C++程序设计原理与实践 习题答案 第二十三章 第23章习题答案

C++程序设计原理与实践 习题答案 第二十三章 第23章习题答案

第二十三章：文本处理 习题答案

• 本章习题所用到的头文件和实现
• • Text.h
  • Text.cpp
• 23.1 and 23.2
• 23.3 and 23.4
• 23.5
• 23.6
• 23.8
• 23.9
• 23.10
• 23.12
• 23.13
• 23.14

本章习题所用到的头文件和实现 Text.h

#include 
#include 
#include 

Text.cpp

#include "23_Text.h"

Mail_file::Mail_file(const string& fname)
	:name{ fname }
{
	ifstream ifs{ fname };
	if (!ifs)
	{
		cerr << "no " << fname << 'n';
		exit(1);		//终止程序
	}

	for (string s; getline(ifs, s);)	//创建文本行的 vector
		lines.push_back(s);

	auto first = lines.begin();			//创建 Message 的 vector
	for (auto p = lines.begin(); p != lines.end(); ++p)
	{
		if (*p == Mail_delimeter)	//标识邮件结束
		{
			if (first != p)	//处理出现多行 ---- 的情况
				m.push_back(Message{ first,p });
			first = p + 1;		// ---- 不是邮件的一部分
		}
	}
}



//-------------------------------------------------------------------------------
static int is_prefix(const string& s, const string& p)
{
	//p 是 s 的第一部分？
	int n = p.size();
	if (string(s, 0, n) == p)
		return n;
	else
		return 0;
}

//bool find_from_addr(const Message* pm, string& s)
//{
//	for (const auto& x : *pm)
//		if (int n = is_prefix(x, "From: "))
//		{
//			s = string(x, n);
//			return true;
//		}
//	return false;
//}
//
//string find_subject(const Message* pm)
//{
//	for (const auto& x : *pm)
//		if (int n = is_prefix(x, "Subject: "))
//			return string(x, n);
//	return "";
//}


//Exercise 23-3------------------------------------------------------------------
bool find_from_addr(const Message* pm, string& s)
{
	regex pat{ R"(^From:s?(.+)$)" };
	for (const auto& x : *pm)
	{
		smatch matches;
		if (regex_match(x, matches, pat))
		{
			s = matches[1];
			return true;
		}
	}
	return false;
}

string find_subject(const Message* pm)
{
	regex pat{ R"(^Subject:s?(.+)$)" };
	for (const auto& x : *pm)
	{
		smatch matches;
		if (regex_match(x, matches, pat))
			return matches[1];
	}
	return "";
}
//Exercise 23-3 End------------------------------------------------------------------

void print_mail(ostream& os, const Message* pm)
{
	for (const auto& x : *pm)
		os << x << 'n';
}

23.1 and 23.2

#include "23_Text.h"

int main()
{
	cout << "Enter an email file to process:n";
	string fname;
	cin >> fname;
	Mail_file mfile{ fname };		//从一个文件读取数据初始化 mfile

	//将来自每个发件人的邮件收集在一起，保存在一个 multimap 中
	multimap sender;
	//用于保存主题的 multimap
	multimap subject;
	for(const auto& m : mfile)
	{
		string s;
		if (find_from_addr(&m, s))
			sender.insert(make_pair(s, &m));
		//Exercise 23_2
		if ((s = find_subject(&m)).size() != 0)	//如果有找到主题
			subject.insert(make_pair(s, &m));
	}
	//现在遍历 multimap，提取 John Doe 的邮件的主题
	auto pp = sender.equal_range("John Doe ");
	for (auto p = pp.first; p != pp.second; ++p)
		cout << find_subject(p->second) << 'n';

	cin.ignore();	//先把之前输入的最后换行符给去掉
	string subj;	//用于接收主题
	getline(cin, subj);

	auto pp2 = subject.equal_range(subj);
	for(auto p = pp2.first; p != pp2.second; ++p)
	{
		print_mail(cout, p->second);
		cout << Mail_delimeter << 'n';
	}

	return 0;
}

23.3 and 23.4

#include "23_Text.h"


int main()
{
	cout << "Enter an email file to process:n";
	string fname;
	cin >> fname;
	Mail_file mfile{ fname };		//从一个文件读取数据初始化 mfile

	//将来自每个发件人的邮件收集在一起，保存在一个 multimap 中
	multimap sender;

	for (const auto& m : mfile)
	{
		string s;
		if (find_from_addr(&m, s))
			sender.insert(make_pair(s, &m));
	}
	//现在遍历 multimap，提取 John Doe 的邮件的主题
	auto pp = sender.equal_range("John Doe ");
	for (auto p = pp.first; p != pp.second; ++p)
		cout << find_subject(p->second) << 'n';

