c++primer第五版第十七章练习

16-04-20 来源：[db:作者]

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17.1、17.2

#include 
#include 
#include 
#include 
int main()
{
	using namespace std;
	tuple ti{ 10,20,30 };
	cout << get<0>(ti) << " " << get<1>(ti) << " " << get<2>(ti) << endl;

	tuple, pair> top;
	system("pause");
	return 0;
}

17.3

#pragma once
#include 
#include 
#include 
#include 
#include
#include 
#include 
class TextQuery
{
public:
	typedef std::vector::size_type _type;
	typedef std::tuple>, std::shared_ptr<>>> QueryResult;
private:
	std::shared_ptr<>> file;
	std::map>> ms;

public:
	TextQuery(std::ifstream &ifile);
	QueryResult query(const std::string &s)const;
	QueryResult query_tuple(const std::string &s);
};

#include "textquery.h"
#include 
#include 
#include 
TextQuery::TextQuery(std::ifstream &ifile) :file(new std::vector)
{
	std::string line;
	while (std::getline(ifile, line))
	{
		file->push_back(line);
		
		std::stringstream sstr(line);
		std::string word;

		while (sstr >> word)
		{
			//std::shared_ptr<>> &sptr = ms[word];
			auto &sptr = ms[word];
			if (!sptr)
				sptr.reset(new std::set<_type>);
			sptr->insert(file->size() - 1);
		}
	}
}
TextQuery::QueryResult TextQuery::query(const std::string &s)const
{
	static std::shared_ptr> nodata(new std::set<_type>);

	auto iter = ms.find(s);
	if (iter == ms.end())
		return QueryResult(s, nodata, file);
	else
		return QueryResult(s, iter->second, file);
}

TextQuery::QueryResult TextQuery::query_tuple(const std::string &s)
{
	static std::shared_ptr> nodata(new std::set<_type>);
	auto iter = ms.find(s);
	if (iter == ms.end())
		return QueryResult(s, nodata, file);
	else
		return QueryResult(s, iter->second, file);
}

#include
#include
#include "textquery.h"

std::ostream &operator<<(std::ostream &os, const TextQuery::QueryResult &q)
{
	os << std::get<0>(q) << "\n";
	for (auto &x : *std::get<1>(q))
		os << x << " ";
	os << "\n";
	for (auto &x : *std::get<2>(q))
		os << x << " ";
	return os;
}

int main(int agrc,char **argv)
{
	using namespace std;
	ifstream ifile(argv[1]);
	if (!ifile)
	{
		cout << "open file error!";
		exit(1);
	}
	TextQuery b(ifile);
	cout< 
原来的方法比较好
tuple用于快速生成，但却难以重构，可用于快速的测试

17.4、17.5、17.6

#pragma once
#include 
#include 
class Sales_data
{
	friend Sales_data operator+(const Sales_data& lhs, const Sales_data& rhs);
	friend std::ostream &operator << (std::ostream& os, const Sales_data& s);
	friend std::istream &operator >> (std::istream& is, Sales_data& s);
	friend Sales_data add(const Sales_data&, const Sales_data&);
	friend std::ostream &print(std::ostream&, const Sales_data&);
	friend std::istream &read(std::istream&, Sales_data&);
public:
	Sales_data() = default;
	Sales_data(const std::string &s) : bookNo(s) { }
	Sales_data(const std::string &s, unsigned n, double p) :bookNo(s), units_sold(n), revenue(p*n){}
	Sales_data(const Sales_data &s) :bookNo(s.bookNo), units_sold(s.units_sold), revenue(s.revenue){}
	Sales_data(Sales_data&& s) :bookNo(s.bookNo), units_sold(s.units_sold), revenue(s.revenue){}
	~Sales_data() {}
	Sales_data(std::istream &);
	std::string isbn() const { return bookNo; }
	Sales_data& combine(const Sales_data&);
	Sales_data& operator  =(const Sales_data& rhs);
	Sales_data& operator  =(const std::string&  rhs);
	Sales_data& operator +=(const Sales_data& rhs);
	explicit operator std::string() const { return bookNo; }
	explicit operator double() const { return revenue; }
	double avg_price() const;
private:
	std::string bookNo;
	unsigned units_sold = 0;
	double revenue = 0.0;
};
inline Sales_data operator+(const Sales_data& lhs, const Sales_data& rhs)
{
	Sales_data sum = lhs;
	sum += rhs;

