将方法转换为调用该方法的成员函数器对象会导致崩溃

Question

我在一个类中有以下方法：

bool temp_cmp(size_t l, size_t r) const {
    return memcmp(get_next_temp_record(l), get_next_temp_record(r), page_size) < 0;
}

但我需要它作为一个函数对象，所以我重写了它，如下所示：

struct temp_cmp_functor {
    const sorter& _s;
    temp_cmp_functor(sorter& s) : _s(s) {
        std::cout << "ADDR: " << &_s << std::endl;
    }

    bool operator()(size_t l, size_t r) const {
        std::cout << "ADDR AT CALL: " << &_s << std::endl;
        return memcmp(_s.get_next_temp_record(l), _s.get_next_temp_record(r), page_size) < 0;
    }
};
temp_cmp_functor temp_cmp{*this};

现在，后来当我像temp_cmp(idx1, idx2)一样调用它时，我在使用ASAN (函数get_next_temp_record访问类的一些类型为std::vector的字段，但我认为这不应该是相关的)的清理构建中崩溃。

你知道为什么这个改变可能会有问题吗？我正在打印对象的地址，它们在函数器的构造函数中匹配，当operator()被调用时-我认为这没有理由不起作用……对我来说，这两种方式应该是相同的…我遗漏了什么？

以下是ASAN的输出：

/usr/include/c++/9/bits/stl_vector.h:1061:34: runtime error: reference binding to null pointer of   type 'const struct value_type'
../../demos/ip_demo.cc:185:33: runtime error: member access within null pointer of type 'const struct   value_type'
AddressSanitizer:DEADLYSIGNAL
=================================================================
==3862==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000020 (pc 0x00000047a8b4 bp   0x7ffe9e0042c0 sp 0x7ffe9e0042a0 T0)
==3862==The signal is caused by a READ memory access.
==3862==Hint: address points to the zero page.
    #0 0x47a8b3 in std::__uniq_ptr_impl<char, seastar::free_deleter>::_M_ptr() const /usr/include/c++/  9/bits/unique_ptr.h:154
    #1 0x465ac5 in std::unique_ptr<char [], seastar::free_deleter>::get() const /usr/include/c++/9/ bits/unique_ptr.h:612
    #2 0x46635d in std::unique_ptr<char [], seastar::free_deleter>::operator[](unsigned long) const (/  home/onqtam/seastar/build/debug/demos/ip_demo+0x46635d)
    #3 0x45b146 in sorter::get_next_temp_record(unsigned long) const (/home/onqtam/seastar/build/   debug/demos/ip_demo+0x45b146)
    #4 0x45b3fe in sorter::temp_cmp_functor::operator()(unsigned long, unsigned long) const (/home/ onqtam/seastar/build/debug/demos/ip_demo+0x45b3fe)
    #5 0x420298 in operator() ../../demos/ip_demo.cc:421

Answer 1

结果是整个类被复制到了某个地方，然后函数器对外部类的引用指向了旧的位置==>内存损坏。