c++ - 无法递归创建 C++ 数组

Question

我想测试一个递归方法，下面的代码有一个编译错误。我已经仔细检查了下标变量，它们应该是正确的。我真的想不通，有人可以帮我吗？

#include <iostream>
#include <array>
using namespace std;

template <typename T, size_t Size>
void fn(array<T, Size>& data) { 
   const size_t begin{0};
   const size_t end{Size-1};
   const size_t leftUpper{(begin+end)/2};
   const size_t rightLower{leftUpper+1};

   if (data.size() > 1 ) { 
      array<T, end+1-rightLower> right; 
      cout << "Right: " << end+1-rightLower << endl;   
      fn(right);
   }
}

int main() {
   array<int, 5> test;
   fn(test);
} 

编译错误是:

$ g++ -std=c++14 GuessNumber.cpp -o test
In file included from GuessNumber.cpp:2:0:
/usr/lib/gcc/x86_64-pc-cygwin/7.3.0/include/c++/array: In instantiation of ‘struct std::array<int, 2305843009213693952>’:
GuessNumber.cpp:15:9:   recursively required from ‘void fn(std::array<_Tp, _Nm>&) [with T = int; long unsigned int Size = 2]’
GuessNumber.cpp:15:9:   required from ‘void fn(std::array<_Tp, _Nm>&) [with T = int; long unsigned int Size = 5]’
GuessNumber.cpp:21:11:   required from here
/usr/lib/gcc/x86_64-pc-cygwin/7.3.0/include/c++/array:94:12: error: size of type ‘std::array<int, 2305843009213693952>’ is too large (‘9223372036854775808’ bytes)
     struct array
            ^~~~~

Answer 1

尝试这个:

#include <iostream>
#include <array>
using namespace std;

// the function contains its body just because looks like 
// you want to implement some other logic there
template <typename T>
void fn(array<T, 2ul>& data) {
      const size_t Size = 2;
      const size_t begin{0};
      const size_t end{Size-1};
      const size_t leftUpper{(begin+end)/2};
      const size_t rightLower{leftUpper+1};
      array<T, end+1-rightLower> right; 
      cout << "Right: " << end+1-rightLower << endl;   
}

template <typename T>
void fn(array<T, 1ul>& data) {
}

template <typename T>
void fn(array<T, 1ul>& data) {
      const size_t Size = 1;
      const size_t begin{0};
      const size_t end{Size-1};
      const size_t leftUpper{(begin+end)/2};
      const size_t rightLower{leftUpper+1};
      array<T, end+1-rightLower> right; 
      cout << "Right: " << end+1-rightLower << endl;   
}

template <typename T, size_t Size>
void fn(array<T, Size>& data) { 
   const size_t begin{0};
   const size_t end{Size-1};
   const size_t leftUpper{(begin+end)/2};
   const size_t rightLower{leftUpper+1};

   if (data.size() > 1 ) { 
      array<T, end+1-rightLower> right; 
      cout << "Right: " << end+1-rightLower << endl;   
      fn(right);
   }
}

int main() {
   array<int, 5> test;
   fn(test);
} 

您的代码不是有条件地编译的。 if当您执行模板魔术时，s 不会像您期望的那样工作。另一个例子是 here