实施例代码TEST.CPP错误使用std实例化的std ::阵列时,阵列:: ::大小
#include <array>
#include <string>
int main()
{
// OK
const std::array<int, 2> array_int = {42, 1337};
std::array<float, array_int.size()> array_float_ok;
// Error
const std::array<std::string, 2> array_string = {"foo", "bar"};
std::array<float, array_string.size()> array_float_error;
return 0;
}
使用g ++编译4.8.4(Ubuntu的14.04)
g++ -Wall -std=c++0x test.cpp -o test
提供了以下错误信息
test.cpp: In function ‘int main()’:
test.cpp:14:39: error: call to non-constexpr function ‘constexpr std::array<_Tp, _Nm>::size_type std::array<_Tp, _Nm>::size() const [with _Tp = std::basic_string<char>; long unsigned int _Nm = 2ul; std::array<_Tp, _Nm>::size_type = long unsigned int]’
std::array<float, array_string.size()> array_float_error;
^
In file included from test.cpp:1:0:
/usr/include/c++/4.8/array:162:7: note: ‘constexpr std::array<_Tp, _Nm>::size_type std::array<_Tp, _Nm>::size() const [with _Tp = std::basic_string<char>; long unsigned int _Nm = 2ul; std::array<_Tp, _Nm>::size_type = long unsigned int]’ is not usable as a constexpr function because:
size() const noexcept { return _Nm; }
^
/usr/include/c++/4.8/array:162:7: error: enclosing class of constexpr non-static member function ‘constexpr std::array<_Tp, _Nm>::size_type std::array<_Tp, _Nm>::size() const [with _Tp = std::basic_string<char>; long unsigned int _Nm = 2ul; std::array<_Tp, _Nm>::size_type = long unsigned int]’ is not a literal type
/usr/include/c++/4.8/array:81:12: note: ‘std::array<std::basic_string<char>, 2ul>’ is not literal because:
struct array
^
/usr/include/c++/4.8/array:81:12: note: ‘std::array<std::basic_string<char>, 2ul>’ has a non-trivial destructor
test.cpp:14:39: error: call to non-constexpr function ‘constexpr std::array<_Tp, _Nm>::size_type std::array<_Tp, _Nm>::size() const [with _Tp = std::basic_string<char>; long unsigned int _Nm = 2ul; std::array<_Tp, _Nm>::size_type = long unsigned int]’
std::array<float, array_string.size()> array_float_error;
^
test.cpp:14:40: note: in template argument for type ‘long unsigned int’
std::array<float, array_string.size()> array_float_error;
^
test.cpp:14:59: error: invalid type in declaration before ‘;’ token
std::array<float, array_string.size()> array_float_error;
^
test.cpp:9:39: warning: unused variable ‘array_float_ok’ [-Wunused-variable]
std::array<float, array_int.size()> array_float_ok;
^
test.cpp:14:42: warning: unused variable ‘array_float_error’ [-Wunused-variable]
std::array<float, array_string.size()> array_float_error;
^
有人可以解释这个错误吗?为什么第一个例子工作,而第二个例子不能编译?
定欺骗 - 已经看到了这个问题几次最近 –
[constexpr的和古怪的错误]的可能的复制(http://stackoverflow.com/questions/9607279/constexpr-and-bizzare-error) – mindriot
[在编译时获取std :: array中元素的数量]的可能重复(http://stackoverflow.com/questions/16866033/getting-the-number-of-elements-in-stdarray-at-compile-时间) – sergej