<分区>
我知道我可以用一个常规的可变参数函数来做到这一点,但我想用模板来做到这一点。我的 (C++17) 编译器不会同意它。
#include <cstdint>
unsigned int fct(unsigned int k)
{
return k;
}
template<std::size_t First, std::size_t... Other>
unsigned int fct(unsigned int k)
{
return First * fct<Other...>(k);
}
int main(void)
{
//const auto k = fct<3u, 5u, 7u>(2u);
return 0;
}
以上代码编译正常。但是,如果我选择取消注释 k
的声明,编译将失败并显示以下报告:
foo.cpp: In function ‘int main()’:
foo.cpp:17:13: warning: unused variable ‘k’ [-Wunused-variable]
const auto k = fct<3u, 5u, 7u>(2u);
^
foo.cpp: In instantiation of ‘unsigned int fct(unsigned int) [with long unsigned int First = 7; long unsigned int ...Other = {}]’:
foo.cpp:11:30: recursively required from ‘unsigned int fct(unsigned int) [with long unsigned int First = 5; long unsigned int ...Other = {7}]’
foo.cpp:11:30: required from ‘unsigned int fct(unsigned int) [with long unsigned int First = 3; long unsigned int ...Other = {5, 7}]’
foo.cpp:17:35: required from here
foo.cpp:11:30: error: no matching function for call to ‘fct<>(unsigned int&)’
return First * fct<Other...>(k);
~~~~~~~~~~~~~^~~
foo.cpp:9:14: note: candidate: template<long unsigned int First, long unsigned int ...Other> unsigned int fct(unsigned int)
unsigned int fct(unsigned int k)
^~~
foo.cpp:9:14: note: template argument deduction/substitution failed:
foo.cpp:11:30: note: couldn't deduce template parameter ‘First’
return First * fct<Other...>(k);
~~~~~~~~~~~~~^~~
我怎样才能使这项工作?我认为创建一个非模板 fct()
就可以完成这项工作。