在函数内部初始化std :: array [英] Initializing std::array inside a function

问题描述

我想创建一个调整堆栈大小的函数.它将根据max的值创建一个更大或更小的新数组，然后将元素复制到该新数组中.

  void resize(const int& max){std :: array< Item，max>温度for(int i = 0; i< n; i ++){temp.at(i)= a.at(i);}a =温度；} 

我知道这不会运行，因为max不是一个常数表达式.我绝对不知道如何传递一个恒定的int值.我试过了:

void resize(constexpr int& max)//编译器说不能使int arg constexpr

我不想做constexpr void resize，因为我不需要在编译时对函数进行求值，而且该函数也无法正常工作.

注意:我知道如果我使用std :: vector可能会更容易，因为它可以调整大小，但是我想尝试使用std :: array.

我该怎么办?

解决方案

我认为您错误地考虑了编译时常量和运行时常量.您不能以这种方式使用 std :: array .您需要一个大小不是编译时常数的容器，该容器将为 std :: vector .

如果您希望容器的大小在整个运行时保持恒定，则可以依靠自律(即:不要使用 push_back()或 resize()等等.)或者，您可以编写一个包装器类(例如，具有-std :: vector 作为成员的类)并仔细选择此类的方法，以免调整矢量的大小./p>

您也可以使用dynarray，但它已被c ++ 11(和c ++ 14，如果我没记错的话)拒绝了

PS:命名您的方法 resize()然后说您想要常量大小的数组=)很奇怪您确实意识到，如果调用此方法，则实际上是在运行时更改了数组的大小，在这种情况下，为什么不使用std :: vector并对其进行处理呢?

I want to create a function that resizes a stack. It will create a new array with a larger or smaller size depending on the value of max, then copy the elements into that new array.

void resize(const int& max) {
    std::array<Item, max> temp;
    for (int i = 0; i < n; i++) {
        temp.at(i) = a.at(i);
    }
    a = temp;
}

I know this will not run because max is not a constant expression. I absolutely don't know how to pass a constant int value. I tried:

void resize(constexpr int& max) //compiler says cannot make int arg constexpr

I don't want to do constexpr void resize because I don't need the function to be evaluated at compile time, and it didn't work anyway.

Note: I know this might be easier if I used std::vector because it's resizable, but I want to try to experiment with std::array.

What should I do?

解决方案

I think you are mistaking compile-time constant and run-time constant. You cannot use std::array in this way. You want a container whose size is not compile-time constant, and that would be std::vector.

If you want your container's size to be constant throughout the runtime, you can either rely on self discipline (i.e : do not use push_back() or resize() etc..) Or you could write a wrapper class (.i.e a class that has-a std::vector as a member) and choose the methods of this class carefully to never resize the vector.

You can also use dynarray but it has been rejected from c++11 (and c++14 If I recall correctly)

PS: it is quite weird to name your method resize() and then say that you want constant-sized arrays =) You do realize that if you call this method you are indeed changing the size of your array at runtime, in which case why not use std::vector and be done with it ?

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