C++ Primer Plus 学习笔记第十六章 string类

痛定思痛。 2022-10-01 13:43 201阅读 0赞

string类的构造函数

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvdWx3eWI_size_16_color_FFFFFF_t_70][]

构造函数程序示例：

#include <iostream>
    #include <string>
    
    int main()
    {
      using namespace std;
      string one("Lottery Winner!");
      cout << one << endl;
      string two(20, '$');
      cout << two << endl;
      string three(one);
      cout << three << endl;
      one += " Oops!";
      cout << one << endl;
      two = "Sorry! That was ";
      three[0] = 'P';
      string four;
      four = two + three;
      cout << four << endl;
      char alls[] = "All's well that ends well";
      string five(alls, 20);
      cout << five << "!\n";
      string six(alls + 6, alls + 10);
      cout << six << ", ";
      string seven(&five[6], &five[10]);
      cout << seven << "...\n";
      string eight(four, 7, 16);
      cout << eight << " in motion!" << endl;
      return 0;
    }

![20190612130713542.png][]

string类输入：

C-风格的字符串输入：

char info\[100\];

cin >> info;

cin.getline(info, 100);

cin.get(info, 100);

对于string对象：

string stuff;

cin >> stuff;

getline(cin, stuff);

指定边界：

c-string: cin.getline(info, 100, ':');

getline(stuff, ':')

string的getline自动调整大小。而c-风格的不行

string对象的最大长度是由string::npos指定的，通常是unsigned int值

![20190612132226779.png][]

![20190612132233110.png][]

string的 operator>>()

![2019061213251214.png][]

文件读取示例：

#include <iostream>
    #include <fstream>
    #include <string>
    #include <cstdlib>
    
    int main()
    {
      using namespace std;
      ifstream fin;
      fin.open("tobuy.txt");
      if (fin.is_open() == false)
      {
        cerr << "Can't open file. Bye.\n";
        exit(EXIT_FAILURE);
      }
      string item;
      int count = 0;
      getline(fin, item, ':');
      while (fin)
      {
        ++count;
        cout << count << ": " << item << endl;
        getline(fin, item, ':');
      }
      cout << "Done\n";
      fin.close();
      return 0;
    }

tobuy.txt：

sardines:chocolate ice cream:pop corn:leeks:
    cottage cheese:olive oil:butter:tofu:

输出结果

![20190612134630937.png][]

![20190612134727713.png][]

先完结

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvdWx3eWI_size_16_color_FFFFFF_t_70]: /images/20220118/c8abbbcb279a445b9e84ffc60a825e10.png
[20190612130713542.png]: /images/20220118/cca410e18cbb44dd85e5ca4988412f4c.png
[20190612132226779.png]: /images/20220118/35ce8b8bf65a49b5b05a4a394528889f.png
[20190612132233110.png]: /images/20220118/1ebc9e2d7a014b4d92bb3da1ce1f994f.png
[2019061213251214.png]: /images/20220118/bd882805cfcd4337a010990afa7d3f3b.png
[20190612134630937.png]: /images/20220118/f640c190a9ed4d67bce171decb9b6efc.png
[20190612134727713.png]: /images/20220118/c855478a02b94d73bb6073fe9a50abc4.png