std::list c 数组
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array of std::list c
提问by Marco Pietrosanto
I can't find any human explaination for this: how can I create an array of lists like
我找不到对此的任何人工解释：如何创建一个列表数组，例如
std::list<int> mylist[size] ?
If I put this in my program it compiles but creates some problems since it doesn't execute any code (the rest of the code works just fine if I write mylist w/out [size])
如果我把它放在我的程序中，它会编译但会产生一些问题，因为它不执行任何代码（如果我写 mylist w/out [size]，其余的代码工作得很好）
I was reading somewhere that using primitive arrays of C is not recommended; what are the alternatives?
我在某处读到不推荐使用 C 的原始数组；有哪些选择？
Thanks sorry for newbness
谢谢 对不起
回答by Kevin Anderson
Your declaration is incorrect, and not supported in C++. You're trying to declare a variable-sized array at run-time, which IS a C99 feature, but is not in C++. See here: Array size at run time without dynamic allocation is allowed?
您的声明不正确，并且在 C++ 中不受支持。您正在尝试在运行时声明一个可变大小的数组，这是 C99 功能，但不在 C++ 中。请参阅此处：允许运行时没有动态分配的数组大小？
You have this:
你有这个：
std::list<int> mylist[size]
What you need is this:
你需要的是这个：
std::list<int> mylist[] = new std::list<int>[size];
But this is still a bad idea, as you need to de-allocate it later with delete []. As others have said, you can do it a couple of different ways, all of which are better for c++:
但这仍然是一个坏主意，因为您稍后需要使用delete []. 正如其他人所说，您可以通过几种不同的方式来实现，所有这些方式都更适合 C++：
std::list< std::list< int > > myListOfLists; // Linked list of linked lists
std::vector< std::list< int > > myVectorOfLists; // Better, a vector is more like an array
std::array<std::list<int>, 10> this_would_do; // From above, only works if you know the array size at compile-time
I hope this helps and is clear for you.
我希望这对您有所帮助并且很清楚。
回答by sehe
More specifically,
进一步来说，
#include <array>
#include <list>
int main() {
std::array<std::list<int>, 10> this_would_do;
}
回答by P0W
//Codes // | Being Human
typedef list<int> L; // | L is now "alias" for list of integers
const int arr_size=100; // | array needs a constant size, list don't
array<L,arr_size> myArrayOfList; // | An Array as elements L
list<L> myListOfList; // | A List of elements L
//A STL list is doubly linked list
回答by Ivan Mushketyk
回答by A.B.
The syntax to declare a list is as follows
声明列表的语法如下
std::list<T> my_list;
T is a placeholder for any type, including another list, so you can replace T with std::list<int>which gives the following
T 是任何类型（包括另一个列表）的占位符，因此您可以将 T 替换std::list<int>为以下内容
std::list<std::list<int>> my_list;
That declares a list that can hold lists that can hold integers. Note that some compilers may complain about >>, in that case change it to > >
这声明了一个可以容纳可以容纳整数的列表的列表。请注意，某些编译器可能会抱怨>>，在这种情况下将其更改为> >
回答by Mats Petersson
If you actually have a fixed size (e.g. you are having lists of items that have been given a "score" of 0-9), then using a fixed size array is perfectly fine:
如果您实际上有一个固定大小（例如，您有一个“分数”为 0-9 的项目列表），那么使用固定大小的数组就完全没问题了：
std::list<item> scored_items[10];
Of course, it's a poor idea if you don't know beforehand how many you actually want. Then either std::list < std::list < item > > myLists;or a vector std::vector < std::list < item> my_lists;would be suitable solutions.
当然，如果你事先不知道你真正想要多少，这是一个糟糕的主意。那么要么std::list < std::list < item > > myLists;或向量std::vector < std::list < item> my_lists;将是合适的解决方案。
The "correct" solution depends on what your ultimate goal is.
“正确”的解决方案取决于您的最终目标是什么。
