第十七章 标准库特殊设施
17.1
tuple<int, int, int> t{1, 2, 3};
tuple<int, int, int> t1(1, 2, 3);
17.2
tuple<string, vector<string>, pair<string, int>> t;
17.4
typedef tuple<vector<Sales_data>::size_type, vector<Sales_data>::const_iterator, vector<Sales_data>::const_iterator> tup;
vector<tup> findBook(const vector<vector<Sales_data>> &files, const string &book)
{
vector<tup> vec;
for (auto it = files.cebegin(); it != files.cend(); ++it) {
auto found = equal_range(it->cbegin(), it->cend(), book, compareIsbn);
if (found.first != found.second)
vec.push_back(make_tuple(it - files.cbegin(), found.first, found.second));
}
return vec;
}
17.5
typedef pair<vector<Sales_data>::size_type, pair<vector<Sales_data>::const_iterator, vector<Sales_data>::const_iterator>> Pair;
vector<Pair> findbook_pair(const vector<vector<Sales_data>> &files, const string &book)
{
vector<Pair> ret;
for (auto it = files.cbegin(); it != files.cend(); ++it)
{
auto found = equal_range(it->cbegin(), it->cend(), book, compareIsbn);
if (found.first != found.second)
ret.push_back(make_pair(it - files.cbegin(), make_pair(found.first, found.second)));
}
return ret;
}
17.6
struct matches_struct
{
vector<Sales_data>::size_type st;
vector<Sales_data>::const_iterator first;
vector<Sales_data>::const_iterator second;
matches_struct(vector<Sales_data>::size_type s, vector<Sales_data>::const_iterator fi, vector<Sales_data>::const_iterator se): st(s), first(fi), second(se) {}
};
vector<matches_struct> findbook_struct(const vector<vector<Sales_data>> &f, const string &book)
{
vector<matches_struct> 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;
}
17.7
倾向于书中的版本，更简洁、灵活
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)：后六位为100000，前面58位全为0
(b)：后七位为1010101，前面25位全为0
(c)：若bstr包含的字符数多于8位，bv只包含bstr的前八位；否则，bv的前几位将被置零。当然，若出现非0/1的字符，会抛出异常
17.10
bitset<22> b;
int a[] = {1, 2, 3, 5, 8, 13, 21};
for (auto &i : a)
b.set(i);
cout << b << endl;
17.11
template <unsigned N>
class test {
public:
test() = default;
test(unsigned long long &u): b(u) { }
test(string &s): b(s) { }
private:
bitset<N> b;
};
int main()
{
test<10> t1;
test<10> t2;
}
17.12
void set_pos(size_t pos, bool bl = true) //问题编号，真假解答的值
{
b.set(pos, bl);
}
17.13
#include <iostream>
#include <string>
#include <bitset>
using namespace std;
template <unsigned N>
class test {
public:
test() = default;
test(unsigned long long &u): b(u) { }
test(string &s): b(s) { }
void set_pos(size_t pos, bool bl = true) //问题编号，真假解答的值
{
b.set(pos, bl);
}
int get_score(bitset<N> &b1)
{
auto bb = b ^ b1;
bb.flip();
return bb.count();
}
private:
bitset<N> b;
};
bitset<10> set_ans()
{
string s;
cout << "请输入标准答案：";
cin >> s;
bitset<10> ans(s);
return ans;
}
int main()
{
bitset<10> ans = set_ans(); //正确答案
test<10> t;
int cnt = 0, pos;
cout << "请输入你认为正确的位置：";
while (cin >> pos && cnt++ <= 10) {
t.set_pos(pos);
}
cout << "正确的答题数为：" << t.get_score(ans) << endl;
return 0;
}
17.14
#include <iostream>
#include <string>
#include <regex>
using namespace std;
int main()
{
try {
regex r("[[:alnum:]+", regex::icase);
} catch (regex_error e) {
cout << e.what() << "\ncode: " << e.code() << endl;
}
return 0;
}
17.15
#include <iostream>
#include <string>
#include <regex>
using namespace std;
int main()
{
regex r("[[:alpha:]]*[^c]ei[[:alpha:]]*", regex::icase);
string s;
cout << "Please input a word(enter 'q' to quit!): " << endl;
while(cin >> s && s != "q")
{
if(std::regex_match(s, r))
cout << s << " is okay!" << endl;
else
cout << s << " is not okay!" <<endl;
cout << "Please input a word(enter 'q' to quit!): " << endl;
}
return 0;
}
17.16
