C++随笔

#include <windows.h>
#include <iostream>
#include <stdio.h>
#include <string>
#include <cstring>
#include <cctype>

#include <initializer_list>        //函数可变参数模板.和vector类似
#include <cassert>                //assert()的头文件

//STL
#include <stack>    //堆栈
#include <map>        //字典
#include <list>        //链表
#include <vector>    //数组
#include <queue>    //队列
#include <deque>    //动态数组


using namespace std;

typedef struct listNode                    //节点对象
{
    //1.数据域
    int data;


    //2.链接域 or 指针域
    struct listNode *link;
}node;


node *create3()//创建3个节点的链表
{
    node *first, *second, *third;

    first = (node *)malloc(sizeof(node));//给第1个节点分配内存空间,并且指针转换
    second = (node *)malloc(sizeof(node));
    third = (node *)malloc(sizeof(node));

    third->link = NULL;//最后1个元素的地址应该是null
    third->data = 30;
    second->link = third;
    second->data = 20;
    first->link = second;
    first->data = 10;


    return first;
}


//测试编译器的一些函数相关东西
void CompilerTest()
{
#ifndef NDEBUG
    cerr << __FUNCDNAME__ << endl;
    cerr << __FUNCTION__ << endl;
    cerr << __FILE__ << endl;//文件路径
    cerr << __LINE__ << endl;
    cerr << __TIME__ << endl;
    cerr << __TIMESTAMP__ << endl;
    cerr << __DATE__ << endl;

    cout << "这些信息通常都可以作为log的辅助信息" << endl;
#endif
}



void show_Test()
{
    node *list = create3();

    cout << list->link->link->data << endl;


    while (NULL != list)
    {
        cout << list->data << endl;
        list = list->link;
    }

    delete list;
    list = NULL;
}

//初始化次数
size_t count_calls()
{
    static size_t ctr = 0;//不再经过 这一句
    return ++ctr;
}



//可变形参
void error_msg(initializer_list<int> ilist)
{
    auto beg = ilist.begin();
    auto end = ilist.end();

    while (beg != end)
    {
        cout << *beg << "  "<<endl;
        ++beg;
    }
}


//不可以返回函数内部的定义的  引用和指针...,卧槽,可以的哦 流弊了
int& func()
{

    int a = 10;
    int &r = a;
    return r;

}

//返回类型是左值的函数可以写在 = 的左边
char& get_val(string &str, string::size_type ix)
{
    return str[ix];
}


//测试 assert()函数
void AssertTest()
{
    int x = 10;
    assert(!x);

    return;
}

//范围for,与引用
void ForRange()
{
    vector<int> v;
    v.push_back(0);
    v.push_back(0);
    v.push_back(0);
    v.push_back(0);

    int i = 0;
    for (auto &r : v)
    {
        r = 1;
        cout << v[i] << endl;
    }
}

//getline
void GetLineTest()
{
    string line;
    while (getline(cin, line))
    {
        cout << line.size() << endl;
        cout << line.length() << endl;

        cout << line << endl;
    }
    getline(cin, line);
    cout << line << endl;

}



struct Student
{
    Student() = default;


};

class ObjectSize
{
public:
    int a;
    int b;
    int c;
    double d;


};

class Screen
{
public:
    typedef std::string::size_type pos;
    Screen() = default;

    Screen(pos ht, pos wd, char c) : height(ht), width(wd)
    {}

private:
    pos cursor = 0;    //暂时不明白这个地方为啥有值了呢????????????????????????????
    pos height = 0;
    pos width = 0;
    string contents;

};

//string size()  length()
void StringVar()
{
    string a = "abc";
    cout << a.length() << endl;
    

    string str("123456");
    auto len = str.size();
    cout << len << endl;




    string str2 = "panzhengming";
    for (auto c:str2)
    {
        cout << c << "  ";
    }
}

//迭代器会移动的
void MoveIter()
{
    const int sz = 10;
    int arr[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    auto pBegin = begin(arr);
    auto pEnd = end(arr);

    while (pBegin != pEnd)
    {
        cout << *pBegin << " ";
        pBegin++;
    }

    cout << endl;
    pBegin = begin(arr);
    pEnd = end(arr);
    while (pBegin != pEnd)
    {
        *pBegin = 0;

        pBegin++;
    }

    pBegin = begin(arr);
    pEnd = end(arr);
    while (pBegin != pEnd)
    {
        cout << *pBegin << " ";
        pBegin++;
    }
}

//迭代器的用法
void Iter1()
{
    int arr[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
    vector<int> ivec(begin(arr), end(arr));
    auto Iter = ivec.begin();
    while (Iter != ivec.end())
    {
        cout << *Iter << " ";

        Iter++;
    }
}

//for语句的第1个表达式只执行1次初始化!!!
void ForExp1()
{
    vector<int> iver;
    iver.push_back(0);
    iver.push_back(0);
    iver.push_back(0);
    iver.push_back(0);

    for (int i = 0, sz = iver.size(); i != sz; i++)                
    {
        iver.push_back(iver[i]);
        cout << "hello" << endl;
        cout << sz << endl;
    }
    cout << iver.size() << endl;
}

//位操作
void BitTest()
{
    int bits = 0233;
    cout << bits << endl;
    bits << 8;
    cout << bits << endl;
    bits >> 3;
    cout << bits << endl;
    bits = 0227;
    ~bits;
    cout << bits << endl;


}

//
void ForTest2()
{
    for (size_t i = 0; i != 10; ++i)
    {
        cout << count_calls() << endl;
    }
}

