【C ++ Primer】ch10 习题解答_编写一个名为compareisbn的函数-优快云博客

本文链接：https://blog.youkuaiyun.com/zone_programming/article/details/48249969

本文提供了C++ Primer第10章的练习解答，涉及了Sales_data对象的isbn比较、使用partition函数筛选单词、lambda表达式实现函数、biggies函数重写、以及count_if和unique_copy等标准库算法的应用。同时，讲解了如何从文本文件读取内容并存入vector<string>中。

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声明：部分借鉴github项目：https://github.com/Mooophy/Cpp-Primer/tree/master/ch10

练习 10.12：编写compareIsbn的函数，比较两个Sales_data对象的isbn()的成员

<span style="font-size:18px;">struct Sales_data{
    string isbn;
    Sales_data(string s){
        isbn = s;
    }
};

inline bool compareIsbn(const Sales_data& a, const Sales_data& b)
{
    return a.isbn.size() < b.isbn.size();
}

int main()
{
    Sales_data d1("aa"), d2("aaaa"), d3("aaa"), d4("z"), d5("aaaaz");
    vector<Sales_data> v{ d1, d2, d3, d4, d5 };
    sort(v.begin(), v.end(), compareIsbn);
    for(const auto &elem : v)
        cout << elem.isbn << " ";
    cout << endl;

    return 0;
}</span>

练习10.13 ：标准库定义了partition函数，用此函数划分words。打印长度大于等于5的元素

<span style="font-size:18px;">bool predicate(const string& s)
{
    return s.size() >= 5;
}

int main()
{
    auto v = vector<string>{ "a", "as", "aasss", "aaaaassaa", "aaaaaabba", "aaa" };
    auto pivot = partition(v.begin(), v.end(), predicate);

    for(auto it = v.cbegin(); it != pivot; ++ it)
        cout << *it << endl;

    return 0;
}</span>

练习 10.14：编写一个lambda, 接受两个int, 返回它们的和

<span style="font-size:18px;"><span style="font-size:18px;">auto f = [](int a, int b){return a + b;};
    cout << f(5, 6) << endl;</span></span>

练习 10.15：编写一个lambda, 捕获它所在函数的int,并接受一个int参数，返回二者和。

<span style="font-size:18px;"><strong> </strong>   int p = 10;
    auto f = [p](int a){return p + a;};
    cout << f(5) << endl;</span>

练习10.16：使用lambda编写自己的版本biggies;

<span style="font-size:18px;">void elimDups(vector<string> &vec){
    sort(vec.begin(), vec.end());
    auto new_end = unique(vec.begin(), vec.end());
    vec.erase(new_end, vec.end());
}

void biggies(vector<string> &vec, size_t sz)
{
    elimDups(vec);

    stable_sort(vec.begin(), vec.end(),
        [](string const& lhs, string const& rhs){
            return lhs.size() < rhs.size();
        });
    auto wc = find_if(vec.begin(), vec.end(),
        [sz](string const& s) {
            return s.size() >= sz;
        });
    for_each(wc, vec.end(), [](const string& s){
        cout << s << " ";
    });
    cout << endl;

}

int main()
{
    vector<string> v{"better", "hello", "world", "be", "better"};
    biggies(v, 3);

    return 0;
}</span>

练习10.17：重写10.12的compareIsbn(), 利用lambda实现

<span style="font-size:18px;"><span style="font-size:18px;">struct Sales_data{
    string isbn;
    Sales_data(string s){
        isbn = s;
    }
};

int main()
{
    Sales_data d1("aa"), d2("aaaa"), d3("aaa"), d4("z"), d5("aaaaz");
    vector<Sales_data> v{ d1, d2, d3, d4, d5 };
    sort(v.begin(), v.end(), [](const Sales_data& a, const Sales_data& b)
         {return a.isbn.size() < b.isbn.size();});
    for(const auto &elem : v)
        cout << elem.isbn << " ";
    cout << endl;

    return 0;
}</span></span>

练习 10.18 10.19 重写biggies, partition和stable_partition实现

<span style="font-size:18px;"><span style="font-size:18px;"><span style="font-size:18px;">
void elimdups(vector<string> &vs)
{
    sort(vs.begin(), vs.end());
    auto new_end = unique(vs.begin(), vs.end());
    vs.erase(new_end, vs.end());
}


// ex10.18
void biggies_partition(vector<string> &vs, size_t sz)
{
    elimdups(vs);

    auto pivot = partition(vs.begin(), vs.end(), [sz](const string &s){
        return s.size() >= sz;}
    );

    for(auto it = vs.cbegin(); it != pivot; ++it)
        cout << *it << " ";
}


// ex10.19
void biggies_stable_partition(vector<string> &vs, size_t sz)
{
    elimdups(vs);

    auto pivot = stable_partition(vs.begin(), vs.end(), [sz](const string& s){
        return s.size() >= sz;
    });

    for(auto it = vs.cbegin(); it != pivot; ++it)
        cout << *it << " ";
}


int main()
{
    vector<string> v{
        "the", "quick", "red", "fox", "jumps", "over", "the", "slow", "red", "turtle"
    };

    cout << "ex10.18: ";
    vector<string> v1(v);
    biggies_partition(v1, 4);
    cout << endl;

    // ex10.19
    cout << "ex10.19: ";
    vector<string> v2(v);
    biggies_stable_partition(v2, 4);
    cout << endl;

    return 0;
}</span></span>
</span>

练习 10.20：标准库定义了一个count_if的算法。使用count_if重写程序中统计有多少个单词长度超过6.