	return sum;
}
std::ostream &operator << (std::ostream& os, const Sales_data& item);
std::istream &operator >> (std::istream& is, Sales_data& s);
Sales_data add(const Sales_data&, const Sales_data&);
std::ostream &print(std::ostream&, const Sales_data&);
std::istream &read(std::istream&, Sales_data&);

#include 
#include "Sales_data.h"
using std::istream; using std::ostream;
Sales_data::Sales_data(std::istream &is)
{
	read(is, *this);
}
double Sales_data::avg_price() const {
	if (units_sold)
		return revenue / units_sold;
	else
		return 0;
}
Sales_data &Sales_data::combine(const Sales_data &rhs)
{
	units_sold += rhs.units_sold;
	revenue += rhs.revenue;
	return *this;
}
Sales_data &Sales_data::operator =(const Sales_data &rhs)
{
	this->bookNo = rhs.bookNo;
	this->revenue = rhs.revenue;
	this->units_sold = rhs.units_sold;
	return *this;
}
Sales_data &Sales_data::operator =(const std::string &rhs)
{
	*this = Sales_data(rhs);
	return *this;
}
Sales_data &Sales_data::operator +=(const Sales_data &rhs)
{
	this->revenue += rhs.revenue;
	this->units_sold += rhs.units_sold;
	return *this;
}
Sales_data add(const Sales_data &lhs, const Sales_data &rhs)
{
	Sales_data sum = lhs;
	sum.combine(rhs);
	return sum;
}
istream &read(istream &is, Sales_data &item)
{
	double price = 0;
	is >> item.bookNo >> item.units_sold >> price;
	item.revenue = price * item.units_sold;
	return is;
}
ostream &print(ostream &os, const Sales_data &item)
{
	os << item.isbn() << " " << item.units_sold << " "<< item.revenue << " " << item.avg_price();
	return os;
}
std::ostream &operator <<(std::ostream &os, const Sales_data &item)
{
	os << item.isbn() << " " << item.units_sold << " "<< item.revenue << " " << item.avg_price();
	return os;
}
std::istream &operator >>(std::istream &is, Sales_data &s)
{
	double price;
	is >> s.bookNo >> s.units_sold >> price;
	if (is)
		s.revenue = s.units_sold * price;
	else
		s = Sales_data();

	return is;
}

#include 
#include 
#include 
#include 
#include 	//equal_range
#include 
#include 		//accumulate
#include 
#include "Sales_data.h"
typedef std::tuple<>::size_type, std::vector::const_iterator, std::vector::const_iterator> matches;
typedef std::pair<>::size_type, std::pair<>::const_iterator, std::vector::const_iterator>>matches_pair;
inline bool compareIsbn(const Sales_data &ls, const Sales_data &rs)
{
	return ls.isbn() < rs.isbn();
}

