可以从命令行参数读取std :: array的维数吗? [英] Can the dimension of std::array be read from command line arguments?

问题描述

我有一个C ++代码，我决定使用 std :: array 而不是 std :: vector ，我希望从命令中读取数组的大小线.

I have a C++ code where I decided to use std::array instead of std::vector and I want the size of the array to be read from command line.

在实践中，可以使用以下代码段进行总结

In practice, this can be summarized with the following snippet

#include <iostream>
#include <array>
#include <sstream>

int main(int argc, char* argv[]){

  std::size_t my_size;
  {
    std::istringstream is{argv[1]};
    is >> my_size;
  }
 
  std::cout << my_size<<std::endl;
  std::array<int,my_size> a;
  return 0;
}

编译器会给出以下错误，这是由于必须在编译时知道 my_size 的事实.

The compiler gives the following error, which is due to the fact that my_size must be known at compile time.

错误:常量表达式中无法使用"my_size"的值
14 |std :: array< int，my_size>一个；

error: the value of ‘my_size’ is not usable in a constant expression
14 | std::array<int,my_size> a;

有什么方法可以让 std :: array 的大小从命令行给出?还是我绝对应该使用其他容器?作为堆上的动态数组或 std :: vector ?

Is there any way to let the size of an std::array to be given from command line? Or should I definitely use other containers? As dynamic arrays on the heap, or std::vector ?

推荐答案

在编译时必须特别知道类型和数组的大小，因此答案是:否.

Types and arrays sizes in particular must be known at compile time, hence the answer is: No.

您可以实现从运行时值到编译时常量的某些映射.

You can implement some mapping from a runtime value to a compile-time constant. Something along the line of

size_t size;
std::cin >> size;
if (size == 10) {
     std::array<int,10> x;
     // use x
} else if (size == 20) [
     std::array<int,20> y;
     // use y
}

但是，这用途非常有限，因为 x 和 y 是不同类型的.如果仅在运行时知道大小，则使用 std :: vector 会更容易.

However, this is of very limited use, because x and y are of different type. When the size is only known at runtime it is easier to use a std::vector.

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