C++Primer fifth edition exercise answers [Chapter 8]

C++Primer Fifth Edition Exercise Answers [General List]: https://blog.csdn.net/Dust_Evc/article/details/114334124

8.1 + 8.2

#include <iostream>
#include <string>

using std::cout;
using std::cin;
using std::endl;
using std::istream;
using std::string;


int main()
{
	istream& func(istream &is);
	istream& is = func(cin);
	cout << is.rdstate() << endl;	//返回流is的当前条件状态
	return 0; 
}

istream& func(istream &is)
{
	string buf;
	while (is >> buf)
		cout << buf << endl;
	is.clear();  //复位流is的状态
	return is;
}

8.3

If any one of `badbit`, `failbit`, and `eofbit` is set, then the condition to check the flow status will fail.     

8.4

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

using namespace std;

int main()
{
	void ReadFileToVec(const string& fileName, vector<string>& vec);

	vector<string> ABC;
	ReadFileToVec("input.txt", ABC);  //此input.txt自己创建一个，随便输些内容，放在项目路径下
	
	for (auto str : ABC) //利用范围for语句输出Vector ABC中的值
		cout << str << endl;

	ofstream fout("output.txt");
	streambuf *coutbackup;
	coutbackup = cout.rdbuf(fout.rdbuf()); //用 rdbuf() 重定向  
	for (auto str : ABC) //利用范围for语句将Vector ABC中的值输出至文件output.txt
		cout << str << endl;

	return 0;

}


void ReadFileToVec(const string& fileName, vector<string>& vec) //使用引用，直接更改ABC中的值
{
	ifstream ifs(fileName); //定义文件输入流 ifs，它从string类型、名为fileName的文件读取数据
	if (ifs)
	{
		string buf;
		while (getline(ifs, buf))
			vec.push_back(buf);
	}
}

8.5

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

using namespace std;

int main()
{
	void ReadFileToVec(const string& fileName, vector<string>& vec);

	vector<string> ABC;
	ReadFileToVec("input.txt", ABC);

	for (auto str : ABC) //利用范围for语句输出Vector ABC中的值
		cout << str << endl;

	ofstream fout("output.txt", ofstream::app);  //与Ex_8.4相比，添加ofstream::app，可以保留output.txt中的已有数据
	streambuf *coutbackup;
	coutbackup = cout.rdbuf(fout.rdbuf()); //用 rdbuf() 重定向 
	for (auto str : ABC) //利用范围for语句将Vector ABC中的值输出至文件output.txt
		cout << str << endl; 

	return 0;

}

void ReadFileToVec(const string& fileName, vector<string>& vec)  //使用引用，直接更改ABC中的值
{
	ifstream ifs(fileName);		//定义文件输入流 ifs，它从string类型、名为fileName的文件读取数据
	if (ifs)
	{
		string buf;
		while (ifs >> buf)		//【注意】：直接ifs >> buf既可实现逐单词读取
			vec.push_back(buf);
	}
}

8.6

P284 page is exactly the same

8.7

Take the output file name as the second parameter, which is argv[2]

fstream out(argv[2])

8.8

File mode, specify how to use after opening the file, app mode (append) is positioned to the end of the file

ofstream out("file",ofstream::app);//定位到文件结尾，保存文件中的已有数据

8.9

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

using namespace std;

int main()
{
	istream& func(istream &is);

	string line;
	while (getline(cin, line))
	{
		istringstream record(line);	 // 将record绑定至刚读入的一行数据
		cout << "数据逐单词输出为为：" << endl;
		istream& is = func(record);
		cout << "流is的当前条件状态为：" << is.rdstate() << endl;	//返回流is的当前条件状态
	}	
	return 0;
}

istream& func(istream &is)
{
	string buf;
	while (is >> buf)
		cout << buf << endl;
	is.clear();  //复位流is的状态
	return is;
}

8.10

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

using namespace std;

int main()
{
	ifstream ifstrm("input.txt");	//此input.txt自己创建一个，随便输些内容，放在项目路径下
	if (!ifstrm)	//检查文件是否打开成功
	{
		cerr << "No data!?" << endl;
		return -1;
	}

	vector<string> VEC;
	string temp;
	while(getline(ifstrm, temp))	//将input.txt文件中的数据逐行读取，并写入字符串向量VEC中
		VEC.push_back(temp);

	void Read_Wordly(vector<string>& it);
		Read_Wordly(VEC);		
	return 0;
}

void Read_Wordly(vector<string>& it)	//定义利用istringstream逐单词读取字符串向量的函数
{
	for (auto readline : it)	//利用范围for语句先读取字符串向量中各字符串元素
	{
		istringstream istr(readline);	//定义名为istr的字符串读取流，并指向readline字符串
		string temp;
		while (istr >> temp)    //将istr指向的字符串逐单词输出
			cout << temp << " >> ";
		cout << endl;
		istr.clear();
		cout << "字符串读取流的当前条件状态为：" << istr.rdstate() << endl;	//返回流的当前条件状态
	}
}

8.11

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

using namespace std;

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

int main()
{
	string line, word;
	vector<PersonInfo> people;
	istringstream record;
	while (getline(cin, line))
	{
		PersonInfo info;
		record.clear();
		record.str(line);	//【关键】将string line拷贝到str中
		record >> info.name;
		while (record >> word)
			info.phones.push_back(word);
		people.push_back(info);
	}

	for (auto &p : people)
	{
		cout << p.name << " ";
		for (auto &s : p.phones)
			cout << s << " ";
		cout << endl;
	}

	return 0;
}

8.12

Because only the aggregation class is needed here, there is no need to use in-class initialization in PersionInfo.

8.13

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

using namespace std;

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

bool valid(const string& str)	
{
	return isdigit(str[0]);		//首字符不是数字则无效
}

string format(const string& str)	//号码格式化格式： 123-456-剩余字符，【因此，需要号码位数大于6位】
{
	return str.substr(0, 3) + "-" + str.substr(3, 3) + "-" + str.substr(6);
}

int main()
{
	ifstream ifs("sstream.txt");
	if (!ifs)
	{
		cerr << "no phone numbers?" << endl;
		return -1;
	}

	string line, word;
	vector<PersonInfo> people;
	istringstream record;
	while (getline(ifs, line))
	{
		PersonInfo info;
		record.clear();
		record.str(line);
		record >> info.name;
		while (record >> word)
			info.phones.push_back(word);
		people.push_back(info);
	}

	for (const auto &entry : people)
	{
		ostringstream formatted, badNums;
		for (const auto &nums : entry.phones)
		{
			if (!valid(nums))
				badNums << " " << nums;
			else
				formatted << " " << format(nums);	//号码格式化
		}
		if (badNums.str().empty())
			cout << entry.name << " " << formatted.str() << endl;	//输出名字及格式化的号码
		else
			cerr << "input error: " << entry.name
			<< " invalid number(s) " << badNums.str() << endl;
	}

	return 0;
}

8.14

* They are all class types, so use references to avoid copying.
* They will not change their values ​​in the loop, so use const.