如何获得的char []用的std ::地图工作 [英] How to get char[] to work with std::map

问题描述

编辑回答后：

＆LT; 应提供的std ::地图。有关最佳实践的详细信息，请詹姆斯McNellis的答案

在code列入这个问题是写得不好。这只是因为我有SPOJ玩和输入数据是严格有效的。在的std ::字符串办法是什么，我选择了在第一，但它竟然是不够快。

The code included in this question is poorly written. It is just because I am playing with SPOJ and the input data is strictly valid. The std::string approach is what I chose at first, but it turned out to be not fast enough.

感谢您。

我知道我不能使用的char [] 直接与地图，如地图＆LT;的char []，INT＆GT; 。因此，我把它放在一个类。但它仍然可以通过编译。如何处理呢？

I know I cannot use char[] directly with map, such as map<char[], int>. Thus I put it in a class. But it still can go through compilation. How to deal with that?

#include <stdio.h>
#include <map>

using namespace std;

class id {
public:
    char v [30];
};

int main () {
    map<id, int> m;
    id a;
    while (gets(a.v)) {
        m[a]++;
    }
    return 0;
}

---

/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_function.h: In member function ‘bool std::less<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = id]’:
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_map.h:418:   instantiated from ‘_Tp& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const _Key&) [with _Key = id, _Tp = int, _Compare = std::less<id>, _Alloc = std::allocator<std::pair<const id, int> >]’
prog.cpp:15:   instantiated from here
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_function.h:230: error: no match for ‘operator<’ in ‘__x < __y’

这似乎它是与比较，但我仍然在黑暗中。

It seems it has something to do with comparison, but I am still in the dark.

推荐答案

您需要执行＆LT; 运营商

class id {
public:
    char v [30];
    bool operator<(const id &rhs) const{
        return strcmp(v,rhs.v) < 0;
    }
};

编辑：作为一个方面说明你的code是一个做事的非常差的方式。看到一些答案的一个解释这是为什么。

As a side note your code is a very poor way of doing things. See some of the answers for an explanation why.

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