CH8 课后习题

8.1和8.2

 #include <iostream>

 using namespace std;

 istream& f(istream& in)
 {
     int v;
     in >> v;
     if (in.bad())
         throw runtime_error("IO is bad");
     if (in.fail())
     {
         cerr << "bad data,try again" << endl;
         in.clear();
         in.ignore(, '\n');
         //忽略的知识点continue只能用在循环中
     }
     cout << v << endl;
     in.clear();
     return in;
 }
 int main()
 {
     cout << "please enter numbers:(Ctrl+Z to end)" << endl;
     f(cin);//cin遇到空格会结束，如果要读取整行，可以使用getline
     system("pause");
     return ;
 }

8.3

遇到了文件结束符标志，或者是输入错误的流或无效数据

8.4

 #include <iostream>
 #include <vector>
 #include <string>
 #include <fstream>

 using namespace std;

 int main()
 {
     string fileName;
     cout << "please enter the name of file:" << endl;
     cin >> fileName;
     ifstream infile(fileName);
     if (!infile)
     {
         cerr << "can not open the file you entered,please check!" << endl;
         return -;
     }
     string line;
     vector<string> row;
     while (getline(infile, line))
     {
         row.push_back(line);
     }
     for (auto it : row)
         cout << it << endl;

     system("pause");
     return ;
 }

8.5

将8.4的第21行改为while(infile>>line)即可

8.9

 #include <iostream>
 //#include <vector>
 #include <sstream>
 #include <string>

 using namespace std;

 istream& f(istream& in)
 {
     string str;

     //in >> str;//遇到空格就结束，使用循环
     while (in >> str, !in.eof())
     {
         if (in.bad())
             throw runtime_error("IO IS bad!");
         if (in.fail())
         {
             cerr << "bad data or not matched" << endl;
             in.clear();
             in.ignore(, '\n');
             continue;
         }
         cout << str << endl;
     }

 }

 int main()
 {
     ostringstream os;
     os << "Hello C++" << endl;;
     istringstream in(os.str());
     f(in);
     system("pause");
     return ;
 }

8.10

 #include <iostream>
 #include <sstream>
 #include <vector>
 #include <string>
 #include <fstream>

 using namespace std;

 int main()
 {
     string fileName;
     cout << "please enter the name of the file:" << endl;
     cin >> fileName;
     ifstream infile(fileName);
     if (!infile)
     {
         cerr << "can not open the file" << endl;
         return -;
     }

     string line;
     vector<string>txt_row;
     while (getline(infile, line))
     {
         txt_row.push_back(line);
         //istringstream record(line);//题目要求从vector中读取数据，不是从文件，所以这样不符合要求
     }
     infile.close();
     for (auto it : txt_row)
     {
         istringstream line_str(it);
         string word;
         while (line_str >> word)
             cout << word << " ";
         cout << endl;

     }
     system("pause");
     return ;
 }

8.11

istringstream 的对象record若定义在while循环外，则会被循环调用，重复使用流，需要恢复流状态，使用clear恢复

 #include <iostream>
 #include <vector>
 #include <sstream>

 using namespace std;
 struct PersonInfo {
     string name;
     vector<string>phone;

 };

 int main()
 {

     string line;
     string word;
     vector<PersonInfo>person;
     istringstream record;
     while (getline(cin, line))
     {
         PersonInfo info;
         record.clear();
         record >> info.name;
         while (record >> word)
         {
             info.phone.push_back(word);

         }
         person.push_back(info);
     }
     system("pause");
     return ;
 }

8.12

因为每个人的电话号码数量不固定。

8.13

此题，我写的存在问题，测试时和我的文件分别是这样的

 #include <iostream>
 #include <fstream>
 #include <sstream>
 #include <vector>

 using namespace std;

 struct PersonInfo {
     string name;
     vector<string>phone;
 };

 bool valid(const string& str)
 {
     cout << "check the string valid or not" << endl;
     return true;
 }

 //string format(string& str)
 string format(const string& str)
 {
     cout << "format the phone numbers " << endl;
     return str;
 }
 int main(int argc,char*argv[])
 {
     string line;
     string word;
     vector<PersonInfo> person;
     istringstream record;
     if (argc != )
     {
         cerr << "please enter the name of file." << endl;
         return -;
     }
     ifstream infile(argv[]);
     if (!infile)
     {
         cerr << "can not open the file" << endl;
         return -;
     }
     while (getline(infile, line))
     {
         PersonInfo info;
         infile.clear();
         record.str(line);
         record >> info.name;

         while (record >> word)
         {
             info.phone.push_back(word);
         }
         person.push_back(info);
     }

     //实现将从文件读取的记录输出
     ostringstream  os;
     for (const auto& entry : person)
     {
         ostringstream badNums;
         ostringstream formatted;
         for (auto &nums : entry.phone)
         {
             if (!valid(nums))
             {
                 //badNums << nums << "  is invalid" << endl;
                 badNums << " " << nums;

             }
             else
                 //formatted << "after foramtted:  " << format(nums) << endl;
                 formatted << " " << format(nums);
         }

         if (badNums.str().empty())
             os << entry.name << " " << formatted.str() << endl;
         else
             cerr << "input error,try again" << endl;

     }
     cout << os.str() << endl;//
     //system("pasue");
     return ;
 }

另外，我认为format函数的参数应该是非const 型的，但是若是非const型，则62行就不能是引用型，否则编译出错，我暂时还没想明白原因

8.14

如上，使用引用是因为person和phone的元素分别是struct和string对象，使用引用可避免拷贝，但是教材中定义为const，我就无法理解了，通常定义为const是避免改变这些项的值，name成员不能改变，可是phone成员需要格式化处理，需要改变