C++Primer第五版——习题答案详解（七）

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习题答案目录：https://www.cnblogs.com/Mered1th/p/10485695.html

第8章 IO库

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练习8.1

istream &iofunc(istream &is) {
	string s;
	while (is >> s) {
		cout << s << endl;
	}
	is.clear();
	return is;
}

练习8.2

#include<iostream>
#include<string>
using namespace std;

istream &iofunc(istream &is) {
	string s;
	while (is >> s) {
		cout << s << endl;
	}
	is.clear();
	return is;
}

int main() {
	iofunc(cin);
	return 0;
}

练习8.3
badbit、failbit和eofbit任一个被置位，则检测流状态的条件会失败。

练习8.4

#include<iostream>
#include<string>
#include<fstream>
#include<vector>
using namespace std;

int fileToVector(string fileName,vector<string> &svec){
	ifstream inFile(fileName);
	if (!inFile) {
		return 1;
	}
	string s;
	while (getline(inFile, s)) {
		svec.push_back(s);
	}
	inFile.close();
	if (inFile.eof()) {
		return 4;
	}
	if (inFile.bad()) {
		return 2;
	}
	if (inFile.fail()) {
		return 3;
	}
}
int main() {
	vector<string> svec;
	string fileName, s;
	cout << "Enter fileName:" << endl;
	cin >> fileName;
	switch (fileToVector(fileName, svec))
	{
	case 1:
		cout << "error: can not open file: " << fileName << endl;
		return -1;
	case 2:
		cout << "error: system failure." << endl;
		return -1;
	case 3:
		cout << "error: read failure." << endl;
		return -1;
	}
	cout << "向量里面的内容：" << endl;
	for (vector<string>::iterator iter = svec.begin();iter != svec.end();++iter)
		cout << *iter << endl;
	return 0;
}

练习8.5

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

using namespace std;

int fileToVector(string fileName, vector<string>& svec) {
	ifstream inFile(fileName.c_str());
	if (!inFile) {
		return 1;
	}
	string s;

	//习题8.4一次输入一行
	//while (getline(inFile, s)) {
	//	svec.push_back(s);
	//}

	//习题8.5一次一个单词
	while (inFile >> s) {
		svec.push_back(s);
	}
	inFile.close();
	if (inFile.eof()) {
		return 4;
	}
	if (inFile.bad()) {
		return 2;
	}
	if (inFile.fail()) {
		return 3;
	}
}

int main() {
	cout << "测试下" << endl;
	vector<string> svec;
	string fileName, s;
	cout << "Enter filename: ";
	cin >> fileName;
	switch (fileToVector(fileName,svec))
	{
		case 1:
			cout << "error: can not open file: " << fileName << endl;
			return -1;
		case 2:
			cout << "error: system failure." << endl;
			return -1;
		case 3:
			cout << "error: read failure." << endl;
			return -1;
	}

	cout << "向量里面的内容：" << endl;
	for (vector<string>::iterator iter = svec.begin();iter != svec.end();++iter)
		cout << *iter << endl;
	return 0;
}

练习8.6-8.7

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

using namespace std;

class Sales_data {
public:
	Sales_data() {}
	Sales_data(std::string bN, unsigned sold, double reven) :bookNo(bN), units_sold(sold), revenue(reven) {}
	std::string isbn() const { return this->bookNo; }
	Sales_data& combine(const Sales_data &rhs) {
		units_sold += rhs.units_sold;
		revenue += rhs.revenue;
		return *this;
	}
	double avg_price() const {
		if (units_sold) {
			return revenue / units_sold;
		}
		else return 0;
	}
	Sales_data add(const Sales_data &lhs, const Sales_data &rhs) {
		Sales_data sum = lhs;
		sum.combine(rhs);
		return sum;
	}
public:
	std::string bookNo; //书号
	unsigned units_sold;
	double revenue;
};

istream &read(istream &is, Sales_data &item) {
	double price = 0;
	is >> item.bookNo >> item.units_sold >> price;
	item.revenue = item.units_sold * price;
	return is;
}

ostream &print(ostream &os, const Sales_data &item) {
	os << item.isbn() << " " << item.units_sold << " " << item.revenue << " " << item.avg_price()<<"
";
	return os;
}


int main(int argc, char **argv)
{
	ifstream input(argv[1]);
	ofstream output(argv[2]);

	Sales_data total;

	if (read(input, total))
	{
		Sales_data trans;

		while (read(input, trans))
		{
			if (total.isbn() == trans.isbn())
			{
				total.combine(trans);
			}
			else
			{
				print(output, total);
				cout << endl;
				total = trans;
			}
		}
		print(output, total);
		cout << endl;
		return 0;
	}
	else
	{
		cerr << "No data?!" << std::endl;
		return -1;  // indicate failure
	}
}

练习8.8

ofstream output(argv[2],ofstream::app);

练习8.9

#include<iostream>
#include<string>
#include<fstream>
#include<sstream>
#include<vector>
using namespace std;

istream &iofunc(istream &is) {
	string s;
	while (is >> s) {
		cout << s << endl;
	}
	is.clear();
	return is;
}

int main() {
	string sss;
	cin >> sss;
	istringstream iss(sss);
	iofunc(iss);
	system("pause");
	return 0;
}

练习8.10

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

using namespace std;

int main() {
	string infile = "test.txt";
	vector<string> svec;
	ifstream in(infile);

	if (in) {
		string buf;
		while (getline(in, buf)) {
			svec.push_back(buf);
		}
	}
	else {
		cerr << "can not open the file:" << infile << endl;
	}
	for (auto s : svec) {
		istringstream iss(s);
		string word;
		while (iss >> word) {
			cout << word << endl;
		}
	}

	system("pause");
	return 0;
}

练习8.11

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

using namespace std;

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

int main() {
	string line, word;
	vector<PersonInfo> people;
	istringstream record;

	while (getline(cin, line)) {
		record.str(line);
		PersonInfo info;
		record >> info.name;
		while (record >> word) {
			info.phones.push_back(word);
		}
		record.clear();
		people.push_back(info);
	}

	for (const auto &entry : people) {
		cout << entry.name << " ";
		for (const auto &ph : entry.phones) {
			cout << ph << " ";
		}
		cout << endl;
	}

	return 0;
}

练习8.12
vector和string在定义后自动初始化。

练习8.13

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

using namespace std;

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

int main() {
	cout << "Please input the fileName:" << endl;
	string infile;
	cin >> infile;
	ifstream in(infile);
	
	if (!in) {
		cerr << "can not open the file: " << infile << endl;
		return 0;
	}

	string line, word;
	vector<PersonInfo> people;
	istringstream record;

	while (getline(in, line)) {
		record.str(line);
		PersonInfo info;
		record >> info.name;
		while (record >> word) {
			info.phones.push_back(word);
		}
		record.clear();
		people.push_back(info);
	}

	for (const auto &entry : people) {
		cout << entry.name << " ";
		for (const auto &ph : entry.phones) {
			cout << ph << " ";
		}
		cout << endl;
	}
	system("pause");
	return 0;
}

练习8.14
无需修改所以用const，另外引用传值更快。