1、clamp
clamp：区间限定函数
int64_t a = Clamp(a, MIN_VALUE, MAX_VALUE);#include <iomanip>
#include <iostream>
#include <sstream>
int main()
{
std::cout << "no setw: [" << 42 << "]\n"
<< "setw(6): [" << std::setw(6) << 42 << "]\n"
<< "no setw, several elements: [" << 89 << 12 << 34 << "]\n"
<< "setw(6), several elements: [" << 89 << std::setw(6) << 12 << 34 << "]\n";
std::istringstream is("hello, world");
char arr[10];
is >> std::setw(6) >> arr;
std::cout << "Input from \"" << is.str() << "\" with setw(6) gave \""
<< arr << "\"\n";
}2、difftime
计算秒维度的两个时间的差距
#include <stdio.h>
#include <time.h>
int main(void)
{
time_t now = time(0);
struct tm beg = *localtime(&now);
// set beg to the beginning of the month
beg.tm_hour = 0,
beg.tm_min = 0,
beg.tm_sec = 0,
beg.tm_mday = 1;
double seconds = difftime(now, mktime(&beg));
printf("%.f seconds have passed since the beginning of the month.\n", seconds);
return 0;
}3、std::stable_sort
按非降序对 [first， last] 范围内的元素进行排序。保证保留相等元素的顺序。
如果对于任何迭代器，它指向序列和任何非负整数 n，使得它 + n 是指向序列元素的有效迭代器，则序列相对于比较器 comp 进行排序，comp（*(it + n）、*it）（或 *（it + n） < *it） 的计算结果为 false。
#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
struct Employee
{
int age;
std::string name; // Does not participate in comparisons
};
bool operator<(const Employee& lhs, const Employee& rhs)
{
return lhs.age < rhs.age;
}
int main()
{
std::vector<Employee> v{
{108, "Zaphod"}, {32, "Arthur"}, {108, "Ford"}};
std::stable_sort(v.begin(), v.end());
for (const Employee& e : v)
std::cout << e.age << ", " << e.name << '\n';
} std::stable_sort(match_docs.begin(), match_docs.end(),
[&ref_struct](const MatchDoc &lhs, const MatchDoc &rhs) {
int64_t l_level = ref_struct.level_ref->get(lhs);
int64_t r_level = ref_struct.level_ref->get(rhs);
float l_score = ref_struct.score_ref->get(lhs);
float r_score = ref_struct.score_ref->get(rhs);
if (l_level == r_level) {
return l_score >= r_score;
} else {
return l_level > r_level;
}
});4、resize
重新指定vector的大小
#include <vector>
#include <iostream>
void print(auto rem, const std::vector<int>& c)
{
for (std::cout << rem; const int el : c)
std::cout << el << ' ';
std::cout << '\n';
}
int main()
{
std::vector<int> c = {1, 2, 3};
print("The vector holds: ", c);
c.resize(5);
print("After resize up to 5: ", c);
c.resize(2);
print("After resize down to 2: ", c);
c.resize(6, 4);
print("After resize up to 6 (initializer = 4): ", c);
}5、std::vector<T,Allocator>::insert
vector的插入函数
#include <iostream>
#include <iterator>
#include <vector>
void print(int id, const std::vector<int>& container)
{
std::cout << id << ". ";
for (const int x : container)
std::cout << x << ' ';
std::cout << '\n';
}
int main ()
{
std::vector<int> c1(3, 100);
print(1, c1);
auto it = c1.begin();
it = c1.insert(it, 200);
print(2, c1);
c1.insert(it, 2, 300);
print(3, c1);
// `it` no longer valid, get a new one:
it = c1.begin();
std::vector<int> c2(2, 400);
c1.insert(std::next(it, 2), c2.begin(), c2.end());
print(4, c1);
int arr[] = {501, 502, 503};
c1.insert(c1.begin(), arr, arr + std::size(arr));
print(5, c1);
c1.insert(c1.end(), {601, 602, 603});
print(6, c1);
}6、 std::stringstream
用来进行流的输入、输出和输入输出操作
std::stringstream sstream;
sstream.precision(4);
sstream << basic_score << ","
<< basic_score<< ","
<< qd_ctr_24h << "," << qd_ctr_7d << ","
<< log_qd_clk_24h << "," << log_qd_clk_7d;
std::string features = sstream.str();7、参考文献
std::vector<T,Allocator>::resize - cppreference.com
difftime() function in C++ - GeeksforGeeks
std::time_t - cppreference.com
std::stable_sort - cppreference.com
