C++ 等效于 Python 字典
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C++ equivalent of Python dictionaries
提问by Jenny Calisay
I'm currently making a tic-tac-toe program with AI and i'm having a bit of a trouble translating this line of code (python) :
我目前正在使用 AI 制作井字棋程序，但在翻译这行代码 (python) 时遇到了一些麻烦：
RANKS = dict([(4,3), # center = 3
(0,2),(2,2),(6,2),(8,2), # corners = 2
(1,1),(3,1),(5,1),(7,1)]) # sides = 1
into C++
到 C++
any suggestions?
有什么建议？
采纳答案by juanchopanza
The closest match in C++ would be an std::unordered_map<int, int>. This is a hash table mapping intkeys to intvalues.
C++ 中最接近的匹配是std::unordered_map<int, int>. 这是一个将int键映射到int值的哈希表。
#include <unordered_map>
std::unordered_map<int, int> RANKS = {
{ 4, 3 },
{ 0, 2 }, { 2, 2 }, { 6, 2 }, { 8, 2 },
{ 1, 1 }, { 3, 1 }, { 5, 1 }, { 7, 1 }
};
You can access elements using operator[], for example
operator[]例如，您可以使用 访问元素
std::cout << RANKS[0] << std::endl; // prints "2"
Note that the C++ standard library also has the std::mapclass template, which allows you to create a similar but orderedlook-up table std::map<int, int>, with logarithmic look-up and insertion complexity. But python dicts are hash tables, so unordered_mapis a closer match in terms of behaviour.
请注意，C++ 标准库也有std::map类模板，它允许您创建一个类似但有序的查找表std::map<int, int>，具有对数查找和插入复杂性。但是 pythondict是哈希表，因此unordered_map在行为方面更接近。
回答by Captain Obvlious
In C++ this would be a std::unordered_map
在 C++ 中，这将是一个 std::unordered_map
#include <unordered_map>
std::unordered_map<int, int> dict
{
{
{ 4, 3 },
{ 0, 2 }, { 2, 2 }, { 6, 2 }, { 8, 2 },
{ 1, 1 }, { 3, 1 }, { 5, 1 }, { 7, 1 }
}
};
回答by Pradhan
The C++ equivalent of Python's dictis std::map. To initialize a map using a similar syntax, do this:
Python 的 C++ 等价物dict是std::map. 要使用类似的语法初始化地图，请执行以下操作：
std::map<int,int> myMap = {{4,3}, # center = 3
{0,2},{2,2},{6,2},{8,2}, # corners = 2
{1,1},{3,1},{5,1},{7,1}}; # sides = 1
Note that this needs C++11.
请注意，这需要 C++11。
If you cannot use C++11, turn to map_list_ofin Boost.Assign. The example from their page is:
如果您不能使用 C++11，请转到map_list_ofBoost.Assign。他们页面上的例子是：
using namespace boost::assign; // bring 'map_list_of()' into scope
std::map<int,int> next = map_list_of(1,2)(2,3)(3,4)(4,5)(5,6);
回答by Galik
Although a "language equivalent" might me something like an std::unordered_mapyour use case may be more efficiently served with a straight array:
尽管“语言等效”可能类似于std::unordered_map您的用例，但使用直数组可能更有效：
int RANKS[] = {2, 1, 2, 1, 3, 1, 2, 1, 2};
回答by Jerry Coffin
You could use a map or unordered_map for this (and they'd work fine) but given that your keys are a dense set of integers (I.e. all the integers from 0 to N) there are better choices.
您可以为此使用 map 或 unordered_map（并且它们可以正常工作），但鉴于您的键是一组密集的整数（即从 0 到 N 的所有整数），有更好的选择。
I'd probably use an std::arrayinstead. It would look something like this:
我可能会用一个std::array代替。它看起来像这样：
std::array <char, 9> vals = { 2, 1, 2, 1, 3, 1, 2, 1, 2 };
This gives pretty much the same syntax and observable behavior, but will typically save quite a bit of memory and probably CPU time as well.
这提供了几乎相同的语法和可观察的行为，但通常会节省相当多的内存和 CPU 时间。
回答by dlna
The "language equivalent" is:
“语言等效”是：
#include <unordered_map>
std::unordered_map<int, int> RANKS = {
{ 4, 3 },
{ 0, 2 }, { 2, 2 }, { 6, 2 }, { 8, 2 },
{ 1, 1 }, { 3, 1 }, { 5, 1 }, { 7, 1 }
};
In case your variable's name was UPPERCASE is because it was a constant:
如果您的变量名称是大写是因为它是一个常量：
#include <unordered_map>
const std::unordered_map<int, int> RANKS = {
{ 4, 3 },
{ 0, 2 }, { 2, 2 }, { 6, 2 }, { 8, 2 },
{ 1, 1 }, { 3, 1 }, { 5, 1 }, { 7, 1 }
};
