stl中hash_map的使用

[gisupc]

我采用如下方式定义一个结构体
struct POINT{
double x;
double y;
};
#include<hash_map>
using namespace stdext;

hash_map<int ,POINT> PtHash;
然后想通过hash_map的find函数查找当前点POINT是否与hashmap中的相等，该如何做呢？求指点，谢谢！

[gisupc]

可以参考的例子是http://msdn.microsoft.com/en-us/library/8zz3703d(v=VS.80).aspx

[Eleven]

// hash_map_find.cpp
// compile with: /EHsc
#define _DEFINE_DEPRECATED_HASH_CLASSES 0
#include <hash_map>
#include <iostream>

int main( )
{
   using namespace std;
   using namespace stdext;
   hash_map <int, int> hm1;
   hash_map <int, int> :: const_iterator hm1_AcIter, hm1_RcIter;
   typedef pair <int, int> Int_Pair;

   hm1.insert ( Int_Pair ( 1, 10 ) );
   hm1.insert ( Int_Pair ( 2, 20 ) );
   hm1.insert ( Int_Pair ( 3, 30 ) );

   hm1_RcIter = hm1.find( 2 );
   cout << "The element of hash_map hm1 with a key of 2 is: "
        << hm1_RcIter -> second << "." << endl;

   // If no match is found for the key, end( ) is returned
   hm1_RcIter = hm1.find( 4 );

   if ( hm1_RcIter == hm1.end( ) )
      cout << "The hash_map hm1 doesn't have an element "
           << "with a key of 4." << endl;
   else
      cout << "The element of hash_map hm1 with a key of 4 is: "
           << hm1_RcIter -> second << "." << endl;

   // The element at a specific location in the hash_map can be found 
   // using a dereferenced iterator addressing the location
   hm1_AcIter = hm1.end( );
   hm1_AcIter--;
   hm1_RcIter = hm1.find( hm1_AcIter -> first );
   cout << "The element of hm1 with a key matching "
        << "that of the last element is: "
        << hm1_RcIter -> second << "." << endl;
}
 
  Copy Code 
The element of hash_map hm1 with a key of 2 is: 20.
The hash_map hm1 doesn't have an element with a key of 4.
The element of hm1 with a key matching that of the last element is: 30.
 

MSDN上的例子代码，可以参考一下~

[youngwolf]

你的key是int，却要找一个POINT，设计有问题，非要找的话，只能自己遍历来找。
map的key才是用来查找的。

[buyong]

用hash_map::iterator遍历比较

[gisupc]

[Quote=引用 3 楼 yang79tao 的回复:]

你的key是int，却要找一个POINT，设计有问题，非要找的话，只能自己遍历来找。
map的key才是用来查找的。
[/Quote]
你的意思是将POINT 设置为key才能进行查找是吧！

[youngwolf]

既然是map，当然要使用其高速查找的特性，如果你通过遍历去查找，当然也是能查找的，此时map容器就退化为vector了，甚至比vector效率还差。

每个容器都有自己的优点缺点，如果你非要用其弱点，那就本末倒置了。