C ++ STL堆栈弹出操作给出分段错误 [英] C++ STL stack pop operation giving segmentation fault

问题描述

我从 this link 在 C++ 中实现了一个编程问题，但我得到了一个我的代码在 pop() 操作中出现分段错误.我对 C++ 还很陌生，自己似乎找不到错误.

I implemented a programming question from this link in C++ but I am getting a segmentation fault in the pop() operation with my code. I am fairly new to C++ and can not seem to find the error myself.

#include<iostream>
#include<stack>

using namespace std;

void printNge(int *arr);

int main() {
        int arr[] = {1,4,2,6,3,8,7,2,6};

        printNge(arr);

        return 0;
}

void printNge(int *arr) {
        stack<int> st;

        st.push(arr[0]);

        for(int i=1; i<9;i++) {
                while((st.top() < arr[i]) && (!st.empty())) {
                        cout << "Element is:" << st.top() << "  NGE is:" << arr[i] << endl;
                        cout << "Removing element: " << st.top() << endl;
                        st.pop();
                }
                cout << "Pushing element: " << arr[i] << endl;
                st.push(arr[i]);
        }
        while(!st.empty()) {
                cout << "Element is:" << st.top() << "  NGE is:" << -1 << endl;
                st.pop();
        }

}

感谢您的帮助.

推荐答案

这一行

while((st.top() < arr[i]) && (!st.empty())) {

是导致段错误的原因.在尝试访问顶部之前，您必须检查堆栈是否为空，因为在空堆栈上调用 top 会调用 UB.

is what is causing the segfault. You have to check the stack for being empty before you try to access top, as caling top on empty stack invokes UB.

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