8.1和8.2
1 #include <iostream>
2
3 using namespace std;
4
5 istream& f(istream& in)
6 {
7 int v;
8 in >> v;
9 if (in.bad())
10 throw runtime_error("IO is bad");
11 if (in.fail())
12 {
13 cerr << "bad data,try again" << endl;
14 in.clear();
15 in.ignore(100, ‘\n‘);
16 //忽略的知识点continue只能用在循环中
17 }
18 cout << v << endl;
19 in.clear();
20 return in;
21 }
22 int main()
23 {
24 cout << "please enter numbers:(Ctrl+Z to end)" << endl;
25 f(cin);//cin遇到空格会结束，如果要读取整行，可以使用getline
26 system("pause");
27 return 0;
28 }
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
1 #include <iostream>
2 #include <vector>
3 #include <string>
4 #include <fstream>
5
6 using namespace std;
7
8 int main()
9 {
10 string fileName;
11 cout << "please enter the name of file:" << endl;
12 cin >> fileName;
13 ifstream infile(fileName);
14 if (!infile)
15 {
16 cerr << "can not open the file you entered,please check!" << endl;
17 return -1;
18 }
19 string line;
20 vector<string> row;
21 while (getline(infile, line))
22 {
23 row.push_back(line);
24 }
25 for (auto it : row)
26 cout << it << endl;
27
28 system("pause");
29 return 0;
30 }
8.5
将8.4的第21行改为while(infile>>line)即可
8.9
1 #include <iostream>
2 //#include <vector>
3 #include <sstream>
4 #include <string>
5
6 using namespace std;
7
8 istream& f(istream& in)
9 {
10 string str;
11
12 //in >> str;//遇到空格就结束，使用循环
13 while (in >> str, !in.eof())
14 {
15 if (in.bad())
16 throw runtime_error("IO IS bad!");
17 if (in.fail())
18 {
19 cerr << "bad data or not matched" << endl;
20 in.clear();
21 in.ignore(100, ‘\n‘);
22 continue;
23 }
24 cout << str << endl;
25 }
26
27
28 }
29
30 int main()
31 {
32 ostringstream os;
33 os << "Hello C++" << endl;;
34 istringstream in(os.str());
35 f(in);
36 system("pause");
37 return 0;
38 }
8.10
1 #include <iostream>
2 #include <sstream>
3 #include <vector>
4 #include <string>
5 #include <fstream>
6
7 using namespace std;
8
9 int main()
10 {
11 string fileName;
12 cout << "please enter the name of the file:" << endl;
13 cin >> fileName;
14 ifstream infile(fileName);
15 if (!infile)
16 {
17 cerr << "can not open the file" << endl;
18 return -1;
19 }
20
21 string line;
22 vector<string>txt_row;
23 while (getline(infile, line))
24 {
25 txt_row.push_back(line);
26 //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
27 }
28 infile.close();
29 for (auto it : txt_row)
30 {
31 istringstream line_str(it);
32 string word;
33 while (line_str >> word)
34 cout << word << " ";
35 cout << endl;
36
37 }
38 system("pause");
39 return 0;
40 }
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
1 #include <iostream>
2 #include <vector>
3 #include <sstream>
4
5 using namespace std;
6 struct PersonInfo {
7 string name;
8 vector<string>phone;
9
10 };
11
12 int main()
13 {
14
15 string line;
16 string word;
17 vector<PersonInfo>person;
18 istringstream record;
19 while (getline(cin, line))
20 {
21 PersonInfo info;
22 record.clear();
23 record >> info.name;
24 while (record >> word)
25 {
26 info.phone.push_back(word);
27
28 }
29 person.push_back(info);
30 }
31 system("pause");
32 return 0;
33 }
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
1 #include <iostream>
2 #include <fstream>
3 #include <sstream>
4 #include <vector>
5
6 using namespace std;
7
8 struct PersonInfo {
9 string name;
10 vector<string>phone;
11 };
12
13 bool valid(const string& str)
14 {
15 cout << "check the string valid or not" << endl;
16 return true;
17 }
18
19 //string format(string& str)
20 string format(const string& str)
21 {
22 cout << "format the phone numbers " << endl;
23 return str;
24 }
25 int main(int argc,char*argv[])
26 {
27 string line;
28 string word;
29 vector<PersonInfo> person;
30 istringstream record;
31 if (argc != 2)
32 {
33 cerr << "please enter the name of file." << endl;
34 return -1;
35 }
36 ifstream infile(argv[1]);
37 if (!infile)
38 {
39 cerr << "can not open the file" << endl;
40 return -1;
41 }
42 while (getline(infile, line))
43 {
44 PersonInfo info;
45 infile.clear();
46 record.str(line);
47 record >> info.name;
48
49 while (record >> word)
50 {
51 info.phone.push_back(word);
52 }
53 person.push_back(info);
54 }
55
56 //实现将从文件读取的记录输出
57 ostringstream os;
58 for (const auto& entry : person)
59 {
60 ostringstream badNums;
61 ostringstream formatted;
62 for (auto &nums : entry.phone)
63 {
64 if (!valid(nums))
65 {
66 //badNums << nums << " is invalid" << endl;
67 badNums << " " << nums;
68
69 }
70 else
71 //formatted << "after foramtted: " << format(nums) << endl;
72 formatted << " " << format(nums);
73 }
74
75 if (badNums.str().empty())
76 os << entry.name << " " << formatted.str() << endl;
77 else
78 cerr << "input error,try again" << endl;
79
80 }
81 cout << os.str() << endl;//
82 //system("pasue");
83 return 0;
84 }
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
时间： 2024-10-25 18:51:05