分段错误：C ++使用Lambda比较器对字符串向量进行排序

Question

int main() {
    vector<string> v(100, "0");
    auto comp = [](const string& first, const string& second)->bool {
        return first.compare(second) <= 0;
    };
    sort(v.begin(), v.end(), comp);
    for(auto s : v) {
        cout<<s<<endl;
    }
    return 0;
} 

Above c++ code got segmentation fault with g++ v4.9.2. it's so wired. who know what's going on?

Answer 1

Your comparison function is not a valid. It fails both at irreflexivity ( comp(x, x) should never be true ) and asymmetry ( if comp(x, y) is true, then comp(y, x) must be false ), both of which are part of the strict weak ordering which std::sort requires for its comparator. operator< or operator> satisfy this requirement. But operator<= and operator>= do not.

If you change your comparison function to this:

auto comp = [](const string& first, const string& second)->bool {
    return first.compare(second) < 0;
};

It will work. Of course, that is functionally identical to what you get as the default, so you could just do this:

sort(v.begin(), v.end());