std::vector findbook(const std::vector<>> &f, const std::string &book)//17.4
{
	std::vector ret;
	for (auto it = f.cbegin(); it != f.cend(); ++it)
	{
		auto found = equal_range(it->cbegin(), it->cend(), book, compareIsbn);
		if (found.first != found.second)
			ret.push_back(make_tuple(it - f.cbegin(), found.first, found.second));
	}
	return ret;
}
std::vector findbook_pair(const std::vector<>> &f, const std::string &book)//17.5
{
	std::vector ret;
	for (auto it = f.cbegin(); it != f.cend(); ++it)
	{
		auto found = equal_range(it->cbegin(), it->cend(), book, compareIsbn);
		if (found.first != found.second)
			ret.push_back(make_pair(it - f.cbegin(), make_pair(found.first, found.second)));
	}
	return ret;
}
struct matches_struct//17.6
{
	std::vector::size_type st;
	std::vector::const_iterator first;
	std::vector::const_iterator second;
	matches_struct(std::vector::size_type s, std::vector::const_iterator fi, std::vector::const_iterator se) :st(s), first(fi), second(se) {}
};
std::vector findbook_struct(const std::vector<>> &f, const std::string &book)
{
	std::vector ret;
	for (auto it = f.cbegin(); it != f.cend(); ++it)
	{
		auto found = equal_range(it->cbegin(), it->cend(), book, compareIsbn);
		if (found.first != found.second)
			ret.push_back(matches_struct(it - f.cbegin(), found.first, found.second));
	}
	return ret;
}
void reportRestults(std::istream &is, std::ostream &os, const std::vector<>> &f)
{
	std::string s;
	while (is >> s)
	{
		auto tran = findbook(f, s);
		if (tran.empty())
		{
			std::cout << s << " not found in any stores" << std::endl;
			continue;
		}
		for (const auto &x : tran)
			os << "store " << std::get<0>(x) << " sales: " << std::accumulate(std::get<1>(x), std::get<2>(x), Sales_data(s)) << std::endl;
	}
}
std::vector *write_sales(std::fstream &f)
{
	Sales_data temp;
	auto ptr = new std::vector;
	while (read(f, temp))
	{
		ptr->push_back(temp);
	}
	return ptr;
}
int main(int argc,char **argv)
{
	using namespace std;
	fstream f1(argv[1]), f2(argv[2]), f3(argv[3]);
	if (!f1&&!f2&&!f3)
	{
		cerr << "error!";
		exit(1);
	}
	std::vector<>> file;
	file.push_back(*write_sales(f1));
	file.push_back(*write_sales(f2));
	file.push_back(*write_sales(f3));

	reportRestults(cin, cout, file);
	system("pause");
	return 0;
}

17.7

更倾向于tuple，相对于其他版本，它更方便

17.8

创建的是使用Sales_data默认构造函数创建的对象

这样的结果就是书名为空，其他数据为0

17.9

a、00000000 00000000 00000000 00000000 00000000 00000000 00000000 00100000

b、00000000 00001111 01101001 10110101

c、视输入的内容而定，但是输入的字符非0或1那么就会抛出invalid_argument异常

17.10

#include 
#include 

int main()
{
	using namespace std;
	int v[] = { 1,2,3,5,8,13,31 };
	bitset<32> bit1;
	for (auto x : v)
		bit1.set(x);
	bitset<32> bit2;
	for (size_t i = 0; i < bit1.size(); ++i)
		bit2[i] = bit1[i];
	cout << bit1 << endl << bit2;
	system("pause");
	return 0;
}

17.11、17.12、17.13

#pragma once
#include 
#include 
#include 

template
class Bit							//17.11
{
	std::bitset bit;
public:
	Bit() = default;
	Bit(std::string &s) :bit(s) {}

	void updata(size_t n, bool b)	//17.12
	{
		bit.set(n, b);
	}

	template			//17.13
	friend size_t text(const Bit &lb, const Bit &rb);

	template
	friend std::ostream &operator<<(std::ostream &os, const Bit &b);
};

template
size_t text(const Bit &lb, const Bit &rb)
{
	auto temp = lb.bit^rb.bit;	//得出答错的题目
	temp.flip();				//翻转所有
	return temp.count();		//返回答对的题目
}

template
std::ostream &operator<<(std::ostream &os, const Bit &b)
{
	os << b.bit;
	return os;
}