//函数返回值作为左值
void FuncValueAsLeft()
{
    string s = "hello world";
    get_val(s, 0) = 'a';                //函数返回左值
    cout << s << endl;
}



//指针转换
void CastPoint()
{
    //----------------------------------------------------------------1
    //double dval;
    //int ival;
    //int *p;
    //dval = p = 0;
    //----------------------------------------------------------------2

    //double dval = 10.1;    
    //void *p = &dval;
    //cout << &dval << "  " << p << endl;
    ////cout << *p << endl; 错误
    //double *dp = static_cast<double *>(p);
    //cout << dp << "  " << *dp << endl;

    //----------------------------------------------------------------3
    //int i = 110;
    //int *ip = &i;
    //char *pc = (char *)ip;
    //cout << ip << "  " << *pc << endl;

    //----------------------------------------------------------------4
    //int i = 10;
    //{
    //    int *p = &i;
    //    cout << *p << "1111"<<endl;
    //}
    //cout << *p << endl;
}

//检查对象大小
void TestObjectSize()
{
    cout << sizeof(ObjectSize) << endl;//内存空间大小
    ObjectSize tempObj;
    cout << sizeof(tempObj) << endl;
}

//const 练习
void ConstTest()
{
    //变量是可读可写的
    //常量是只读不可写的
    //const赋值时,左边的读写权限要 <= 右边的读写权限

    int x = 3;
    int y = 4;

    int const *p = &x;
    cout << *p << endl;
    x = 5;
    cout << *p << endl;

    //*p = 1; 错误 *p是常量

    int *const p2 = &x;
    cout << x << "," << *p2 << "," << p << endl;
    *p2 = 11;
    cout << x << "," << *p2 << "," << p << endl;
    //p2 = &y;  错误 p2是常量


    cout << "-------------------------" << endl;
    int b = 50;
    const int *p3 = &b;
    b = 39;
    cout << *p3 << endl;
    //*p3 = 100;

    cout << "-------------------------" << endl;
    int ii = 0;
    const int ci = 42;
    ii = ci;
    //ci = ii;
    cout << ii << "," << ci << endl;

    /*
        网上查的结果
        我理解的const是一种约定，是说我用了const就不会改变变量的值了，而其他人乱动我也没办法。
        我是不是可以简单理解为,顶层是指 自己 不变,底层是指 所指向的 对象不变

        1, 只有在使用指针的时候我们才说const分为 顶层(top)const 和 底层(bottom)const.
        2, 右值引用你还用const你有毒吧.
        3, 如果是两个指针之间相互拷贝其 底层(bottom)const 起到很关键的作用.

        https://my.oschina.net/SHIHUAMarryMe/blog/595409
    */
}


//stack 练习堆栈.被称为是 专业程序员使用的数据结构
void StackTest()
{
    stack<int, deque<int>>        a;
    stack<int, vector<int>>        b;
    stack<int, list<int>>        c;
    stack<int>                    d;

    d.push(25);
    d.push(10);
    d.push(1);
    d.push(5);

    cout << "一共有" << d.size() << "个数据" << endl;

    int x = d.top();//只看栈顶个,不删除数据
    d.pop();//删除栈顶

    x = d.top();
    d.pop();

    x = d.top();

    cout << d.size();


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

//队列 练习
void QueueTest()
{
    //queue不能使用vector的哦,不方便两端操作
    queue<int, deque<int>>  a;
    queue<int, list<int>>    b;

    queue<int> q;//默认是 deque<int>

    //队尾插入数据
    q.push(10);
    q.push(5);
    q.push(-1);
    q.push(20);

    cout << q.size() << endl;

    cout << "队首数据,但是不删除" << q.front() << endl;
    cout << "队尾数据,但是不删除" << q.back() << endl;

    //队首删除
    q.pop();
    cout << "队首数据,但是不删除" << q.front() << endl;
    cout << "队尾数据,但是不删除" << q.back() << endl;

    /*
        循环通过 while(q.size() != 0)   或者 while(q.empty() == false)

        stack和queue都没有迭代器,所以不能用Iter
        因为stack和queue只允许操作2端的数据,不可以操作中间的数据,所以没有Iter
    */
}


//STL动态数组 deque
void DequeTest()
{
    deque<int> a;

    //从尾部插入
    a.push_back(3);
    a.push_back(4);
    a.push_back(5);

    //从前面插入
    a.push_front(2);
    a.push_front(1);
    a.push_front(0);

    for (size_t nCount = 0; nCount < a.size();++nCount)
    {
        cout << a[nCount] << ",";
    }


    cout << endl;
    a.pop_front();//删除前面
    a.pop_back();//删除后面
    //for (auto Iter = a.begin(); a.begin() != a.end();++Iter)    //这个地方报错.暂时不知道原因
    //{
    //    cout << *Iter << ",";
    //}
    
}
int main()
{
    
    


/*
DequeTest();

QueueTest();

StackTest();

ConstTest();

CastPoint();

TestObjectSize();

error_msg({ 100, 200, 300 });//可变形参 列表

FuncValueAsLeft();

int a = func();//返回函数内的局部变量引用 ...  c++ primer认为这是错误的.....那我这里是不是代码写错了

AssertTest();// assert()函数类似  if()判断,false就弹出警告

CompilerTest();//log的辅助信息

show_Test();

ForTest2()

ForRange();

GetLineTest();

StringVar();

MoveIter();

Iter1();

ForExp1();

BitTest();

*/



    cout << endl;
    system("pause");
    return 0;
}