Question

我的程序存在这个小问题。在Visual Studio 2012中，它运行正常，但如果我用G ++编译它（是的，由于我上面的原因，我必须用它来编译），错误信号11（SIGSEGV）或6（SIGABRT）根据输入被触发。这是一个编程练习，我有另一个程序（在一个在线服务器上），用10个不同的输入测试我的程序。正如我所说，该程序在使用Visual Studio 2012时编译并运行良好。

关于该计划：它找到从起点（x，y）到多个出口的最短路径（出口量不相关且不同。可能只有1个出口或者可能有200个出口）。输入如下：

7 12          // maze height and width
##########.#  //
#..........#  //
#.###.######  //
#..X#.#.....  // the maze blueprint
#.###.#.####  //
#..........#  //
############  //

我的节目：

#include <iostream>
#include <vector>

typedef struct _laby_t {
    int h, w;
    char **pohja; // 'pohja' is finnish and means layout
} laby_t;

typedef std::vector<int> monovector;
typedef std::vector< std::vector<int> > bivector;

laby_t *laby_allocate (int r, int c)
{
    laby_t *laby;
    int i;

    laby = new laby_t[sizeof (laby_t)];
    laby->pohja = new char *[r];
    for (i = 0; i < r; i++)
    {
        laby->pohja[i] = new char[c];
    }
    laby->h = r;
    laby->w = c;

    return laby;
}

int wander(int y, int x, laby_t *&_laby, int goals)
{
    laby_t *laby = _laby;
    int found = 0, depth = 0, min_path = 1000000;
    bool b = 0;
    bivector openList;
    monovector start; start.push_back(y); start.push_back(x);
    bivector closedList;

    openList.push_back(start);

    while(found < goals)
    {

        y = openList.back()[0]; x = openList.back()[1];
        monovector r; r.push_back(y); r.push_back(x); closedList.push_back(r);
        openList.pop_back();
        if(laby->pohja[y][x] != '*') laby->pohja[y][x] = '-';
        depth++;

        if(y == 0 || y+1 == laby->h || x == 0 || x+1 == laby->w) {
            found++;
            if(depth < min_path) min_path = depth;
            if(found >= goals) {
                std::cout << min_path << std::endl;
                break;
            }
            laby->pohja[y][x] = '-';

            goto back_track;
        }
        else
        {
            b = 0;
            if(laby->pohja[y+1][x  ] == '.') { monovector r; r.push_back(y+1); r.push_back(x); openList.push_back(r); b=1; }
            if(laby->pohja[y  ][x+1] == '.') { monovector r; r.push_back(y); r.push_back(x+1); openList.push_back(r); b=1; }
            if(laby->pohja[y-1][x  ] == '.') { monovector r; r.push_back(y-1); r.push_back(x); openList.push_back(r); b=1; }
            if(laby->pohja[y  ][x-1] == '.') { monovector r; r.push_back(y); r.push_back(x-1); openList.push_back(r); b=1; }
            if(!b)
            {
back_track:     while(closedList.size() > 0)
                {
                    //std::cout << closedList.size() << std::endl;
                    int c_y = closedList.back()[0]; int c_x = closedList.back()[1];
                    int o_y = openList.back()[0];   int o_x = openList.back()[1];

                    laby->pohja[y][x] = '*';

                    y = c_y; x = c_x;

                    laby->pohja[y][x] = '*';

                    if( (c_y+1 == o_y && c_x   == o_x) ||
                        (c_y   == o_y && c_x+1 == o_x) ||
                        (c_y-1 == o_y && c_x   == o_x) ||
                        (c_y   == o_y && c_x-1 == o_x) )
                    {
                        laby->pohja[y][x] = '-';
                        y = o_y; x = o_x;
                        closedList.pop_back();
                        depth--;
                        break;
                    }
                    else {
                        closedList.pop_back();
                        depth--;
                    }
                }
            }
        }
    }

    return min_path;
}

int main()
{
    int h, w, goals = 0;
    std::cin >> h >> w;

    laby_t *laby;
    laby = laby_allocate(h, w);

    for(int i = 0; i < laby->h; i++)
        std::cin >> laby->pohja[i];

    for(int i = 1; i < laby->h-1; i++) {
        if(laby->pohja[i][0] == '.') goals++;
        if(laby->pohja[i][laby->w-1] == '.') goals++;
    }

    for(int i = 1; i < laby->w-1; i++) {
        if(laby->pohja[0][i] == '.') goals++;
        if(laby->pohja[laby->h-1][i] == '.') goals++;
    }

    for(int i = 0; i < laby->h; i++)
        for(int j = 0; j < laby->w; j++) {
            if(laby->pohja[i][j] == 'X') {
                wander(i, j, laby, goals);
                goto _exit;
            }
        }

_exit:

    //system("pause");
    return 0;
}

我已完成关于错误信号的作业，如果你们不知道的话：http://www.yolinux.com/TUTORIALS/C++Signals.html

提前致谢。

Answer 1

代码使用G ++ 4.7.1在Mac OS X 10.7.5上干净地编译，这很好：

g++ -g -Wall -Wextra laby.cpp -o laby

不幸的是，当结果在valgrind下运行时，它会产生：

==15030== Invalid write of size 1
==15030==    at 0x306BE: std::basic_istream<char, std::char_traits<char> >& std::operator>><char, std::char_traits<char> >(std::basic_istream<char, std::char_traits<char> >&, char*) (in /usr/lib/libstdc++.6.0.9.dylib)
==15030==    by 0x10000117D: main (laby.cpp:113)
==15030==  Address 0x10001632c is 0 bytes after a block of size 12 alloc'd
==15030==    at 0xB823: malloc (vg_replace_malloc.c:266)
==15030==    by 0x5768D: operator new(unsigned long) (in /usr/lib/libstdc++.6.0.9.dylib)
==15030==    by 0x576DA: operator new[](unsigned long) (in /usr/lib/libstdc++.6.0.9.dylib)
==15030==    by 0x1000008C0: laby_allocate(int, int) (laby.cpp:21)
==15030==    by 0x100001146: main (laby.cpp:110)

因此，laby_allocate()函数中的内存分配存在问题。或者几个......

laby_t *laby_allocate (int r, int c)
{
    laby_t *laby;
    int i;

    laby = new laby_t[sizeof (laby_t)];

此行分配laby_t的数组;它在数组中分配与laby_t中的字节数一样多的元素。这不是你需要的。

    laby = new laby_t;

继续：

    laby->pohja = new char *[r];
    for (i = 0; i < r; i++)
    {
        laby->pohja[i] = new char[c];
    }

这没有为数据末尾的空值分配足够的空间......这就是'write'为1个字节的原因。将c更改为c+1，valgrind可以提供清晰的健康状况。

    laby->h = r;
    laby->w = c;

    return laby;
}

答案是15;我不相信这是正确的。

Answer 2

此行溢出了内存分配。如果用户输入 w 字符，则需要（w + 1）字符来保存以空字符结尾的字符串。

    std::cin >> laby->pohja[i];

这一行也分配了许多laby_t个对象的数组，尽管你似乎只想要一个。也许你把C ++ new与C malloc混淆了。

laby = new laby_t[sizeof (laby_t)];

你可以用它替换它。

laby = new laby_t;

这似乎也是C的残余。它不是一个bug，但是它会用reduntant符号不必要地污染当前的命名空间。

typedef struct _laby_t { ... } laby_t;

你可以用它替换它。

struct laby_t { ... };

被信号11（SIGSEGV）和/或6（SIGABRT）杀死

2 个答案: