C++ vector 迭代器 nth_element 编译错误

Question

下面的代码将无法编译。第 2 行到最后一行 (nth_element...) 有错误。这似乎与比较器有关。编译器声称“术语不计算为采用 2 个参数的函数”。如何修复编译错误？

    struct Result {
        Result(unsigned int id, double result);
        bool cmp(const Result &a, const Result &b)  const;

        unsigned int id;
        double result;
    };


Result::Result(unsigned int id, double result) {
    this->id = id;
    this->result = result;
}

bool Result::cmp(const Result &a, const Result &b)  const {
    if(a.result < b.result) {
        return true;
    }
    return false;
}

    //25th-percentile
    int index = (int) ((buffer.size()+1.0)/4.0 - 0.499);
    vector<Result>::iterator itrindex = buffer.begin() + index;
    nth_element(buffer.begin(), itrindex, buffer.end(), &Result::cmp);
    double twentyfifthperc = buffer[index].result;

Answer 1

bool cmp(const Result &a, const Result &b)  const;

应该是

static bool cmp(const Result &a, const Result &b);