另外stoi和exit（0）都在stk.cpp中超出范围，我不知道为什么。

这是main.cpp

#include "stk.h"

int main()
{
    cout << "REDACTED\n" << endl;
    stk m;
    m.startProg();

}

使用g++ -v main.cpp -o test as 编译时会导致此错误：

undefined reference to 'stk::startProg()'
collect2: error: ld returned 1 exit status

这是stk.h

#ifndef STK_H
#define STK_H

#include <iostream>
#include <string>
#include "stdio.h"

using namespace std;


class stk
{
    struct node
    {
        int data;
        node * next;
    };
    node *head;

    public:
        stk()
        {
            head = NULL;
        }
        int push(int val);
        int pop();
        int display();
        int reverse(node * temp);
        void insertAtBottom(int tVal, node * temp);
        bool isEmpty();
        int startProg();
    private:
};

#endif

这是stk.cpp中的startProg函数

    int stk::startProg()
 {
    while (true)
    {
        string line = "\0";
        getline(cin, line);

        if (0 == line.compare(0,4, "push"))
        {
            int val = 0;
            val = stoi(line.substr(5));
            push(val);
        }
        else if(0 == line.compare (0,3, "pop"))
        {
            pop();
        }
        else if (0 == line.compare(0,7, "isempty"))
        {
            printf ("%s\n", isEmpty() ? "true" : "false");
        }
        else if (0 == line.compare(0,7, "reverse"))
        {
            node * top = NULL;
            reverse(top);

        }
        else if (0 == line.compare(0,7, "display"))
        {
            display();
        }
        else if (0 == line.compare(0,4, "quit"))
        {
            exit(0);
        }

格式化失败，我假设所有括号都正确。