如何在cpp的main()中正确调用此模板函数，该函数使用时间库将数字转换为日期

Question

如何在cpp的main((中正确调用此模板函数，该函数使用时间库将数字转换为日期？

#include <iostream>
#include <chrono>
#include <tuple>

//using namespace std;
// Returns year/month/day triple in civil calendar
// Preconditions:  z is number of days since 1970-01-01 and is in the range:
//                   [numeric_limits<Int>::min(), numeric_limits<Int>::max()-719468].
template <class Int>
constexpr
std::tuple<Int, unsigned, unsigned>
civil_from_days(Int z) noexcept
{
static_assert(std::numeric_limits<unsigned>::digits >= 18,
"This algorithm has not been ported to a 16 bit unsigned integer");
static_assert(std::numeric_limits<Int>::digits >= 20,
"This algorithm has not been ported to a 16 bit signed integer");
z += 719468;
const Int era = (z >= 0 ? z : z - 146096) / 146097;
const unsigned doe = static_cast<unsigned>(z - era * 146097);          // [0, 146096]
const unsigned yoe = (doe - doe/1460 + doe/36524 - doe/146096) / 365;  // [0, 399]
const Int y = static_cast<Int>(yoe) + era * 400;
const unsigned doy = doe - (365*yoe + yoe/4 - yoe/100);                // [0, 365]
const unsigned mp = (5*doy + 2)/153;                                   // [0, 11]
const unsigned d = doy - (153*mp+2)/5 + 1;                             // [1, 31]
const unsigned m = mp < 10 ? mp+3 : mp-9;                            // [1, 12]
return std::tuple<Int, unsigned, unsigned>(y + (m <= 2), m, d);
}


int main(){
std::cout<< civil_from_days(15432)<<'n';
}

这给出了这个或这个(相同的(编译器错误。

代码来自Howard Hinnant

Answer 1

对函数的调用不是问题所在。您得到的错误(应该包括在问题中(是因为元组没有预定义的输出运算符。不过，您可以打印个人成员：

int main(){
auto res = civil_from_days(15432);
std::cout<< std::get<0>(res)<<'n';
std::cout<< std::get<1>(res)<<'n';
std::cout<< std::get<2>(res)<<'n';
}