这是我的测试程序：
#include <iostream>
#include <typeinfo>
using namespace std;
template <typename T>
decltype(auto) foo(T& arg)
{
return arg;
}
int main()
{
const int x = 10;
int & y = const_cast<int&>(foo(x));
y = 20;
cout << "x: " << &x << " " << x << endl;
cout << "y: " << &y << " " << y << endl;
}
输出：
g++ -std=c++17 main.cpp && ./a.out
x: 0x7ffee31f4a6c 10
y: 0x7ffee31f4a6c 20
为什么x的值foo没有更改，即使const int&已将const_cast更改为int& x？
因为从输出中看起来y和 string delimiter = ",";
string sTimeUpper = "2017-04-25 14:16:30.000";
string sTimeLower = "2017-04-25 14:15:30.000";
DateTime TimeUpper = DateTime.Parse(sTimeUpper);
DateTime TimeLower = DateTime.Parse(sTimeLower);
Console.WriteLine($"TimeLower = {TimeLower}");
Console.WriteLine($"TimeUpper = {TimeUpper}");
List<string> res = (File.ReadAllLines(@"TimeStamp.txt")
.Skip(1)
.Select(line => line.Split(delimiter.ToCharArray(), StringSplitOptions.RemoveEmptyEntries))
.Where(fields => DateTime.Parse(fields[3]) > TimeLower && DateTime.Parse(fields[3]) < TimeUpper)
.Select(fields => string.Join(",", fields))
.ToList<string>());
Console.WriteLine("Requested readings:");
foreach (string item in res)
{
Console.WriteLine(item);
}
的两个地址是相同的。