	//指定发件人
	cout << "Enter sender: ";
	cin.ignore();	//先把之前输入的最后换行符给去掉
	string sdr;
	getline(cin, sdr);
	auto pp2 = sender.equal_range(sdr);
	for (auto p = pp2.first; p != pp2.second; ++p)
		cout << find_subject(p->second) << 'n';

	return 0;
}

23.5

#include "23_Text.h"
#include 
#include 

int main()
{
	cout << "Enter an email file to process:n";
	string fname;
	cin >> fname;
	Mail_file mfile{ fname };		//从一个文件读取数据初始化 mfile

	//将来自每个发件人的邮件收集在一起，保存在一个 multimap 中
	multimap sender;
	for (const auto& m : mfile)
	{
		string s;
		if (find_from_addr(&m, s))
			sender.insert(make_pair(s, &m));
	}

	//将来自每个发件人的邮件收集在一起，保存在一个 unordered_multimap 中
	unordered_multimap sender2;
	for (const auto& m : mfile)
	{
		string s;
		if (find_from_addr(&m, s))
			sender2.insert(make_pair(s, &m));
	}

	//分别测试 multimap 和 unordered_multimap 的输出时间

	auto t1 = chrono::system_clock::now();
	for (const auto& p : sender)
		print_mail(cout, p.second);
	auto t2 = chrono::system_clock::now();
	cout << "Multimap took "
		<< chrono::duration_cast(t2 - t1).count()
		<< " millisecondsn";

	auto t3 = chrono::system_clock::now();
	for (const auto& p : sender2)
		print_mail(cout, p.second);
	auto t4 = chrono::system_clock::now();
	cout << "Unordered_multimap took "
		<< chrono::duration_cast(t4 - t3).count()
		<< " millisecondsn";

	return 0;
}

23.6

#include 

#include "23_Text.h"

//文本文件中的日期格式：月/日/年，比如12/24/2000, 1/1/2022
//月的范围[1,12],暂不检查日和年的合法性

int main()
try
{
	cout << "Enter text file name: ";
	string fname;
	cin >> fname;

	ifstream ifs{ fname };
	if (!ifs)
		throw runtime_error{ "Open file failed" };

	regex pat_date{ R"((d{1,2})/(d{1,2})/(d{4}))" };
	unsigned lineno{ 0 };
	for(string s; getline(ifs,s);)
	{
		++lineno;
		smatch matches;
		if(regex_search(s,matches,pat_date))
		{
			if (4 == matches.size())	//可以不用这个测试
			{
				int month{to(matches[1])};
				if (month >= 1 && month <= 12)
					cout << setw(3) << lineno << ": " << s << 'n';
			}
		}
	}

	return 0;
}
catch(exception& e)
{
	cerr << e.what() << endl;
}

23.8

#include 
#include 
#include 
#include 
#include 

int main()
try {
    std::string pat;
    std::cout << "enter pattern: ";
    std::getline(std::cin, pat);         // read pattern
    std::regex pattern;
    try {
        pattern = pat;                  // this checks pat
        std::cout << "pattern: " << pat << 'n';
    }
    catch (std::regex_error) {
        std::cout << pat << " is not a valid regular expressionn";
        exit(1);
    }

    std::cout << "now enter text file name: ";
    std::string fname;
    std::ifstream ifs{ fname };
    if (!ifs)
        throw std::runtime_error{ "Open file failed" };

	int lineno = 0;
    for (std::string line; std::getline(std::cin, line); ) {
        ++lineno;
        std::smatch matches;
        if (std::regex_search(line, matches, pattern)) {
            std::cout << "line " << lineno << ": " << line << 'n';
        }
    }
}
catch (std::exception& e) {
    std::cerr << "Exception: " << e.what() << 'n';
    return 1;
}
catch (...) {
    std::cerr << "Unknown exceptionn";
    return 2;
}

23.9

#include "../../std_lib_facilities.h"
#include "23_Text.h"

int main()
try {
    //获取文件名
    cout << "Enter table file name: ";
    string fname;
    cin >> fname;

    ifstream in{ fname };     //输入文件
    if (!in) error("no input file");

	string line;    //输入缓冲区

    regex header{ R"(^[w ]+(t[w ]+)*$)" };             //文件头行正则模式
    regex row{ R"(^[w ]+(td+)(td+)(td+)$)" };     //数据行正则模式

    if(getline(in,line))    //检查文件头行
    {
        smatch matches;
        if (!regex_match(line, matches, header))
            error("no header");
    }

    int lineno {0};
    //列合计
    int boys{ 0 };
    int girls{ 0 };

    while(getline(in,line))
    {
        ++lineno;
        smatch matches;
        if (!regex_match(line, matches, row))
            error("bad line: " + to_string(lineno));

        //检查行
        int curr_boy = from_string(matches[1]);
        int curr_girl = from_string(matches[2]);
        int curr_total = from_string(matches[3]);
        if (curr_boy + curr_girl != curr_total)
            error("bad row sum");

        //if(matches[1] == "Alle klasser")      //最后一行
        if (in.eof() || (in >> ws).eof())       //最后一行
        {    cout << "at eofn";
            if (curr_boy != boys)
                error("boys don't add up");
            if (curr_girl != girls)
                error("girls don't add up");
            
            return 0;
        }

        //更新合计
        boys += curr_boy;
        girls += curr_girl;
    }

    error("didn't find total line");
}
catch (std::exception& e) {
    std::cerr << "Exception: " << e.what() << 'n';
    return 1;
}
catch (...) {
    std::cerr << "Unknown exceptionn";
    return 2;
}

23.10

这题感觉代码实现得挺丑陋的。。。

#include 
#include "../../std_lib_facilities.h"
#include "23_Text.h"

//一个年级的男女同学数量和总和
struct Grade_students
{
    int grade;
    int boys;
    int girls;
    int total;    //本年级的所有学生
};

ostream& operator<<(ostream& os, const Grade_students& gs)
{
    os << gs.grade
        << 't' << gs.boys
        << 't' << gs.girls
        << 't' << gs.total;
    return os;
}

int main()
try {
    //获取文件名
    cout << "Enter table file name: ";
    string fname;
    cin >> fname;

    ifstream in{ fname };     //输入文件
    if (!in) error("no input file");

    string line;    //输入缓冲区
    

    regex header{ R"(^([w ]+)(t[w ]+)*$)" };             //文件头行正则模式
    regex row{ R"(^([w ]+)(td+)(td+)(td+)$)" };     //数据行正则模式
    regex colum_1{ R"((d+)w+)" };              //第一列带数字的正则模式

    if (getline(in, line))    //检查文件头行
    {
        smatch matches;
        if (!regex_match(line, matches, header))
            error("no header");
    }
    string tbl_hdr{ line };                //表头
    constexpr int REST_grd { -1 };         //剩余没有年级的为一组
    const string REST_str{ "REST"};   //剩余没有年级的为一组
    Grade_students REST_students;

    map students;     //统计学生，合并同年级的班级学生

	int lineno{ 0 };
    //列合计
    int boys{ 0 };
    int girls{ 0 };


    while (getline(in, line))
    {
        ++lineno;
        smatch matches;
        if (!regex_match(line, matches, row))
            cerr << "bad line: " << lineno << 'n';

        if (in.eof()) cout << "at eofn";

        //检查行
        int curr_boy = from_string(matches[2]);
        int curr_girl = from_string(matches[3]);
        int curr_total = from_string(matches[4]);
        if (curr_boy + curr_girl != curr_total)
            error("bad row sum");

        //添加/合并进set
        smatch matches2;
        string str_col_1 = matches[1];
        if(regex_match(str_col_1, matches2, colum_1))   //如果第一列匹配
        {
            int grd = from_string(matches[1]);
            auto p = students.find(grd);
            if (p == students.end())
                students[grd] = Grade_students{ grd,curr_boy,curr_girl,curr_total };
            else
            {
                students[grd].boys += curr_boy;
                students[grd].girls += curr_girl;
                students[grd].total += curr_total;
            }
        }
        else if(matches[1] == REST_str)
        {
            REST_students = { REST_grd,curr_boy,curr_girl,curr_total };
        }
        else if (matches[1] == "Alle klasser")    //最后一行
        {
            if (curr_boy != boys)
                error("boys don't add up");
            if (curr_girl != girls)
                error("girls don't add up");
            if (!(in >> ws).eof())
                error("characters after total line");
            //输出新的表格到文件中
            string ofname;
            cout << "Enter ouput file name: ";
            cin >> ofname;
            ofstream out{ ofname };     //输入文件
            if (!out) error("can't open output file");
            out << tbl_hdr << 'n';
            for (const auto& record : students)
                out << record.second << 'n';
            out << REST_str
                << 't' << REST_students.boys
                << 't' << REST_students.girls
                << 't' << REST_students.total
                << 'n';
            out << matches[1]
                << matches[2]
                << matches[3]
                << matches[4]
                << 'n';
            return 0;
        }

