C++Primer第五版 习题答案 第八章 IO库（The IO Library）

8.1

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

8.2

#include <iostream>
#include <string>

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

int main()
{
    iofunction(std::cin);

    std::string s1;
    while(std::cin >> s1)
        std::cout << s1 << std::endl;

    return 0;
}

8.3

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

8.4

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

using namespace std;

int main()
{
    ifstream ifs("data");
    vector<string> v1;
    string buf;

    if(ifs)
    {
        while(getline(ifs,buf))
        {
            v1.push_back(buf);
        }
    }


    for(const auto &s : v1)
        cout << s << endl;

    return 0;
}

8.5

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

using namespace std;

int main()
{
    ifstream ifs("data");
    vector<char> v1;
    char buf;

    if(ifs)
    {
        while(ifs >> buf)
        {
            v1.push_back(buf);
        }
    }


    for(const auto &c : v1)
        cout << c << endl;

    return 0;
}

8.6

本题使用习题7.26的代码，和题目中略有不同，并不影响。

#include <iostream>
#include <string>
#include <fstream>
#include "../ch07_Classes/Sales_data_ex26.h"

int main(int argc, char **argv)
{
    std::ifstream ifs(argv[1]);

    if(!ifs) return 1;

    Sales_data total(ifs);

    if (!total.isbn().empty())
    {
        Sales_data trans;

        while (read(ifs, trans))
        {
            if (total.isbn() == trans.isbn())
            {
                total.combine(trans);
            }
            else
            {
                print(std::cout, total);
                std::cout << std::endl;
                total = trans;
            }
        }
        print(std::cout, total);
        std::cout << std::endl;

        return 0;
    }
    else
    {
        std::cerr << "No data?!" << std::endl;
        return -1;  // indicate failure
    }
}

8.7

#include <iostream>
#include <string>
#include <fstream>
#include "../ch07_Classes/Sales_data_ex26.h"

int main(int argc, char **argv)
{
    std::ifstream ifs(argv[1]);
    std::ofstream ofs(argv[2]);

    if(!ifs) return 1;

    Sales_data total(ifs);

    if (!total.isbn().empty())
    {
        Sales_data trans;

        while (read(ifs, trans))
        {
            if (total.isbn() == trans.isbn())
            {
                total.combine(trans);
            }
            else
            {
                print(ofs, total);
                ofs << std::endl;
                total = trans;
            }
        }
        print(ofs, total);
        ofs << std::endl;

        return 0;
    }
    else
    {
        std::cerr << "No data?!" << std::endl;
        return -1;  // indicate failure
    }
}

8.8

#include <iostream>
#include <string>
#include <fstream>
#include "../ch07_Classes/Sales_data_ex26.h"

int main(int argc, char **argv)
{
    std::ifstream ifs(argv[1]);
    std::ofstream ofs(argv[2], std::ofstream::app);

    if(!ifs) return 1;

    Sales_data total(ifs);

    if (!total.isbn().empty())
    {
        Sales_data trans;

        while (read(ifs, trans))
        {
            if (total.isbn() == trans.isbn())
            {
                total.combine(trans);
            }
            else
            {
                print(ofs, total);
                ofs << std::endl;
                total = trans;
            }
        }
        print(ofs, total);
        ofs << std::endl;

        return 0;
    }
    else
    {
        std::cerr << "No data?!" << std::endl;
        return -1;  // indicate failure
    }
}

8.9

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

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

int main()
{
    std::istringstream istrs("aa\nbb\ncc dd");
    iofunction(istrs);

    std::string s1;
    while(std::cin >> s1)
        std::cout << s1 << std::endl;

    return 0;
}

8.10

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

using namespace std;

int main()
{
    vector<string> v1;
    ifstream is("book_sales");
    string buf;

    if(!is)
    {
        cerr << "open error" << endl;
        return -1;
    }

    while(getline(is, buf))
        v1.push_back(buf);

    for(const auto &s : v1)
    {
        // cout << s << endl;
        istringstream iss(s);
        while(iss >> buf)
            cout << buf << endl;
    }

    return 0;
}

8.11

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

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

    return 0;
}

8.12

string和vector可以自己初始化，并不会出现未定义的情况。

8.13

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

using namespace std;

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

bool valid(const string &s)
{
    for(const auto c : s)
        if(!isdigit(c)) return false;
    return true;
}

string format(const string &s)
{
    return s;
}

int main()
{
    string line, word;
    vector<PersonInfo> people;
    istringstream record;
    ifstream ifs("personinfo");
    ofstream ofs("personinfo_new");

    while(getline(ifs, 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 &person : people)
    {
        ostringstream formatted, badNums;
        for(const auto &ph : person.phones)
        {
            if(!valid(ph))
            {
                badNums << " " << ph;
            }else
                formatted << " " << format(ph);
        }
        if(badNums.str().empty())
            ofs << person.name << " " << formatted.str() << endl;
        else
            cerr << " input error: " << person.name << " invalid number(s)" << badNums.str() << endl;
    }

    return 0;
}