17.14

#include 
#include 
#include 
int main()
{
	using namespace std;
	try {
		regex reg("[^cei");
	}
	catch (regex_error e){
		cout << e.what() << "\ncode: " << e.code() << endl;
	}
	

	system("pause");
	return 0;
}

17.15、17.16

#include 
#include 
#include 

int main()
{
	using namespace std;
	regex reg("[[:alpha:]]*[^c]ei[[:alpha:]]*",regex::icase);//17.15
	string str;
	smatch m;
	while (cin >> str&&str!="q")		
	{
		if (regex_search(str, m, reg))
			cout << str << " is ok" << endl;
		else
			cout << str << " is not ok" << endl;
	}

	reg = "[^c]ei";//17.16 好像...并没有什么变化
	while (cin >> str&&str != "q")
	{
		if (regex_search(str, m, reg))
			cout << str << " is ok" << endl;
		else
			cout << str << " not is ok" << endl;
	}

	system("pause");
	return 0;
}

17.17、17.18

#include 
#include 
#include 
#include 
#include 
int main(int argc, char **argv)
{
	using namespace std;
	ifstream file(argv[1]);
	if (!file)
	{
		cerr << "open file error!";
		exit(1);
	}
	string p("[^c]ei");
	p = "[[:alpha:]]*" + p + "[[:alpha:]]*";
	regex reg(p, regex::icase);
	string temp, str;
	while (getline(file, temp))
		str = str + temp + "\n";
	vector vec{ "albeit","beige","feint","heir","reign","their",
		"counterfeit","foreign","inveigh","rein","veil","deign",
		"forfeit","inveigle","seize","veineiderdown","freight",
		"leisure","skein","weigheight","heifer","neigh","sleigh",
		"weighteither","height","neighbour","sleight","weirfeign",
		"heinous neither surfeit weird" };
	for (sregex_iterator it(str.begin(), str.end(), reg), end_it; it != end_it; ++it)
	{
		if (find(vec.begin(), vec.end(), it->str()) != vec.end())//17.8
			continue;
		cout << it->str();
		system("pause");
		auto pos = it->prefix().length();
		cout << it->prefix().str().substr(pos > 40 ? pos - 40 : 0) << "[> " << it->str() << "<]" << it->suffix().str().substr(0, 40) << endl;
	}

	system("pause");
	return 0;
}

17.19

m4和m6都是分隔符，两者必须是相同的字符，如果一方不匹配或两者不相同，那么就为true

17.20

#include 
#include 
#include 
bool valid(const std::smatch &m);
int main()
{
	using namespace std;

	string phone = "(\\()?(\\d{3})(\\))?([-. ])?(\\d{3})([-. ])?(\\d{4})";
	regex reg;
	try {
		reg.assign(phone);
	}
	catch (regex_error e) {
		cout << e.what() << "\ncode: " << e.code();
	}
	smatch m;
	string s;
	while (getline(cin, s)&&s!="q")
	{
		for (sregex_iterator it(s.begin(), s.end(), reg), end_it; it != end_it; ++it) 
		{
			if (valid(*it))
				cout << "valid: " << it->str() << endl;
			else
				cout << "not valid: " << it->str() << endl;
		}
	}
	system("pause");
	return 0;

}

bool valid(const std::smatch &m)
{
	if (m[1].matched)//如果存在"("左括号
		// ")"右括号必须存在，和区号分隔符不存在，或区号分隔符为空格
		return m[3].matched && (m[4].matched == 0 || m[4].str() == " ");
	else			//如果不存在"("左括号
		// ")"右括号必须不存在，和区号分隔符与号码分隔符必须相同
		return !m[3].matched&&m[4].str() == m[6].str();
}

17.21

#include 
#include 
#include 
#include 
#include 
#include 

struct PersonInfo {
	std::string name;
	std::vector phones;
};
bool valid(const std::smatch &m);
bool read_record(std::istream &is, std::vector &people);
void format_record(std::ostream &os, const std::vector &people);

int main()
{
	using namespace std;
	vector people;
	string filename;
	cout << "enter input file name:";
	cin >> filename;
	ifstream fin(filename);
	if (read_record(fin, people))
	{
		cout << "enter output file name:";
		string outname;
		cin >> outname;
		ofstream fout(outname, ofstream::trunc); //覆盖文件:trunc
		format_record(fout, people);
	}
	else
		cout << "open file error:" << filename << endl;

