std :: vector <bool> resize（）的未定义行为

Question

#include <vector>
int main()
{
    try {
        std::vector<bool> a;
        a.resize(a.max_size() - 100000000);
    }
    catch (...) {
        return -1;
    }
    return 0;
}

I tried to run this program with VS2015 x86, but it crashed in resize() with "Access violation". I wonder if there is any undefined behavior? What does the C++ standard say about this?

Answer 1

vector<bool> doesn't always behave like a vector, and it never actually stores bools, but a packed representation of bools that is designed to save space(bitfields). vector<bool> doesn't satisfy the requirements of an STL container, you're best off not using it. deque<bool> and bitset are alternatives data structures that will almost certainly satisfy your need for the capabilities promised by vector<bool> .