collection

1.

#include <algorithm>
#include <iostream>
#include <vector>
 
struct PriceInfo { double price; };
 
int main()
{
    const std::vector<int> data {1, 2, 4, 5, 5, 6};
 
    for (int i = 0; i < 7; ++i)
    {
        // Search first element that is greater than i
        auto upper = std::upper_bound(data.begin(), data.end(), i);
 
        std::cout << i << " < ";
        upper != data.end()
            ? std::cout << *upper << " at index " << std::distance(data.begin(), upper)
            : std::cout << "not found";
        std::cout << '\n';
    }
 
    std::vector<PriceInfo> prices {{100.0}, {101.5}, {102.5}, {102.5}, {107.3}};
 
    for (double to_find : {102.5, 110.2})
    {
        auto prc_info = std::lower_bound(prices.begin(), prices.end(), to_find,
            [](double va,const PriceInfo& info)
            // no known conversion for argument 1 from 'PriceInfo' to 'double'
            {
                return va > info.price;
            });
 
        prc_info != prices.end()
            ? std::cout << prc_info->price << " at index " << prc_info - prices.begin()
            : std::cout << to_find << " not found";
        std::cout << '\n';
    }
}

需要将lambda函数 捕获列表中参数位置互换

auto prc_info = std::lower_bound(prices.begin(), prices.end(), to_find,
            [](const PriceInfo& info, double va)
            {
                return va > info.price;
            });

2.

// 修改时间
   char* t = ctime(&st.st_mtime); // 这个字符串包含最后的换行符
   // printf("%s\n", t);
   
   char* tt;
   strncpy(tt, t, strlen(t) - 1); // 发生段错误
   
   char tt[1024];
   // strncpy(tt, t, sizeof(t) - 1); // Tue May
   strncpy(tt, t, strlen(t) - 1); // Tue May  2 10:15:54 2023
   printf("%s\n", tt);
   

`dest`不能用`char*`的`tt`，只能用`char tt[1024]`；

sizeof只有前半段字符串，strlen才能全部复制

并且char tt[1024]会改变前面变量quanxian的值，在后面加上了tt，而修改成更大的值则正常

3.