error in STL sort function with Compare function - c++

Question

i try to sort a vector which element-type is a class like following:
void sort_test() {
class A{
public:
A(float x, float y, float z):score_(x),rerank_score_(y),ranking_score_(z) {};
float score_;
float rerank_score_;
float ranking_score_;
};
using A_ptr = std::shared_ptr<A>;
auto CompareA_ptr = [](A_ptr x, A_ptr y) {
if (x == nullptr && y != nullptr) {
return false;
} else if (x == nullptr && y == nullptr) {
return false;
} else if (x != nullptr && y == nullptr) {
return true;
} else {
if (x->rerank_score_ > y->rerank_score_) {
return true;
} else if (x->rerank_score_ < y->rerank_score_) {
return false;
} else {
if (x->score_ > y->score_) {
return true;
} else if (x->score_ < y->score_) {
return false;
} else {
return x->ranking_score_ >= y->ranking_score_;
}
}
}
};
std::vector<A_ptr> X;
for (int i = 0; i < 7; ++i) {
X.push_back(std::make_shared<A>(A(0.1, 0.1, 0.1)));
}
std::sort(X.begin(), X.end(), CompareA_ptr);
}
int main(){
sort_test();
return 0;
}
I run the code in Xcode and get the Xcode error "Thread 1: EXC_BAD_ACCESS (code=EXC_I386_GPFLT)"in memory.cpp:
I found that the code runs correctly when the vector size is less than 7, and an error is reported when the vector size is greater than 7. It bothers me a lot.
Appreciate for any reply.

Answer 1

Testing your code in Visual Studio revelas that CompareA_ptr doesn't define a strict weak ordering as required for a comparator. This causes undefined behaviour.
The culprit seems to be
return x->ranking_score_ >= y->ranking_score_;
where >= should be changed to >
return x->ranking_score_ > y->ranking_score_;