string

void test(){

    //创建一个空的string对象
    string str;

    //拷贝一个和已经存在的对象内容一模一样的新的对象
    string copy(str);

    //生成一个abc的字符串
    string str2("abc");

    //在str2中取下标1至2的字符串生成一个新的字符串
    string substr(str2, 1, 2); //"bc"

    //在字符串"123456789"中取前5个
    string str3("123456789", 5);//"12345"

    //生成一个有5个a的字符串
    string str4(5, ‘a‘);//aaaaa

    //单参构造的隐式类型转换, 相当于调用string str2("abcde");
    string str5 = "abcde";

}

void test(){
    string str = "123456";
    //范围for:  实际上是通过迭代器实现的
              //支持迭代器访问的自定义类型都可以支持范围for
    for (auto& ch : str){
        cout << ch << " ";
        ch = ‘a‘;
    }
    cout << endl << str << endl;
}

void test(){
    string str = "123456";
    for (int i = 0; i < str.size(); i++){
        cout << str[i] << " ";
        str[i] = ‘a‘;
    }
    cout << endl << str << endl;
}

void test(){
    string str;
    cout << str.size() << endl;   //0

    //resize: 修改有效字符的个数,不足的补‘\0‘,多的去掉
    str.resize(10);
    cout << str.size() << endl;   //0000000000
    string str2 = "123";
    cout << str2.size() << endl;   //123
    str2.resize(10);
    cout << str2.size() << endl;   //1230000000
    str2.resize(2);
    cout << str2.size() << endl;   //12

    //不足的位置填充a
    str2.resize(5, ‘a‘);    //12aaa 
    str2.resize(2, ‘b‘);     //12,减小不会填充
}

void test(){
    string str = "123";
    //有效字符的个数
    int a = str.size();   //3
    //空间的容量
    int b = str.capacity();  //15
    cout << a << ‘ ‘ << b << endl;

    str.resize(2);
    int a1 = str.size();   //2
     int b1 = str.capacity();   //15
    cout << a1 << ‘ ‘ << b1 << endl;

    str.resize(20);
    int a2 = str.size();   //20
    //自动增加容量
    int b2 = str.capacity();   //31
    cout << a2 << ‘ ‘ << b2 << endl;

    //reserve:修改容量,只能增加容量
    //不会影响size的大小
    str.reserve(60);
    int a3 = str.size();   //20
    int b3 = str.capacity();   //63
    cout << a3 << ‘ ‘ << b3 << endl;

    //设置减小容量,但程序运行中无法减小容量,只能增容
    str.reserve(10);
    int a4 = str.size();  //20
    int b4 = str.capacity();   //63
    cout << a4 << ‘ ‘ << b4 << endl;
}

void test(){
    string str = "123";
    //有效字符的个数
    int a = str.size();   //3
    //空间的容量
    int b = str.capacity();  //15
    cout << a << ‘ ‘ << b << endl;

    str.clear();
    int a1 = str.size();   //0
    int b1 = str.capacity();   //15
    cout << a1 << ‘ ‘ << b1 << endl;
}

void test(){
    string str;
    string str1 = "123";

    //+=操作,相当于尾插
    str += str1;  //123
    str += "abc";  //123abc
    str += ‘4‘;   //123abc4
    str.operator+=(‘5‘);  //123abc45 


    //append操作,追加,相当于尾插
    str.append(str1);    //123abc45123
       // 从str中下标为1的开始加一个字符 
    str.append(str1, 1, 1);  //123abc451232
    str.append("abc");   //123abc451232abc
       // 从123456中加前5个 
    str.append("123456",5);   //123abc451232abc12345
       //增加5个相同字符
    str.append(5,‘m‘);   //123abc451232abc12345mmmmm

    //使用迭代器
    str.append(str1.begin(), str1.end());  //123abc451232abc12345mmmmm123
    cout << str << endl;
}

void test(){
    string str;
    string str1 = "123";
    str.assign(str1);  //123
    str.assign(str1,1,1);  //2
    str.assign("abc");   //abc
    str.assign("abcd",2);   //ab
    str.assign(5,‘a‘);    //aaaaa
    str.assign(++str1.begin(),str1.end());  //23
}

void test(){
    string str1 = "123";
    string str2 = "abc";

    //在下标为0的位置插入str2
    str1.insert(0, str2);  //abc123

    //在下标为4的位置插入str2中下标为1之后的两个字符
    str1.insert(4, str2,1,2);  //abc1bc23

    //尾插abc
    str1.insert(str1.size(),"abc");  //abc1bc23abc

    //在下标为5的位置插入123456中的前4个字符
    str1.insert(5, "123456",4);  //abc1b1234c23abc


    str1.insert(str1.begin(),2,‘0‘); //00abc1b1234c23abc

    str1.insert(str1.end(), str2.begin(), str2.end());//00abc1b1234c23abcabc
    cout << str1 << endl;
}