我想创建一个 C++ 类,在其中可以添加类型(int、long、double、string)的成员。我对 C++ 模板编程非常陌生。
我一直在遵循本指南:https://eli.thegreenplace.net/2014/variadic-templates-in-c/对于可变数据结构。但是我如何输入类型(int、long 等)及其值并将该成员添加到我的类中?
例如,如果这是我定义元组类的方式:
template <class... Ts> struct tuple {};
template <class T, class... Ts>
struct tuple<T, Ts...> : tuple<Ts...> {
tuple(T t, Ts... ts) : tuple<Ts...>(ts...), tail(t) {}
T tail;
};
然后我想在运行时获取输入并且:
while(cin>>type) {
cin>>value;
// add type and value to my class
}
输入可以是 int 3 double 3.5 string hello
。
我的类(class)应该是这种情况tuple<int, double, std::string> t(3, 3.5, "hello")
.
有没有办法使用模板编程来实现这一点?
最佳答案
如果您确实想使用静态类型,例如 std::tuple<int, int, char, int>
基于 cin
的信息然后你的编译器必须在编译时“准备”所有可能的路径。取决于类型数量N
最大长度s
有Nˢ
不同的可能性,即可能性的数量随着最大长度s
呈指数增长。对于非常小的N
和s
这可行。由于您可能更喜欢另一种方法(没有静态类型,例如 std::tuple<int, int, char, int>
),我准备了一个仅处理类型的 C++17 示例。
#include <cstdint>
#include <iostream>
#include <tuple>
template<
class F,
class Tuple=std::tuple<>
>
auto tuplify_cin_and_call(
F f,
Tuple tuple=Tuple{}
) {
constexpr std::size_t max_tuple_size = 6;
std::cout << __PRETTY_FUNCTION__ << std::endl;
if constexpr(1 + std::tuple_size<Tuple>::value < max_tuple_size) {
std::cout << "`int`|`char` to append or `done` to finish: " << std::flush;
std::string input{};
std::cin >> input;
if(input == std::string{"int"}) {
tuplify_cin_and_call(f, std::tuple_cat(tuple, std::tuple<int>{}));
}
else if(input == std::string{"char"}) {
tuplify_cin_and_call(f, std::tuple_cat(tuple, std::tuple<char>{}));
}
else if(input == std::string{"done"}) {
return f(std::move(tuple));
}
else {
std::cout << "ERROR: invalid input" << std::endl;// `cout` or `cerr` here?
return tuplify_cin_and_call(f, std::move(tuple));
}
}
else {
std::cout << "max size reached. `done` to finish: " << std::flush;
std::string input{};
std::cin >> input;
if(input == std::string{"done"}) {
return f(std::move(tuple));
}
else {
std::cout << "ERROR: invalid input" << std::endl;// `cout` or `cerr` here?
return tuplify_cin_and_call(f, std::move(tuple));
}
}
}
int main() {
tuplify_cin_and_call(
[] (auto tuple) { std::cout << __PRETTY_FUNCTION__ << std::endl; }
);
return 0;
}
输出(包括我的键盘输入):
./main
auto tuplify_cin_and_call(F, Tuple) [with F = main()::<lambda(auto:1)>; Tuple = std::tuple<>]
`int`|`char` to append or `done` to finish: int
auto tuplify_cin_and_call(F, Tuple) [with F = main()::<lambda(auto:1)>; Tuple = std::tuple<int>]
`int`|`char` to append or `done` to finish: char
auto tuplify_cin_and_call(F, Tuple) [with F = main()::<lambda(auto:1)>; Tuple = std::tuple<int, char>]
`int`|`char` to append or `done` to finish: asdf
ERROR: invalid input
auto tuplify_cin_and_call(F, Tuple) [with F = main()::<lambda(auto:1)>; Tuple = std::tuple<int, char>]
`int`|`char` to append or `done` to finish: char char int
auto tuplify_cin_and_call(F, Tuple) [with F = main()::<lambda(auto:1)>; Tuple = std::tuple<int, char, char>]
`int`|`char` to append or `done` to finish: auto tuplify_cin_and_call(F, Tuple) [with F = main()::<lambda(auto:1)>; Tuple = std::tuple<int, char, char, char>]
`int`|`char` to append or `done` to finish: auto tuplify_cin_and_call(F, Tuple) [with F = main()::<lambda(auto:1)>; Tuple = std::tuple<int, char, char, char, int>]
max size reached. `done` to finish: asdf
ERROR: invalid input
auto tuplify_cin_and_call(F, Tuple) [with F = main()::<lambda(auto:1)>; Tuple = std::tuple<int, char, char, char, int>]
max size reached. `done` to finish: done
main()::<lambda(auto:1)> [with auto:1 = std::tuple<int, char, char, char, int>]
关于C++ 模板将某种类型的成员添加到类中,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/47517682/