c++ - 我的程序在 openSUSE 中出现段错误

Question

我有一台笔记本电脑，一个月前安装了 openSUSE 13.2。当我尝试运行此 C++ 程序来打印最短路径时，出现段错误。另一方面，我的代码在安装了 Ubuntu 的计算机上完美运行。

这是我在 Ubuntu 中得到的输出...

rohan@Symantha:~/Dropbox/cprog/Arrayss/2D$ uname -a
Linux Symantha 3.13.0-53-generic #89-Ubuntu SMP Wed May 20 10:34:28 UTC 2015 i686 i686 i686 GNU/Linux
rohan@Symantha:~/Dropbox/cprog/Arrayss/2D$ g++ 16.cpp 
rohan@Symantha:~/Dropbox/cprog/Arrayss/2D$ ./a.out 
Enter total rows : 4
Enter total cols : 4
Enter array ->
1 0 0 0
1 1 1 0
0 1 1 0
1 1 1 1
Input Ok ..
Enter source row: 0
Enter source col: 0
Enter destination row: 3
Enter destination col: 3
Shortest Path -->>
path :  (0, 0) ->  (1, 0) ->  (1, 1) ->  (1, 2) ->  (2, 2) ->  (3, 2) ->  (3, 3) 

但是在 openSUSE 中，我得到了这个...

rohan@linux-zdor:~/Dropbox/cprog/Arrayss/2D> uname -a
Linux linux-zdor.site 3.16.7-21-desktop #1 SMP PREEMPT Tue Apr 14 07:11:37 UTC 2015 (93c1539) x86_64 x86_64 x86_64 GNU/Linux
rohan@linux-zdor:~/Dropbox/cprog/Arrayss/2D> g++ 16.cpp 
rohan@linux-zdor:~/Dropbox/cprog/Arrayss/2D> ./a.out 
Enter total rows : 4
Enter total cols : 4
Enter array ->
1 0 0 0
1 1 1 0
0 1 1 0
1 1 1 1
Input Ok ..
Enter source row: 0
Enter source col: 0
Enter destination row: 3
Enter destination col: 3
Shortest Path -->>
Segmentation fault

谁能告诉我我的代码有什么问题吗？这是我的代码:

https://drive.google.com/file/d/0BzLbrlYg9GyXd3E4WnFWc3lGVUk/view?usp=sharing

#include <iostream>
#include <unistd.h>
using namespace std;

#define MAXROW 10
#define MAXCOL 10

class Cell {
public:
  int row;
  int col;
  Cell() { }
  Cell(int rr, int cc) : row(rr), col(cc) { }
  bool operator==(const Cell& cc) {
    if(row == cc.row && col == cc.col)
      return true;
    else 
      return false;
  }
};

class Path {
  int row[MAXROW*MAXROW];
  int col[MAXCOL*MAXCOL];
  int size;
public:
  Path() : size(0) { }
  Path(Path& pp) {
    size = pp.size;
    for(int i = 0; i < size; i++) {
      row[i] = pp.row[i];
      col[i] = pp.col[i];
    }
  }
  Path& operator=(const Path& pp) {
    size = pp.size;
    for(int i = 0; i < size; i++) {
      row[i] = pp.row[i];
      col[i] = pp.col[i];
    }
  }
  int length() {
    return size;
  }
  void setSize(int ss) {
    size = ss;
  }
  void insert(int rr, int cc) {
    row[size] = rr;
    col[size] = cc;
    size++;
  }
  void print() {
    int i = 0;
    cout << "path : ";
    while(i < size) {
      cout << " (" << row[i] << ", "
           << col[i] << ") ";
      if(i < size-1)
        cout << "-> ";
      i++;
    }
    cout << endl;
  }
  bool searchCell(Cell c) {
    int i = 0;
    while(i < size) {  
      if(row[i] == c.row && col[i] == c.col)
        return true;
      i++;
    }
    return false;
  }
  Cell start() {
    return Cell(row[0], col[0]);
  }
  Cell end() {
    if(size > 0)
      return Cell(row[size-1], col[size-1]);
    else
      return Cell(-1, -1);
  }
};


Path shortestPath(int arr[][MAXCOL], int, int, Cell, Cell, Path);
void inputArr(int arr[][MAXCOL], int mR, int mC);


int main() {
  int arr[10][10], mR, mC, r, c;
  Path p;
  cout << "Enter total rows : ";
  cin >> mR;
  cout << "Enter total cols : ";
  cin >> mC;
  cout << "Enter array ->\n";
  inputArr(arr, mR, mC);
  cout << "Input Ok ..\n";
  cout << "Enter source row: ";
  cin >> r;
  cout << "Enter source col: ";
  cin >> c;
  Cell source(r, c);
  cout << "Enter destination row: ";
  cin >> r;
  cout << "Enter destination col: ";
  cin >> c;
  Cell destination(r, c);
  cout << "Shortest Path -->>\n";
  p = shortestPath(arr, mR, mC, source, destination, p);  
  p.print();
  return 0;
}

