C++Primer第五版——习题答案详解

Posted 2021-02-13 mered1th

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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。