練習8.1：考察如何管理流的狀態

1 istream& func(istream& is)
2 {
3     string buf;
4     while ( is>>buf ) cout<<buf<<endl;
5     is.clear();
6     return is;
7 }

練習8.2：考察同上

 1 #include<iostream>
 2 #include<string>
 3 using namespace std;
 4 
 5 istream& func(istream& is
 
)
 6 {
 7     string buf;
 8     while ( is>>buf ) cout<<buf<<endl;
 9     is.clear();
10     return is;
11 }
12 
13 int main()
14 {
15     istream& is=func(cin);
16     cout<<is.rdstate()<<endl;
17     return 0;
18 }

練習8.3：考察cin的錯誤狀態

輸入使得cin進入了錯誤狀態會導致循環終止。如：badbit,failbit,eofbit

練習8.4：考察文件流的使用

 1 #include<iostream>
 2 #include<fstream>
 3 #include<vector>
 4 #include<string>
 5 using namespace std;
 6 
 7 void ReadFileToVec(const string& fileName,vector<string>& vec)
 8 {
 9     ifstream ifs(fileName);
10     if ( ifs )
11     {
12         string
 
 buf;
13         while ( getline(ifs,buf) ) vec.push_back(buf);
14     }
15 }
16 
17 int main()
18 {
19     vector<string>vec;
20     ReadFileToVec("../date/book.txt",vec);
21     for ( const auto& i:vec ) cout<<i<<endl;
22     return 0; 
23 }

練習8.5：考察同上

 1 #include<iostream>
 2 #include<fstream>
 3 #include<vector>
 4 #include<string>
 5 using namespace std;
 6 
 7 void ReadFileToVec(const string& fileName,vector<string>& vec)
 8 {
 9     ifstream ifs(fileName);
10     if ( ifs )
11     {
12         string buf;
13         while ( ifs>>buf ) vec.push_back(buf);
14     }
15 }
16 
17 int main()
18 {
19     vector<string>vec;
20     ReadFileToVec("../date/book.txt",vec);
21     for ( const auto& i:vec ) cout<<i<<endl;
22     return 0; 
23 }

練習8.9：考察istringstream的使用

 1 #include<iostream>
 2 #include<string>
 3 #include<sstream>
 4 using namespace std;
 5 
 6 istream& func(istream& is)
 7 {
 8     string buf;
 9     while ( is>>buf ) cout<<buf<<endl;
10     is.clear();
11     return is;
12 }
13 
14 int main()
15 {
16     istringstream iss("hello world");
17     func(iss);
18     return 0;
19 }

練習8.10：考察同上

 1 #include<iostream>
 2 #include<vector>
 3 #include<string>
 4 #include<fstream>
 5 #include<sstream>
 6 using namespace std;
 7 
 8 void ReadFileToVec(const string& fileName,vector<string>& vec)
 9 {
10     ifstream ifs(fileName);
11     if ( ifs )
12     {
13         string line;
14         while ( getline(ifs,line) ) vec.push_back(line);
15     }
16 }
17 
18 int main()
19 {
20     vector<string>vec;
21     ReadFileToVec("../date/book.txt",vec);
22     for ( auto& s:vec )
23     {
24         istringstream iss(s);
25         string word;
26         while ( iss>>word ) cout<<word<<endl;
27     }
28     return 0; 
29 }

練習8.11：考察同上

在每次使用時需要先清楚原有內容，在重新拷貝

 1 #include<iostream>
 2 #include<sstream>
 3 #include<string>
 4 #include<vector>
 5 using namespace std;
 6 struct PersonInfo{
 7     string name;
 8     vector<string>phones;
 9 };
10 
11 int main()
12 {
13     string line,word;
14     vector<PersonInfo>people;
15     istringstream record;
16     while ( getline(cin,line) )
17     {
18         PersonInfo info;
19         record.clear();
20         record.str(line);
21         record>>info.name;
22         while ( record>>word ) info.phones.push_back(word);
23         people.push_back(info);
24     }
25 }

練習8.12：

參考網上答案：因為這裏我們需要聚合類，所以我們不需要使用類內初始化

練習8.13：三種流的綜合應用

 1 #include<iostream>
 2 #include<sstream>
 3 #include<string>
 4 #include<vector>
 5 #include<fstream>
 6 using namespace std;
 7 struct PersonInfo{
 8     string name;
 9     vector<string>phones;
10 };
11 
12 bool valid(const string& s)
13 {
14     return isdigit(s[0]);
15 }
16 
17 string format(const string& str)
18 {
19     return str.substr(0,3)+"-"+str.substr(3,3)+"-"+str.substr(6);
20 }
21 
22 int main()
23 {
24     ifstream ifs("../date/phonenumbers.txt");
25     if ( !ifs )
26     {
27         cerr<<"no phone numbers?"<<endl;
28         return -1;
29     }
30     string line,word;
31     vector<PersonInfo>people;
32     istringstream record;
33     while ( getline(ifs,line) )
34     {
35         PersonInfo info;
36         record.clear();
37         record.str(line);
38         record>>info.name;
39         while ( record>>word ) info.phones.push_back(word);
40         people.push_back(info);
41     }
42     for ( const auto& entry:people )
43     {
44         ostringstream formatted,badNums;
45         for ( const auto& nums:entry.phones )
46         {
47             if ( !valid(nums) ) badNums<<" "<<nums;
48             else formatted<<" "<<format(nums);
49         }
50         if ( badNums.str().empty() ) 
51         {
52             cout<<entry.name<<" "<<formatted.str()<<endl;
53         }
54         else
55         {
56             cerr<<"input error: "<<entry.name<<"invalid number(s)"<<badNums.str()<<endl;
57         }
58     }
59 }

練習8.14：

因為它們都是類不是內置類型，所以使用引用會更加高效

又因為它們在整個過程中並不需要修改，所以使用const

C++ Primer(第五版) 第八章：IO庫