Question

当我调试时，程序在subset()的第3行崩溃。运行程序和调试有两张图片......

#include <iostream>
#include <cmath>
#include <cstdio>
#include <stack>
using namespace std;

int c[6];
char s[101];
int end, yes;
stack<char> sstk;
stack<int> nstk;

int toInt(char ch)
{
    int temp;
    switch(ch)
    {
        case 'p':   temp = c[0];
            break;
        case 'q':   temp = c[1];
            break;
        case 'r':   temp = c[2];
            break;
        case 's':   temp = c[3];
            break;
        case 't':   temp = c[4];
            break;
        default:
            cout<<"Char incorrect :"<<endl;
    }
    return temp;
}

int oper(int x, int y, char ch)
{
    switch(ch)
    {
        case 'K':
            if(1 == x && 1 == y)
                return 1;
            else
                return 0;
        case 'A':
            if(0 == x && 0 == y)
                return 0;
            else
                return 1;
        case 'C':
            if(1 == x && 0 == y)
                return 0;
            else
                return 1;
        case 'E':
            if(x == y)
                return 1;
            else
                return 0;
        default:
            cout<<"Operation error"<<endl;
            return -1;
    }
}

bool isOper(char ch)
{
    switch(ch)
    {
        case 'K': case 'A': case 'N': case 'C': case 'E':
            return true;
        default:
            return false;
    }
}

int isTau()
{
    char a, b, p, t;
    int f;                      //f==1 means the char was asigned
    p = s[0];             cout<<"A time p="<<p<<endl;
    if(p == 0)
        return -1;
    if(!isOper(p) )
        return 0;
    int i = 1;
    while((t=s[i++]) != '!')
    {   cout<<t<<endl;
        if(isOper(t) )          //If the t char is operator, push previous opertator
        {
            if(1 == f)          //and push the a operand if there is one
                nstk.push(a);
            sstk.push(p);
            p = t;              //replace the p with t
            f = 0;
            continue;
        }

        int num = toInt(t);     //If t is not operatand, trans it to int
        if(p == 'N')            //To operate either there is an N or f==1(a, b, p)
        {
            b = (num == 1 ? 0 : 1);
        }
        if(1 == f)
        {
            b = oper(a, num, p);
        }
        else
        {
            a = num;
            f = 1;
            continue;
        }

        while(!sstk.empty() )
        {
            p = sstk.top();
            if('N' == p)
            {
                b = (b == 1 ? 0 : 1);
                sstk.pop();
                continue;
            }
            a = nstk.top();
            b = oper(a, b, p);
            nstk.pop();
            sstk.pop();
        }

        a = b;
        f = 0;
    }
    if(1 == a)
        return 1;
    else
        return 0;
}

void subset(int n,int *A, int cur)
{
    for(int i=0; i<cur; i++)
    {   cout<<A[i]<<" ";
        c[A[i]] = 1;
    }   cout<<endl;
    if(cur != 0)
    {
        int t = isTau();    //cout<<"Is Tas: "<<t<<endl;
        if(t == -1)
        {
            end = 1;
            return;
        }
        if(t == 0)
            yes = 0;
    }
    int s = cur ? A[cur-1]+1 : 0;
    for(int i=s; i<n; i++)
    {
        A[cur] = i;
        subset(n, A, cur+1);
        if(end == 1)
            return;
    }
}

int main()
{
    freopen("input.txt","r",stdin);
    do
    {   cout<<"Loop : "<<endl;
        int i;
        char t;
        for(i=0; (t=getchar() ) != '\n'; i++)
        {
            s[i] = t;
        }
        s[i] = '!';
        int *a;
        subset(5,a,0);  cout<<"what?";
        if(yes == 1)
            cout<<"tautology"<<endl;
        else
            cout<<"not"<<endl;
    }while(end == 0);

    return 0;
}

Running

Call stack

Answer 1

int *a;
subset(5,a,0);  cout<<"what?";

此处a被定义为指向整数的指针，但从未初始化。然后传递给subset，试图取消引用它......

cout<<A[i]<<" ";

...导致UB（未定义的行为）。从那里发生的一切，包括崩溃，都是UB的可能结果。

您可以在使用之前将a指向已分配的缓冲区：

int *a = new int[5]; // uninitialized, use instead 'new int[5]();' to initialize to all-0
subset(5,a,0);  cout<<"what?";
// ...
// remember to 'delete [] a;' when no longer used

或者您可以将a更改为本地数组：

int a[5]; // uninitialized, use instead 'int a[5] = { 0 };` to initialize to all-0
subset(5,a,0);  cout<<"what?";

为什么我的程序终止调用KERNEL32！FileTimeToSystemTime（）？

1 个答案: