問(wèn)題描述

感謝C 中的解決方案,現(xiàn)在我想在 C++ 中使用 std::sort 和 vector 來(lái)實(shí)現(xiàn)這一點(diǎn):

Thanks for a solution in C, now I would like to achieve this in C++ using std::sort and vector:

typedef struct
{
  double x;
  double y;
  double alfa;
} pkt;

向量<包>wektor; 使用 push_back() 填充；比較函數(shù):

vector< pkt > wektor; filled up using push_back(); compare function:

int porownaj(const void *p_a, const void *p_b)
{
  pkt *pkt_a = (pkt *) p_a;
  pkt *pkt_b = (pkt *) p_b;

  if (pkt_a->alfa > pkt_b->alfa) return 1;
  if (pkt_a->alfa < pkt_b->alfa) return -1;

  if (pkt_a->x > pkt_b->x) return 1;
  if (pkt_a->x < pkt_b->x) return -1;

  return 0;
}

sort(wektor.begin(), wektor.end(), porownaj); // this makes loads of errors on compile time

要糾正什么?在這種情況下如何正確使用 std::sort?

What is to correct? How to use properly std::sort in that case?

推薦答案

std::sort 采用與 qsort 中使用的比較函數(shù)不同的比較函數(shù).該函數(shù)不返回 –1、0 或 1，而是返回一個(gè) bool 值，指示第一個(gè)元素是否小于第二個(gè)元素.

std::sort takes a different compare function from that used in qsort. Instead of returning –1, 0 or 1, this function is expected to return a bool value indicating whether the first element is less than the second.

您有兩種可能性:為您的對(duì)象實(shí)現(xiàn) operator <；在這種情況下，沒(méi)有第三個(gè)參數(shù)的默認(rèn) sort 調(diào)用將起作用；或者你可以重寫(xiě)上面的函數(shù)來(lái)完成同樣的事情.

You have two possibilites: implement operator < for your objects; in that case, the default sort invocation without a third argument will work; or you can rewrite your above function to accomplish the same thing.

請(qǐng)注意，您必須在參數(shù)中使用強(qiáng)類(lèi)型.

Notice that you have to use strong typing in the arguments.

另外，這里根本不使用函數(shù)也不錯(cuò).相反，使用函數(shù)對(duì)象.這些受益于內(nèi)聯(lián).

Additionally, it's good not to use a function here at all. Instead, use a function object. These benefit from inlining.

struct pkt_less {
    bool operator ()(pkt const& a, pkt const& b) const {
        if (a.alfa < b.alfa) return true;
        if (a.alfa > b.alfa) return false;

        if (a.x < b.x) return true;
        if (a.x > b.x) return false;

        return false;
    }
};

// Usage:

sort(wektor.begin(), wektor.end(), pkt_less());

這篇關(guān)于如何將 std::sort 與結(jié)構(gòu)向量和比較函數(shù)一起使用?的文章就介紹到這了，希望我們推薦的答案對(duì)大家有所幫助，也希望大家多多支持html5模板網(wǎng)！