Path shortestPath(int arr[][MAXCOL], int mR, int mC, Cell current, Cell target, Path p) {
  int i = current.row;
  int j = current.col;
  Path p_array[4];
  if(arr[i][j] == 0 || i == mR || j == mC || i < 0 || j < 0 
     || p.searchCell(current)) {
    p.setSize(0);
    return p;
  }
  p.insert(i, j);
  if(i == target.row  &&  j == target.col) 
    return p;  
  else {
    // Since there are four possible directions
    p_array[0] = shortestPath(arr, mR, mC, Cell(i, j+1), target, p);
    p_array[1] = shortestPath(arr, mR, mC, Cell(i+1, j), target, p);
    p_array[2] = shortestPath(arr, mR, mC, Cell(i, j-1), target, p);
    p_array[3] = shortestPath(arr, mR, mC, Cell(i-1, j), target, p);
    int minIndex, minSize, i;
    for(i = 0; i < 4; i++) {
      if(p_array[i].length() != 0 && p_array[i].end() == target ) {
        minIndex = i;
        minSize = p_array[i].length();
        break;
      }
    }    
    for(i = 0; i < 4; i++) {
      if(p_array[i].length() < minSize && p_array[i].end() == target) {
        minIndex = i;
        minSize = p_array[i].length();
      }
    }
    return p_array[minIndex];
  }
}

void inputArr(int arr[][MAXCOL], int mR, int mC) {
  int i, j;
  for(i = 0; i < mR; i++)
    for(j = 0; j < mC; j++)
      cin >> arr[i][j];
}

Answer 1

您的 shortestPath 函数中的验证顺序错误:

if (arr[i][j] == 0 || i == mR || j == mC || i < 0 || j < 0 
    || p.searchCell(current)) {

在检查边界是否有效之前，您访问了数组越界。这是未定义的行为，并且不同的系统在存在未定义的行为时可能表现不同(因此崩溃和看似工作都是对调用未定义行为的有效响应)。

在访问数组之前重写条件以检查索引是否正确。

if (i == mR || j == mC || i < 0 || j < 0 || arr[i][j] == 0
    || p.searchCell(current)) {

这可能不是唯一的问题；这是一个问题。

<小时/>

当我从问题中逐字获取代码并编译它时，我收到编译警告(因为我使用 -Werror 将警告转换为错误，所以出现错误)。

$ g++ -O3 -g -std=c++11 -Wall -Wextra -Werror 16.cpp -o 16
16.cpp: In member function ‘Path& Path::operator=(const Path&)’:
16.cpp:41:3: error: no return statement in function returning non-void [-Werror=return-type]
   }
   ^
16.cpp: In function ‘Path shortestPath(int (*)[10], int, int, Cell, Cell, Path)’:
16.cpp:143:40: error: ‘minSize’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
       if(p_array[i].length() < minSize && p_array[i].end() == target) {
                                        ^
16.cpp:29:15: error: ‘minIndex’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
     size = pp.size;
               ^
16.cpp:134:9: note: ‘minIndex’ was declared here
     int minIndex, minSize, i;
         ^
cc1plus: all warnings being treated as errors
$

这些都是严重的问题，可能会导致您的代码失控。当然，您需要先解决这些问题，然后才值得做其他事情。

我注意到你有:

class Path {
    int row[MAXROW*MAXROW];
    int col[MAXCOL*MAXCOL];

目前，MAXROW == MAXCOL，因此 row 和 col 中的元素数量相同，但如果数字不同，您可能无法将路径的所有成员存储在两个数组的一个或另一个中。不太好。数组的大小应无条件相同。另外，在 main() 中，您定义:

 int arr[10][10], …

当然应该是:

int arr[MAXROW][MAXCOL], …

使用最少的修正，在 shortestPath() 中设置 minIndex = -1 和 minSize = -1，并将 return *this; 添加到赋值运算符，然后在 shortestPath() 末尾添加诊断打印:

Path shortestPath(int arr[][MAXCOL], int mR, int mC, Cell current, Cell target, Path p) {
  int i = current.row;
  int j = current.col;
  Path p_array[4];
  cerr << "-->> shortestPath(" << i << "," << j << ")\n";
  //if(arr[i][j] == 0 || i == mR || j == mC || i < 0 || j < 0
  if (i == mR || j == mC || i < 0 || j < 0 || arr[i][j] == 0 || p.searchCell(current)) {
    p.setSize(0);
    cerr << "<<-- shortestPath() - 1\n";
    return p;
  }
  p.insert(i, j);
  if (i == target.row && j == target.col)
  {
    cerr << "<<-- shortestPath() - 2\n";
    return p;
  }
  else {
    // Since there are four possible directions
    p_array[0] = shortestPath(arr, mR, mC, Cell(i, j+1), target, p);
    p_array[1] = shortestPath(arr, mR, mC, Cell(i+1, j), target, p);
    p_array[2] = shortestPath(arr, mR, mC, Cell(i, j-1), target, p);
    p_array[3] = shortestPath(arr, mR, mC, Cell(i-1, j), target, p);
    int minIndex = -1, minSize = -1, i;
    for(i = 0; i < 4; i++) {
      if(p_array[i].length() != 0 && p_array[i].end() == target ) {
        minIndex = i;
        minSize = p_array[i].length();
        cerr << "1: minIndex: " << minIndex << ", minSize: " << minSize << "\n";
        break;
      }
    }
    for(i = 0; i < 4; i++) {
      if(p_array[i].length() < minSize && p_array[i].end() == target) {
        minIndex = i;
        minSize = p_array[i].length();
        cerr << "2: minIndex: " << minIndex << ", minSize: " << minSize << "\n";
      }
    }
    cerr << "3: minIndex: " << minIndex << "\n";
    cerr << "<<-- shortestPath() - 3\n";
    return p_array[minIndex];
  }
}

并运行它，部分输出为:

-->> shortestPath(2,0)
<<-- shortestPath() - 1
3: minIndex: -1
<<-- shortestPath() - 3

糟糕:访问和返回 p_array[-1] 不是一个好主意。你的下标失去了控制——难怪事情会变得困惑。您需要思考代码是否将 minIndex 设置为 -1 以外的值以及如何处理它。