c++ - 自定义排序元组 vector 时出错

Question

我尝试对元组 vector 进行排序，但我遇到了一个奇怪的错误:

typedef std::tuple<const std::string, const std::string, const unsigned int> nodesfound;

std::vector<nodesfound> nf;

fil_vector(nf);

std::sort(nf.begin(), nf.end(), [](nodesfound const &n1, nodesfound const &n2) {
        return std::get<2>(n1) < std::get<2>(n2);
    });

错误是:

/usr/bin/../lib/gcc/x86_64-linux-gnu/5.4.0/../../../../include/c++/5.4.0/tuple:299:17: error: no viable overloaded '='_M_head(*this) = std::forward<_Head>(_M_head(__in));

如果我删除排序行，我的程序就完全没问题了

Answer 1

要使 sort 起作用，元素必须是可分配的；然而，您的元组元素都是 const，因此显然 不可 分配。删除 const:

using nodesfound = std::tuple<std::string, std::string, unsigned>;

std::vector<nodesfound> nf;
fill_vector(nf);
std::sort(
    nf.begin(), nf.end(),
    [](nodesfound const& n1, nodesfound const& n2) {
        return std::get<2>(n1) < std::get<2>(n2);
    }
);

Online Demo