[問題] C++ STL priority_queue

[singlovesong (~"~)]

這是在C++ library 看到對STL裡面 priority_queue的敘述



template < class T, class Container = vector<T>,
           class Compare = less<typename Container::value_type> >
class priority_queue;




Where the template parameters have the following meanings:
T: Type of the elements.
Container: Type of the underlying container object used to store and access
the elements.
Compare: Comparison class: A class such that the expression comp(a,b), where
comp is an object of this class and a and b are elements of the container,
returns true if a is to be placed earlier than b in a strict weak ordering
operation. This can either be a class implementing a function call operator
or a pointer to a function. This defaults to less<T>, which returns the same
as applying the less-than operator (a<b).
The priority_queue object uses this expression when an element is inserted or
removed from it (using push or pop, respectively) to grant that the element
popped is always the greater in the priority queue.


－---------------------

我想應該是小弟英文不太好 看不懂它到底在說啥= =

綠色那段好像事再說 cmp(a,b) function 裡面 return true 就代表 左邊的要

to be placed earlier then 右邊的

這給我的感覺像是如果我寫一個 Test class

然後在Test 裡面寫下

bool operator() (const Test& a , const Test& b){
        if(a.value < b.value)
                return true;
        return false;
}

的話 priority 的順序應該是從小的value到大的value才對 = =

但是下面又說 operator(a<b) 會是從大到小排列

這樣讓我要記用法以後要寫的時候會有點confused 到底該return 啥 = =

是我英文不好還是怎樣呢??@@

謝謝!

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推 legnaleurc:priority queue 會從最大的開始 pop
→ legnaleurc:而所謂"最大"的依據就是根據傳入的 comp
→ legnaleurc:你不用管它是由小排到大還是由大排到小
→ legnaleurc:確定 小值 < 大值 的核算結果是 ture 就行
→ loveme00835:有 < 就可以實作 >=、>、<=、==、!==, 你只需要知道
→ loveme00835:functor是怎麼被使用即可, 不想死背的話可以去研究一
→ loveme00835:下原始碼
→ singlovesong:謝謝! 所以我要從小的pop 就是 小<大 return false
→ singlovesong:所以我還是不太了解 到底return甚麼是左邊的會先被po
→ singlovesong:p... 跟qsort 的return 概念好像不太一樣@@@???
→ singlovesong:            ^compare function
推 legnaleurc:當 comp(a,b) == true 時代表 a 的 priority 比 b 低
→ legnaleurc:注意 "strict weak ordering"
→ singlovesong:!!!! 謝謝 果然是英文不好的原因XD