<span style="font-size:18px;"><span style="font-size:18px;">    vector<string> vec{"hello", "world", "better", "is", "better", "less", "is", "more"};
    int ans = count_if(vec.begin(), vec.end(), [](string s){ return s.size() >= 5; });
    cout << ans << endl;</span></span>

练习 10.21：编写一个lambda，捕获一个局部int变量，并递减变量值，直至它为0.一旦变量为0，再调用lambda不应该再递减变量。lambda应该返回一个bool值，指出捕获的变量是否为0.

<span style="font-size:18px;">    int index = 7;
    auto check_and_decrement = [&index]() { return -- index ? false : true;};
    while(!check_and_decrement())
        cout << index << " ";
    cout << index << endl;</span>

练习10.22: 重写统计长度小于等于5的单词数量的程序，使用函数代替lambda

<span style="font-size:18px;"><span style="font-size:18px;">bool isBiggerThan5(const string& s, string::size_type sz)
{
    return s.size() > sz;
}

int main()
{
    vector<string> vec{"hello", "world", "better", "is", "better", "less", "is", "more"};
    cout << count_if(vec.begin(), vec.end(), bind(isBiggerThan5, _1, 5)) << endl;

    return 0;
}</span></span>

练习10.24: 给定一个string, 使用bind和check_size在一个int的vector中查找第一个大于string长度的值。

<span style="font-size:18px;">inline auto check_size(const string& s, string::size_type sz) -> bool
{
    return s.size() >= sz;
}

inline auto find_first_greater(vector<int> const& v, string const& s) -> vector<int>::const_iterator
{
    auto lambda = [&](int i) {return i >= 0 && bind(check_size, s, i)();};
    return find_if(v.cbegin(), v.cend(), lambda);
}

int main()
{
    vector<int> v{ -1, -2, 4, 3, 4, 5, 6, 7 };
    string s("test");
    cout << *find_first_greater(v, s) << endl;
}</span>

练习 10.25：编写一个使用partition的biggies版本。使用check_size和bind重写此函数

<span style="font-size:18px;">void elimdups(vector<string> &vs)
{
    std::sort(vs.begin(), vs.end());
    vs.erase(unique(vs.begin(), vs.end()), vs.end());
}

bool check_size(const string &s, string::size_type sz)
{
    return s.size() >= sz;
}

void biggies(vector<string> &words, vector<string>::size_type sz)
{
    elimdups(words);
    auto iter = std::stable_partition(words.begin(), words.end(), bind(check_size, _1, sz));
    for_each(words.begin(), iter, [](const string &s){ std::cout << s << " "; });
}

int main()
{
    std::vector<std::string> v{
        "the", "quick", "red", "fox", "jumps", "over", "the", "slow", "red", "turtle"
    };
    biggies(v, 4);
}</span>

练习 10.27： unique_copy, vector --> list

<span style="font-size:18px;"><strong> </strong><span style="font-size:18px;">   vector<int> v = {2, 3, 1, 1, 4};
    list<int> lst;
    unique_copy(v.begin(), v.end(), back_inserter(lst));
    for_each(lst.begin(), lst.end(), [](const int val){ cout << val << " "; });
    cout << endl;</span></span>

练习 10.29：编写程序，使用迭代器读取一个文本文件，存入一个vector的string中去。

<span style="font-size:18px;">    ifstream in("test.txt");
    istream_iterator<string> in_it(in);
    istream_iterator<string> in_eof;
    vector<string> vec;
    copy(in_it, in_eof, back_inserter(vec));
    // output
    copy(vec.begin(), vec.end(), ostream_iterator<string>(cout, " "));
</span>

练习 10.30: 使用流迭代器、sort和copy从标准输入读取一个整数序列，将其排序，并将结果写到标准输出。

<span style="font-size:18px;">    istream_iterator<int> in_it(cin), eof;
    vector<int> vec(in_it, eof);
    sort(vec.begin(), vec.end());
    copy(vec.begin(), vec.end(), ostream_iterator<int>(cout, " "));
</span>

练习 10.31：改写上题，采用unique_copy,输出不重复元素

<span style="font-size:18px;">    istream_iterator<int> in_it(cin), eof;
    vector<int> vec(in_it, eof);
    sort(vec.begin(), vec.end());
    unique_copy(vec.begin(), vec.end(), ostream_iterator<int>(cout, " "));</span>

练习 10.33：编写程序，输入3个参数，第一个为输入文件，其余二者为分别保存奇数和偶数的文件。

<span style="font-size:18px;">    ifstream in("test.txt");
    ofstream even("even.txt");
    ofstream odd("odd.txt");
    istream_iterator<int> in_it(in), in_eof;
    ostream_iterator<int> os1(even, "\n"), os2(odd, " ");
    for_each(in_it, in_eof, [&os1, &os2](const int i) {
                *(i & 0x1 ? os2 : os1) ++ = i;
             });</span>

练习 10.34：使用reverse_iterator逆序打印一个vector。

<span style="font-size:18px;">    istream_iterator<int> in_iter(cin), eof;
    vector<int> vec(in_iter, eof);
    for(vector<int>::reverse_iterator it = vec.rbegin(); it != vec.rend(); ++ it)
        cout << *it << endl;</span>