	system("pause");
	return 0;
}

bool valid(const std::smatch &m)
{
	if (m[1].matched)
		return m[3].matched && (m[4].matched == 0 || m[4] == " ");
	else
		return !m[3].matched&&m[4].str() == m[6].str();
}
bool read_record(std::istream &is, std::vector &people)
{
	if (is)
	{
		std::string line, word;
		while (getline(is, line))		//读取一行到line
		{
			PersonInfo info;
			std::istringstream record(line);	//关联流到line，把record绑定到要读取的行line
			record >> info.name;		//把流中第一个字符串输入到name，这一行的第一个，也就是名字
			while (record >> word)		
				info.phones.push_back(word);//把名字后面的电话号码保存
			people.push_back(info);		//添加一个联系人
		}
		return true;
	}
	else
		return false;
}
void format_record(std::ostream &os, const std::vector &people)
{
	std::string phone = "(\\()?(\\d{3})(\\))?([-. ])?(\\d{3})([-. ]?)(\\d{4})";
	std::regex reg;
	try {
		reg.assign(phone);
	}
	catch (std::regex_error e)
	{
		std::cout << e.what() << "\ncode: " << e.code() << std::endl;
	}
	std::smatch m;
	for (const auto &x : people)
	{
		std::ostringstream formatted, badNums;
		for (const auto &n : x.phones)
		{
			for (std::sregex_iterator it(n.begin(), n.end(), reg), end_it; it != end_it; ++it)
			{
				if (!valid(*it))
					badNums << " " << n;	//将数据放入流，暂时保存
				else
					formatted << " " << n;
			}
		}
		if (badNums.str().empty())
			os << x.name << " " << formatted.str() << std::endl;	//将流中的数据以string的形式放入os流中
		else
			std::cerr << "file error: " << x.name << " invalid number " << badNums.str() << std::endl;
	}
}

17.22

#include 
#include 
#include 
bool valid(const std::smatch &m);
int main()
{
	using namespace std;

	string phone = "(\\()?(\\d{3})(\\))?([[:blank:]]*)?(\\d{3})([[:blank:]]*)?(\\d{4})";	//（[[:blank:]]）匹配0-哪个空格或制表符
	regex reg;
	try {
		reg.assign(phone);
	}
	catch (regex_error e) {
		cout << e.what() << "\ncode: " << e.code();
	}
	smatch m;
	string s;
	while (getline(cin, s)&&s!="q")
	{
		for (sregex_iterator it(s.begin(), s.end(), reg), end_it; it != end_it; ++it) 
		{
			if (valid(*it))
				cout << "valid: " << it->str() << endl;
			else
				cout << "not valid: " << it->str() << endl;
		}
	}
	system("pause");
	return 0;

}

bool valid(const std::smatch &m)
{
	if (m[1].matched)//如果存在"("左括号
		// ")"右括号必须存在，和区号分隔符不存在，或区号分隔符为空格
		return m[3].matched && (m[4].matched == 0 || m[4].str() == " ");
	else			//如果不存在"("左括号
		// ")"右括号必须不存在，和区号分隔符与号码分隔符必须相同
		return !m[3].matched&&m[4].str() == m[6].str();
}

17.23

#include 
#include 
#include 

int main()
{
	using namespace std;
	string s = "(\\d{5})([-])?(\\d{4})?";
	string num;
	regex reg(s);
	smatch m;
	while (getline(cin, num) && num != "q")
	{
		for (sregex_iterator it(num.begin(), num.end(), reg), end_it; it != end_it; ++it)
		{
			if ((*it)[3].matched)
				cout << it->str();
			else
				cout << it->str(1);
			cout << endl;
		}
	}
	system("pause");
	return 0;
}

17.24

#include 
#include 
#include 

int main()
{
	using namespace std;

	string phone = "(\\()?(\\d{3})(\\))?([[:blank:]]*)?(\\d{3})([[:blank:]]*)?(\\d{4})";
	regex reg;
	try {
		reg.assign(phone);
	}
	catch (regex_error e) {
		cout << e.what() << "\ncode: " << e.code();
	}
	string fmt = "$2.$5.$7";
	smatch m;
	string s;
	while (getline(cin, s) && s != "q")
	{
		cout << regex_replace(s, reg, fmt) << endl;
	}
	system("pause");
	return 0;