只有一个单词为三个字符时才匹配
17.28
vector<unsigned> func()
{
vector<unsigned> vec;
static default_random_engine e;
static uniform_int_distribution<unsigned> u;
for (auto i = 0; i != 10; ++i)
vec.push_back(u(e));
return vec;
}
17.29
vector<unsigned> func(unsigned seed)
{
vector<unsigned> vec;
static default_random_engine e(seed);
static uniform_int_distribution<unsigned> u;
for (auto i = 0; i != 10; ++i)
vec.push_back(u(e));
return vec;
}
17.30
vector<unsigned> func(unsigned seed, unsigned mmin, unsigned mmax)
{
vector<unsigned> vec;
static default_random_engine e(seed);
static uniform_int_distribution<unsigned> u(mmin, mmax);
for (auto i = 0; i != 10; ++i)
vec.push_back(u(e));
return vec;
}
17.31
每次循环中，分布返回的总是同一个值
17.32
到右大括号时，resp对象将被释放
17.33
#include <iostream>
#include <string>
#include <random>
using namespace std;
string trans1(const string &s1, const string &s2)
{
string s = s1 + s2;
return s;
}
string trans2(const string &s1, const string &s2)
{
string s = s1;
return s;
}
int main()
{
default_random_engine e;
bernoulli_distribution b;
bool bl = b(e);
string ss;
if (bl) ss = trans1("love", "kzw");
else ss = trans2("love", "kzw");
cout << ss << endl;
return 0;
}
17.34
#include <iostream>
#include <string>
#include <iomanip>
using namespace std;
int main()
{
int i = 20;
double d = 10, d1 = 30.1415926;
bool bl = true, bp = false;
cout << boolalpha << bl << " " << bp << " " << noboolalpha << bl << endl;
cout << showbase << 20 << " " << oct << 20 << " " << hex << 20 << endl << dec << noshowbase;
cout << setbase(8) << 20 << " " << 20 << endl;
cout << showpoint << d << noshowpoint << endl;
cout << showpos << i << noshowpos << endl;
cout << d1 << " " << scientific << d1 << " " << fixed << d1 << " " << d1 << endl;
cout << setw(10) << d1 << " " << setprecision(7) << d1 << endl;
return 0;
}
17.35
cout << uppercase << hexfloat << sqrt(2.0) << endl; cout << nouppercase << defaultfloat;
17.36
double d0 = 3.14, d1 = 31.415, d2 = 520.1314, d3 = 11.11223344; cout << "d0: " << setw(12) << d0 << " next col" << endl << "d1: " << setw(12) << d1 << " next col" << endl << "d2: " << setw(12) << d2 << " next col" << endl << "d3: " << setw(12) << d3 << " next col" << endl;
17.37
当未遇到分隔符时，若已读取的字符数超过了size - 1时（下面的程序就是9），就会结束循环
但若遇到分隔符时，前面读取的字符数还未超过size - 1时，会打印该行（如空行），然后开始读取开始下一行（读取的字符数会清0）
小结：要想读取完整，那么字符数组和size都要设置的足够大，大到每一次读取可以遇到分隔符。
#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>
#include <cmath>
using namespace std;
int main()
{
ifstream in("data.txt");
char str[100];
do{
in.getline(str, 10, '\n');
cout << str << endl;
} while(in);
return 0;
}
17.38
#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>
#include <cmath>
using namespace std;
int main()
{
ifstream in("data.txt");
char str[100];
do{
//谨记上一题的教训，size应设置得足够大，至少大于最长的单词的长度
in.getline(str, 30, ' '); //单词应该以空格分隔
cout << str << endl;
} while(in);
return 0;
}
17.39
#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>
#include <cstdlib>
#include <cmath>
using namespace std;
int main()
{
fstream ios("data.txt", fstream::ate | fstream::in | fstream::out);
if (!ios) {
cerr << "Unable to open file!" << endl;
return EXIT_FAILURE;
}
auto endMark = ios.tellg();
ios.seekg(0, fstream::beg);
string line;
size_t cnt = 0;
while (ios && ios.tellg() != endMark && getline(ios, line)) {
cnt += line.size() + 1;
auto mark = ios.tellg();
// ifstream::pos_type mark = ios.tellg();
ios.seekp(0, fstream::end);
ios << cnt;
if (mark != endMark) ios << " ";
ios.seekg(mark);
}
ios.seekp(0, fstream::end);
ios << endl;
return 0;
}
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