/ Users / user1 / tests / test22.cpp:318:19:错误:constexpr变量'leftSize'必须通过常量表达式初始化constexpr size_t leftSize = GetLeftSize(array);^ ~~~~~~~~~~~~~~~~~~/Users/user1/tests/test22.cpp:327:27:注意:在此处实例化功能模板特化“ QuickSort”时需要constexpr auto array13 = QuickSort(array12);^/Users/user1/tests/test22.cpp:318:42:注意:在常量表达式中不允许读取非constexpr变量“数组”constexpr size_t leftSize = GetLeftSize(array);^/Users/user1/tests/test22.cpp:318:42:注意:在调用“ array(array)”时/Users/user1/tests/test22.cpp:319:26:错误:非类型模板参数不是常量表达式constexpr std :: array left = QuickSort(SliceLeft(array));^ ~~~~~~~~/Users/user1/tests/test22.cpp:319:26:注意:“ leftSize”的初始化程序不是常量表达式/Users/user1/tests/test22.cpp:318:19:注意:在此声明constexpr size_t leftSize = GetLeftSize(array);^/Users/user1/tests/test22.cpp:327:17:错误:constexpr变量'array13'必须通过常量表达式初始化constexpr auto array13 = QuickSort(array12);^ ~~~~~~~~~~~~~~~~~~
这是我的代码:
#include <array>
template<typename T, size_t N>
constexpr size_t GetLeftSize(const std::array<T, N> array)
{
T f = array[0];
size_t n = 1;
for (size_t i = 1; i < N; i ++)
if (array[i] <= f)
n ++;
return n;
}
// Get Left Slice
template<typename T, size_t N, size_t L>
constexpr std::array<T, L> SliceLeft(const std::array<T, N> array)
{
std::array<T, L> result{};
for (size_t i = 0; i < L; i ++)
result[i] = array[i];
return result;
}
// Get Right Slice
template<typename T, size_t N, size_t R>
constexpr std::array<T, R> SliceRight(const std::array<T, N> array)
{
std::array<T, R> result{};
for (size_t i = 0; i < R; i ++)
result[i] = array[N - i];
return result;
}
// Link Sclice
template<typename T, size_t L, size_t R>
constexpr std::array<T, L + R> LinkSlice(const std::array<T, L> left, const std::array<T, R> right)
{
std::array<T, L + R> result{};
for (size_t i = 0; i < L; i ++)
result[i] = left[i];
for (size_t i = 0; i < L; i ++)
result[L + i] = right[i];
return result;
}
// Quick sort function
template<typename T, size_t N>
constexpr const std::array<T, N> QuickSort(const std::array<T, N> array)
{
if (N <= 1)
return array;
constexpr size_t leftSize = GetLeftSize(array);
constexpr std::array<T, leftSize> left = QuickSort(SliceLeft<T, N, leftSize>(array));
constexpr std::array<T, N - leftSize> right = QuickSort(SliceRight<T, N, N - leftSize>(array));
return LinkSlice(left, right);
}
int main()
{
constexpr std::array<int, 6> array12{7, 9, 3, 6, 1, 19};
constexpr auto array13 = QuickSort(array12);
return 0;
}
array
函数中的参数QuickSort
不是constexpr变量,尽管它将使用constexpr参数array12
进行初始化,因此您不能使用它来初始化constexpr变量leftSize
。实际上,constexpr函数可以修改其参数,因此您可以像执行普通函数一样实现QuickSort
:
#include <array>
template<typename T, std::size_t N>
constexpr void QuickSort(std::array<T, N> &array, std::size_t low, std::size_t high)
{
if (high <= low) return;
auto i = low, j = high + 1;
auto key = array[low];
for (;;) {
while (array[++i] < key) if (i == high) break;
while (array[--j] > key) if (j == low) break;
if (i >= j) break;
auto tmp = array[i];
array[i] = array[j];
array[j] = tmp;
}
auto tmp = array[low];
array[low] = array[j];
array[j] = tmp;
QuickSort(array, low, j - 1);
QuickSort(array, j + 1, high);
}
template<typename T, std::size_t N>
constexpr std::array<T, N> QuickSort(std::array<T, N> array)
{
QuickSort(array, 0, N - 1);
return array;
}
int main()
{
constexpr std::array<int, 6> array12{7, 9, 3, 6, 1, 19};
constexpr auto array13 = QuickSort(array12);
return 0;
}
还要注意,由于C ++ 20,std::sort
已经是constexpr。