问问std：：map

[zhenzhubaoyou]

typedef std::map<String, Property*, String::FastLessCompare> PropertyRegistry;
PropertyRegistry d_properties;

这个map里一个键对应两个值么？在那个c++ primer里找了半天没找到是啥用法啊？一般都是看到的键值对，都是一对一的啊。请明白的兄台指教！

[chin_chen]

是一对一的，后面的那个是插入时比较用的缺省函数，自己可以定义的。

[wangyaosuper]

第一个参数是key的类型，第二个是对key进行散列的方法。

[BenjaminHuang]

好像没有看到过 std::map 里单项能关联三个值的用法耶 map <String, Property*, String::FastLessCompare>
是不是搞错了?

[lightnut]

template <
class Key,
class Type,
class Traits = less<Key>,
class Allocator=allocator<pair <const Key, Type> >
>
class map



Parameters

Key
The key data type to be stored in the map.

Type
The element data type to be stored in the map.

Traits
The type that provides a function object that can compare two element values as sort keys to determine their relative order in the map. This argument is optional and the binary predicate less<Key> is the default value.

Allocator
The type that represents the stored allocator object that encapsulates details about the map's allocation and deallocation of memory. This argument is optional and the default value is allocator<pair <const Key, Type> >.

[xiaoyisnail]

map有四个模板参数，后面两个有默认值，所以平时一般只用前两个指定key和value类型，第三个是比较函数，第四个是内存分配器，声明如下：

		// TEMPLATE CLASS map
template<class _K, class _Ty, class _Pr = less<_K>,
	class _A = allocator<_Ty> >
class map {
...
};

[waizqfor]

[Quote=引用 4 楼 lightnut 的回复:]
template <
class Key,
class Type,
class Traits = less <Key>,
class Allocator=allocator <pair <const Key, Type> >
>
class map



Parameters

Key
The key data type to be stored in the map.

Type
The element data type to be stored in the map.

Traits
The type that provides a function object that can compare two element values as sort keys to determine the…
[/Quote]
MSDN上有
LZ去看看吧

[yxjiang]

如果是三个的版本话，第三个参数为一个用于比较的函数对象。