类型转换和io流

旧城等待， 2022-06-11 09:21 191阅读 0赞

//C++类型转换
    //static_cast 普遍情况
    //const_cast 去常量
    //dynamic_cast 子类类型转为父类类型
    //reinterpret_cast 函数指针转型，不具备移植性
    
    //原始类型转换，所有情况都是一种写法，可读性不高，有可能有潜在的风险
    
    /*
    void* func(int type){	
    	switch (type){
    	case 1:	{
    				int i = 9;
    				return &i;
    	}
    	case 2:	{
    				int a = 'X';
    				return &a;
    	}
    	default:{
    				return NULL;
    	}
    
    	}	
    }
    
    void func2(char* c_p){
    	cout << *c_p << endl;
    }
    
    void main(){	
    	//int i = 0;
    	//自动转换
    	//double d = i;
    	//double d = 9.5;
    	//int i = d;
    
    	//int i = 8;
    	//double d = 9.5;
    	//i = static_cast<int>(d);
    	
    	//void* -> char*
    	//char* c_p = (char*)func(2);
    	//char* c_p = static_cast<char*>(func(2));
    
    	//C++ 意图明显
    	func2(static_cast<char*>(func(2)));
    	//C
    	func2((char*)(func(2)));
    	
    	system("pause");
    }
    */
    
    
    /*
    void func(const char c[]){
    	//c[1] = 'a';
    	//通过指针间接赋值
    	//其他人并不知道，这次转型是为了去常量
    	//char* c_p = (char*)c;
    	//c_p[1] = 'X';
    	//提高了可读性
    	char* c_p = const_cast<char*>(c);
    	c_p[1] = 'Y';
    
    	cout << c << endl;
    }
    
    void main(){
    	char c[] = "hello";
    	func(c);
    
    	system("pause");
    }
    */
    
    /*
    class Person{
    public:
    	virtual void print(){
    		cout << "人" << endl;
    	}
    };
    
    class Man : public Person{
    public:
    	void print(){
    		cout << "男人" << endl;
    	}
    
    	void chasing(){
    		cout << "泡妞" << endl;
    	}
    };
    
    
    class Woman : public Person{
    public:
    	void print(){
    		cout << "女人" << endl;
    	}
    
    	void carebaby(){
    		cout << "生孩子" << endl;
    	}
    };
    
    void func(Person* obj){	
    
    	//调用子类的特有的函数，转为实际类型
    	//并不知道转型失败
    	//Man* m = (Man*)obj;
    	//m->print();
    
    	//转型失败，返回NULL
    	Man* m = dynamic_cast<Man*>(obj);	
    	if (m != NULL){
    		m->chasing();
    	}
    
    	Woman* w = dynamic_cast<Woman*>(obj);
    	if (w != NULL){
    		w->carebaby();
    	}
    }
    
    void main(){
    	
    	//Woman w1;
    	//Person *p1 = &w1;
    
    	//func(p1);
    
    	Woman w1;
    	Woman* w_p = &w1;
    	
    
    	system("pause");
    }
    */
    
    /*
    void func1(){
    	cout << "func1" << endl;
    }
    
    char* func2(){
    	cout << "func2" << endl;
    	return "abc";
    }
    
    typedef void(*f_p)();
    
    void main(){
    	//函数指针数组
    	f_p f_array[6];
    	//赋值
    	f_array[0] = func1;
    
    	//C方式
    	//f_array[1] = (f_p)(func2);
    	//C++方式
    	f_array[1] = reinterpret_cast<f_p>(func2);
    
    	f_array[1]();
    
    	system("pause");
    }
    
    */
    
    #include <fstream>
    
    //IO流
    //文本文件操作
    /*
    void main(){
    	char* fname = "c://dest.txt";
    	//输出流
    	ofstream fout(fname);
    	//创建失败
    	if (fout.bad()){ 
    		return;
    	}
    
    	fout << "jack" << endl;
    	fout << "rose" << endl;
    	
    	//关闭
    	fout.close();
    
    	//读取
    	ifstream fin(fname);
    	if (fin.bad()){
    		return;
    	}
    	char ch;
    	while (fin.get(ch)){
    		//输出
    		cout << ch;
    	}
    	fin.close();
    
    	system("pause");
    }
    */
    
    //二进制文件
    /*
    void main(){
    	char* src = "c://src.jpg";
    	char* dest = "c://dest.jpg";
    
    	//输入流
    	ifstream fin(src, ios::binary);
    	//输出流
    	ofstream fout(dest, ios::binary);
    
    	if (fin.bad() || fout.bad()){
    		return;
    	}
    
    	while (!fin.eof()){
    		//读取
    		char buff[1024] = {0};
    		fin.read(buff,1024);
    
    		//写入
    		fout.write(buff,1024);
    	}
    
    	//关闭
    	fin.close();
    	fout.close();
    
    	system("pause");
    }
    */
    
    /*
    //C++对象的持久化
    class Person
    {
    public:
    	Person()
    	{
    
    	}
    	Person(char * name, int age)
    	{
    		this->name = name;
    		this->age = age;
    	}
    	void print()
    	{
    		cout << name << "," << age << endl;
    	}
    private:
    	char * name;
    	int age;
    };
    
    
    void main()
    {
    	Person p1("柳岩", 22);
    	Person p2("rose", 18);
    	//输出流
    	ofstream fout("c://c_obj.data", ios::binary);
    	fout.write((char*)(&p1), sizeof(Person)); //指针能够读取到正确的数据，读取内存区的长度
    	fout.write((char*)(&p2), sizeof(Person));
    	fout.close();
    
    	//输入流
    	ifstream fin("c://c_obj.data", ios::binary);
    	Person tmp;
    	fin.read((char*)(&tmp), sizeof(Person));
    	tmp.print();
    
    	fin.read((char*)(&tmp), sizeof(Person));
    	tmp.print();
    
    	system("pause");
    
    }
    */
    
    
    //stl standard template library 标准模板库
    //util
    //c++ 集合-> java 集合
    
    #include <string>
    
    /*
    void main()
    {
    	string s1 = "craig david";
    	string s2(" 7 days");
    	string s3 = s1 + s2;
    
    	cout << s3 << endl;
    	
    	//转c字符串
    	const char* c_str = s3.c_str();
    	cout << c_str << endl;
    
    	//s1.at(2);
    
    
    	system("pause");
    }
    */
    
    //容器
    #include <vector>
    
    void main()
    {
    	//动态数组
    	//不需要使用动态内存分配，就可以使用动态数组
    	vector<int> v;
    	v.push_back(12);
    	v.push_back(10);
    	v.push_back(5);
    
    	for (int i = 0; i < v.size(); i++)
    	{
    		cout << v[i] << endl;
    	}
    
    	system("pause");
    }