C++ 在 map<pair, int> 上使用 find
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Using find on map<pair, int>
提问by Jon
How do you use find with a const_iteratorif you have a map defined as
const_iterator如果您将地图定义为，您如何使用 find 和 a
typedef std::pair<int, int> MyPair;
map<MyPair, int> MyMap;
with the pairdefined as the key.
以pair定义为键。
If it was just map<int, int>, I know how to use a const_iteratorlike
如果只是map<int, int>，我知道如何使用const_iterator赞
typedef map<int, int> MyMap;
MyMap::const_iterator it =
MyMap.find(0);
// etc..
回答by Jon
If you are not using C++11, the most convenient is to also do a typedeffor the map type:
如果你没有使用 C++11，最方便的是也typedef为 map 类型做一个：
typedef std::map<MyPair, int> map_type;
And then
进而
map_type::const_iterator it = MyMap.find(make_pair(0, 0));
(I also changed the parameter passed to find, as a bare intis not compatible with your map).
（我还更改了传递给 的参数find，因为裸int图与您的地图不兼容）。
If you are using C++11, you can also do simply
如果您使用的是 C++11，您也可以简单地做
auto it = MyMap.find(make_pair(0, 0));
回答by Chad
Find takes a key type of your map, so in this case you need to create a std::pairthat you want to use in the lookup. Here's a short example:
Find 采用地图的键类型，因此在这种情况下，您需要创建std::pair要在查找中使用的类型。这是一个简短的例子：
#include <map>
#include <string>
#include <iostream>
using namespace std;
int main()
{
std::map<std::pair<int, int>, std::string> m;
m.insert(make_pair(make_pair(0, 0), "Hello"));
m.insert(make_pair(make_pair(1, 0), "There"));
auto res = m.find(make_pair(0,0));
if(res != m.end())
{
cout << res->second << "\n";
}
}
回答by Debasis
There compilation issue in the above code. Please find the correct one as below:
上面的代码有编译问题。请找到正确的如下：
#include <map>
#include <string>
#include <iostream>
using namespace std;
int main()
{
std::map<std::pair<int, int>, std::string> m;
std::map<std::pair<int, int>, std::string>::iterator res;
m.insert(std::make_pair(make_pair(0, 0), "Hello"));
m.insert(std::make_pair(make_pair(1, 0), "There"));
res = m.find(make_pair(0,0));
if(res != m.end())
{
cout << res->second << "\n";
}
}
回答by EnzoGuerra
think you could use
认为你可以使用
std::map<std::pair<int, int>, std::string> m = {
{{ 0, 0 }, "Hello" },
{{ 1, 0 }, "There" },
};
instead of
代替
m.insert(std::make_pair(make_pair(0, 0), "Hello"));
m.insert(std::make_pair(make_pair(1, 0), "There"));