        //更新合计
        boys += curr_boy;
        girls += curr_girl;
    }

    error("didn't find total line");
}
catch (std::exception& e) {
    std::cerr << "Exception: " << e.what() << 'n';
    return 1;
}
catch (...) {
    std::cerr << "Unknown exceptionn";
    return 2;
}

23.12

#include "23_Text.h"

//文本文件中的日期格式：月/日/年，比如12/24/2000, 1/1/2022
//月的范围[1,12],暂不检查日和年的合法性
//ISO标准 yyyy-mm-dd

string replace_to_iso_date(const string& line)
{
	//用三次regex_replace，效率有些低

	//第一次先换到正确位置
	regex pat_date1 { R"((d{1,2})/(d{1,2})/(d{4}))" };
	string fmt1{ "$3-$1-$2" };
	string s1 = regex_replace(line, pat_date1, fmt1);

	//第二次给月份补零（如果月份不是2位数字的话）
	regex pat_date2{ R"((d{4})-(d)-(d{1,2}))" };
	string fmt2{ "$1-0$2-$3" };
	string s2 = regex_replace(s1, pat_date2, fmt2);

	//第二次给日期补零（如果日期不是2位数字的话）
	//注意最后的日期这边，有三种情况，一、1个 d 配上其他字符，二、1个 d 后面没有字符，
	//三、2个 d。我们匹配一和二两种情况
	regex pat_date3{ R"((d{4})-(d{2})-(d)(D|$))" };		
	string fmt3{ "$1-$2-0$3$4" };
	return regex_replace(s2, pat_date3, fmt3);
}

int main()
try
{
	cout << "Enter input file name: ";
	string ifname;
	cin >> ifname;

	cout << "Enter output file name: ";
	string ofname;
	cin >> ofname;

	ifstream ifs{ ifname };
	if (!ifs)
		throw runtime_error{ "Open input file failed" };
	ofstream ofs{ ofname };
	if (!ofs)
		throw runtime_error{ "Open output file failed" };

	regex pat_date{ R"(^(.*?)(d{1,2})/(d{1,2})/(d{4}))" };		//法2，其中.*?是惰性匹配，而.*是贪婪匹配
	//输出
	for (string line; getline(ifs, line);)
	{
		//法1
		ofs << replace_to_iso_date(line) << 'n';	
		//法2
		//smatch matches;
		//if (regex_search(line, matches, pat_date))
		//{
		//	do {
		//		int month{ to(matches[2]) };
		//		
		//			//接下来转换到ISO日历，并按序补成两位数的月份和日期
		//		ofs << matches[1] << matches[4] << '-';
		//		if (month < 10)
		//			ofs << '0';
		//		ofs << month << '-';
		//		if (matches[3].str().size() == 1)
		//			ofs << '0';
		//		ofs << matches[3];
		//		line = matches.suffix().str();		//格式化日期之后余下的字符串需要再次进行模式匹配
		//	} while (regex_search(line, matches, pat_date));
		//}
		//ofs << line << 'n';
	}

	return 0;
}
catch (exception& e)
{
	cerr << e.what() << endl;
}

23.13

#include "../../std_lib_facilities.h"

int main()
try
{
	string s{ "n" };
	regex pat{ R"(.)" };
	smatch matches;
	if (regex_match(s, matches, pat))
		cout << ". can match '\n'n";
	else
		cout << ". can match '\n'n";

	return 0;
}
catch(exception& e)
{
	cerr << e.what() << endl;
	return 1;
}

23.14

#include 
#include 
#include 
#include 
#include 

using namespace std;

int main()
try {
    std::string fname;
    cout << "Enter input file name: ";
    cin >> fname;
    std::ifstream ifs{ fname };
    if (!ifs) {
        std::cerr << "Could not read from file " << fname << 'n';
        exit(1);
    }
    cin>>ws;   //把空白符都除掉，包括换行符

    std::string file_str;
    for (std::string s; std::getline(ifs, s); )
        file_str += s + 'n';

    while (true) {
        std::regex pattern;
        std::cout << "enter pattern to test:n";
        std::string pat;
        std::getline(std::cin, pat);

        try {
            pattern = pat;          // test pattern
            std::cout << "pattern: " << pat << 'n';
        }
        catch (std::regex_error) {
            std::cerr << pat << " is not a valid regular expressionn";
            exit(1);
        }

        std::smatch matches;
        if (std::regex_search(file_str, matches, pattern)) {
            std::cout << "Match!n";
            for (const auto& m : matches)
                std::cout << 't' << m << 'n';
        }
        else {
            std::cout << "No match..n";
        }
    }
}
catch (std::exception& e) {
    std::cerr << "Exception: " << e.what() << 'n';
    return 1;
}
catch (...) {
    std::cerr << "Unknown exceptionn";
    return 2;
}