;//二级指针 MainWindow *(*p)[4];//指向二维指针数组的指针 morewindowssss() { pA=new MainWindow *[20];//一维数组 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;//拷贝构造 more2=more1;//赋值 // morewindowsss more2(more1); more2.move(3,4); return a.exec(); }