朝花夕拾－－C++再学习

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/M_sdn/article/details/86535610

一，寻址

1. 通过变量名
2. 通过内存地址

取地址运算符&，用来获得变量的地址．

[code]void getAddress() {
int var;
cout<<"var address is: "<<&var<<endl;
}

输出结果是：var address is: 0x7ffcf4dd4e14

为何这里是12位的16进制呢，换成2进制就是48位，难道我的机器不是64位机吗？ 

二，对齐

内存对齐，文件对齐

程序在编译链接后会被分割成一个个区块，而区块在内存和文件中按照一定的规律对齐．

//32位系统内存对齐值是：1000H == 4KB
//64位系统内存对齐值是：2000H == 8KB
//文件对齐值是：200H  

操作系统处理内存时内存页是4KB

https://www.geek-share.com/detail/2644386865.html 

三，指针

既然指针变量存放的是一个地址，而32位系统的地址都是4个字节，为什么不用一个整型变量来存储而要发明指针呢？

如何根据指针变量来获取指针所存地址对应的值？－－Deference(解引用)，即在指针变量前加*号．

如std::cout<<*aPtr<<endl;

因此1，变量a和a的指针aPtr，代表同一个值，即a == *aPtr;

因此2，*aPtr = -100，将会修改a的值．

(1) *的两种用途：

1. 用于创建指针

[code]int *mPtr = &myInt;

2. 对指针进行解引用

[code]*mPtr = 123456;

(2) 指针与数组

数组的名字就是一个指针，它指向数组的基地址(也就是第一个元素的地址)．因此，下面两句等价：

[code]int *arrPtr1 = &mArray[0];
int *arrPtr2 = mArray;

指针式遍历数组：intPtr++;

[code]void travesalArray(){
const unsigned short SIZE = 5;

int intArr[SIZE] = {1,2,3,4,5};
char charArr[SIZE] = {'F','i','s','C','o'};

int *intPtr = intArr;
char *charPtr = charArr;

cout<<"intager array output: "<<endl;
for(int i=0; i<SIZE; i++){
cout<<*intPtr<<" at "<<reinterpret_cast<unsigned long>(intPtr)<<endl;
intPtr++;
}

cout<<"character array output: "<<endl;
for(int i = 0; i<SIZE; i++){
cout<<*charPtr<<" at "<<reinterpret_cast<unsigned long>(charPtr)<<endl;
charPtr++;
}
}

输出结果如下：

intager array output: 
1 at 140729290089744
2 at 140729290089748
3 at 140729290089752
4 at 140729290089756
5 at 140729290089760
character array output: 
F at 140729290089776
i at 140729290089777
s at 140729290089778
C at 140729290089779
o at 140729290089780

四，结构体

(1) 结构体创建和使用

[code]void tryStruct() {
struct Student {
string name;
int age;
char gender;
};

//第一种方式，赋值one by one
Student stu1;
stu1.name = "Sessy";
stu1.age = 19;
stu1.gender = 'F';
cout<<"student1 info: "<<endl;
cout<<"+name: "<<stu1.name<<endl;
cout<<"+age: "<<stu1.age<<endl;
cout<<"+gender: "<<stu1.gender<<endl;

cout<<"-----------------------"<<endl;

//第二种方式，like 数组
Student stu2 = {"John", 18, 'M'};
cout<<"student2 info: "<<endl;
cout<<"+name: "<<stu1.name<<endl;
cout<<"+age: "<<stu1.age<<endl;
cout<<"+gender: "<<stu1.gender<<endl;
}

上图可以看到用"结构体变量.结构体成员"的方式来访问结构体成员；

(2) 用指针访问结构体成员

[code]	Student *pStu = &stu2;
cout<<"get struct info with pointer: "<<endl;
cout<<"+name:"<<pStu->name<<endl;
cout<<"+age:"<<pStu->age<<endl;
cout<<"+gender:"<<pStu->gender<<endl;

五，传值，传址，传引用

(1) 传值

默认情况下，参数只能以值传递的方式给函数，也就是说被传递到函数的只是变量的值，不是变量本身．

[code]int main() {
int aa = 11, bb = 22;
trySwapByValue(aa, bb);
cout<<"aa == "<<aa<<", bb == "<<bb<<endl;
return 0;
}

void trySwapByValue(int a, int b) {
int temp = a;
b = a;
a = temp;
}

aa, bb将自己的值传给函数的参数a, b之后就和aa, bb没关系了．所以trySwapByValue里面再热闹，也跟aa, bb无关． 

(2) 传地址

[code]int main() {
int aa = 11, bb = 22;
trySwapByAddress(&aa, &bb);
cout<<"aa == "<<aa<<", bb == "<<bb<<endl;
return 0;
}

void trySwapByAddress(int *a, int *b) {
int temp = *b; //将b的地址暂存到temp
*b = *a;       //指针b指向a的地址
*a = temp;     //指针a指向b的地址
}

输出结果：aa == 22, bb == 11
成功交换了aa和bb 

(3) 传引用

[code]int main() {
int aa = 11, bb = 22;
trySwapByReference(aa, bb);
cout<<"aa == "<<aa<<", bb == "<<bb<<endl;
return 0;
}

//为何称为传引用呢？－－可能因为变量名被称为引用？
void trySwapByReference(int &a, int &b) {
int temp = b;
b = a;
a = temp;
}

输出结果：aa == 22, bb == 11
成功交换了aa和bb

六，对象

小demo一个：

[code]#include <iostream>
using namespace std;

#define FULL_GAS 81
class Car {
public:
string color;
string engine;
unsigned int gas_tank;
unsigned int wheel;

Car(void);
void setColor(string color);
void setEngine(string engine);
void setWheel(unsigned int w);
void fillTank(int liter);
int running(void);
void warning(void);
};

//constructor
Car::Car(void) {
color = "Red";
engine = "V8";
wheel = 4;
gas_tank = FULL_GAS;
}

void Car::setColor(string col) {
color = col;
}

void Car::setEngine(string eng) {
engine = eng;
}

void Car::setWheel(unsigned int w) {
wheel = w;
}

void Car::fillTank(int liter) {
gas_tank += liter;
}

int Car::running(void) {
cout<<"I'm running at a high speed"<<endl;
gas_tank--;
cout<<"gas left: "<<100*gas_tank/FULL_GAS<<"%"<<endl;
return gas_tank;
}

void Car::warning(void) {
cout<<"WARNING!"<<endl;
cout<<100*gas_tank/FULL_GAS<<"% oil in tank"<<endl;
}

int main() {
char i;
Car mCar;
mCar.setColor("Yellow");
mCar.setEngine("V8");
mCar.setWheel(4);
mCar.gas_tank = FULL_GAS;

while(mCar.running()) {
if(mCar.running() < 10) {
mCar.warning();
cout<<"Need to add oil?(Y/N)"<<endl;
cin>>i;
if('Y' == i || 'y' == i){
mCar.fillTank(FULL_GAS);
}
}
}
return 0;
}