}

17.25

#include 
#include 
#include 

int main()
{
	using namespace std;
	string pattern = "(\\()?(\\d{3})(\\))?([-. ])?(\\d{3})([-. ])?(\\d{4})";
	string fmt = "$2.$5.$7";
	regex r(pattern);
	string s;
	while (getline(cin, s))
	{
		smatch result;
		regex_search(s, result, r);
		if (!result.empty())
		{			//prefix输出匹配前的字符  //format(fmt)输出匹配的格式的字符串
			cout << result.prefix() << result.format(fmt) << endl;
		}
		else
		{
			cout << "木有匹配的" << endl;
		}
	}
	system("pause");
	return 0;
}

17.26

#include 
#include 
#include 

int main()
{
	using namespace std;
	string pattern = "(\\()?(\\d{3})(\\))?([-. ])?(\\d{3})([-. ])?(\\d{4})";
	string fmt = "$2.$5.$7";
	regex r(pattern);
	string s;
	while (getline(cin, s))
	{
		smatch result;
		regex_search(s, result, r);
		if (!result.empty())
		{			//prefix输出匹配前的字符  //suffix输出匹配的字符串后面的字符
			cout << result.prefix() << result.suffix()<< endl;
		}
		else
		{
			cout << "木有匹配的" << endl;
		}
	}
	system("pause");
	return 0;
}

17.27

#include 
#include 
#include 

int main()
{
	using namespace std;

	string p = "(\\d{5})(\\d{4})";
	regex reg(p);
	string fmt = "$1-$2";
	smatch m;
	string n;
	while (getline(cin, n) && n != "q")
	{

		cout << regex_replace(n, reg, fmt, regex_constants::match_flag_type::format_no_copy);
	}
	system("pause");
	return 0;
}

17.28、17.29、17.30

#include 
#include 
#include 

unsigned ran()	//17.28
{
	std::default_random_engine e;
	std::uniform_int_distribution u;
	return u(e);
}

unsigned ran(unsigned s)//7.29
{
	std::default_random_engine e(s);
	std::uniform_int_distribution u;
	return u(e);
}

unsigned ran(unsigned s, int f, int l)//17.30
{
	std::default_random_engine e(s);
	std::uniform_int_distribution u(f, l);
	return u(e);
}

int main()
{
	using namespace std;

	unsigned f, l;
	cout << ran() << endl;
	cout << ran(time(0));
	cout << "enrer seed:";
	cin >> f >> l;
	cout << ran(time(0), f, l);
	system("pause");
	return 0;
}

17.31

结果每次都相同。

因为引擎返回相同的随机数序列，所以必须在循环外声明引擎对象，否则每次循环都会创建一个新的引擎（随机数序列不变），而每次都会输出引擎的序列

17.32

resp不在作用域，找不到resp对象

如果在循环里创建resp：

do{

string resp;

}while(...);

在这里，while的前面循环体已经退出，释放所有在循环体定义的对象，所以resp已经不存在

17.33

#include 
#include 
#include 
#include 
#include
#include 
std::map buildmap(std::ifstream &ifile)	//初始化map
{
	std::map temp;
	std::string str, f, s;
	while (getline(ifile, str))
	{
		std::istringstream sst(str);
		sst >> f >> s;
		temp[f] = s;		//把暗文对应的明文设置
	}
	return temp;
}
std::string trans(const std::string &s, std::map &m)//转换
{
	auto temp = m.find(s);
	if (temp != m.end())	//如果是暗文
		return m[s];		//返回暗文对应的明文
	else
		return s;
}
std::string trans_random(const std::string &s, std::map &m)//转换
{
	auto temp = m.find(s);
	if (temp != m.end())	//如果是暗文
		return (m[s]+"!");		//返回暗文对应的明文
	else
		return s;
}
int main(int argc, char **argv)
{
	using namespace std;
	ifstream ifpw(argv[1]), iftxt(argv[2]);
	if (!ifpw&&!iftxt)
	{
		cerr << "open file error!\n";
		exit(1);
	}
	map pw(buildmap(ifpw));	//初始化密码文件
	string temp, f;
	default_random_engine e;
	bernoulli_distribution b;
	bool t;
	while (getline(iftxt, temp))
	{
		istringstream iss(temp);
		while (iss >> f)
		{
			t = b(e);
			if(t)
				cout << trans_random(f, pw) << " ";	//输出f的明文（如果f是暗文）
			else
				cout << trans(f, pw) << " ";	//输出f的明文（如果f是暗文）
		}
		cout << endl;
	}
	system("pause");
	return 0;
}

17.34、17.35、17.36

#include 
#include 

int main()
{
	using namespace std;
	cout << unitbuf;//17.34
	cout << boolalpha << (5 < 4 ? true : false) << noboolalpha << endl;
	cout << showpos << showbase << hex << 1000 << " " << oct << 1000 
		<< " " << dec << 1000 << noshowbase << noshowpos << endl;
	cout << uppercase << 3.14159 << " " << hex << 1000 << dec 
		<< nouppercase << endl;
	cout << setfill('#') << setw(10) << internal << showpos << 1024 
		<< noshowpos << nounitbuf << ends << endl << flush;
	cout << setw(10) << left <="" noskipws;="" while="" (cin="" >>="" ch&&ch="" !="q" )="" cout="" <<="" ch;="" cin="" skipws;="" endl;="" uppercase;="" 17.35="" "default="" format:="" "="" 100="" *="" sqrt(2.0)="" '\n'="" "scientific:="" scientific="" "fixed="" decimal:="" fixed="" "hexidecimal:="" uppercase="" hexfloat="" "use="" defaults:="" defaultfloat="" setfill('="" ');="" 17.36="" left="" setw(20)="" format:"="" setw(25)="" right="" "scientific:"="" decimal:"="" "hexidecimal:"="" defaults:"="" "\n\n";="" system("pause");="" return="" 0;="" }

17.37

#include 
#include 
int main(int argv, char **argc)
{
	using namespace std;
	ifstream ifile(argc[1]);
	if (!ifile)
	{
		cout << "open file error!";
		exit(1);
	}
	char ar[100];
	do {
		ifile.getline(ar, 10);//当行超出10个字符时停止
		cout << ar << ' ';
	} while (ifile);	
	ifile.close();
	system("pause");
	return 0;
}

17.38

#include 
#include 
int main(int argv, char **argc)
{
	using namespace std;
	ifstream ifile(argc[1]);
	if (!ifile)
	{
		cout << "open file error!";
		exit(1);
	}
	char ar[100];
	do {
		ifile.getline(ar, 100,' ');
		cout << ar << ' ';
	} while (ifile);
	ifile.close();
	system("pause");
	return 0;
}

17.39

#include 
#include 
#include 
int main(int argc, char **argv)
{
	using namespace std;

	fstream iofile(argv[1],fstream::ate|fstream::in|fstream::out);//以只读、只写和文件指针跳到文件尾的方式打开
	if (!iofile)
	{
		cerr << "open file error!";
		exit(1);
	}

	auto end_mark = iofile.tellg();//返回当前文件指针的位置
	iofile.seekg(0, fstream::beg);//文件指针跳到文件头，偏移0
	size_t cnt = 0;
	string line;
	while (iofile&&iofile.tellg() != end_mark&&getline(iofile,line))//确定当前文件io流可用与文件当前位置不是原文件尾
	{
		cnt += line.size() + 1;//增加当前行的长度，+1表示换行符也算
		auto mark = iofile.tellg();//保存当前文件指针
		iofile.seekp(0, fstream::end);//文件指针跳到文件尾
		iofile << cnt;//写入长度
		if (mark != end_mark)//确定原位置不是原文件尾
			iofile << " ";
		iofile.seekg(mark);
	}
	iofile.seekp(0, fstream::end);
	iofile << "\n";
	iofile.close();

	system("pause");
	return 0;
}

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