c++ - bool 中的段错误

我正在尝试解决蛮力问题中的boogle问题。输入是：

网格矩阵，以字符串表示，例如：'pesa'
这个词，也表示为字符串“ asa”。

我正在编写一个函数来检查单词是否在矩阵中是合法单词。

bool Boogle::contains(std::string grid, std::string word) const
{
    bool* isvisited=new bool[grid.length()];
    for (unsigned int i=0; i<grid.length(); i++)
    {
        *(isvisited+i)=false;
    }

    for (unsigned int i=0; i<grid.length(); i++)
    {
        // Recursive approach
        if (grid[i]==word[0])
            if (checkqueue(grid, word, isvisited, i, 0))
                return true;
    }
    return false;
}

bool Boogle::checkqueue(const string &grid, const string &word, bool* const &isvisited, unsigned int grid_index, unsigned int count) const
{
    int matsize=int(sqrt(grid.length()));
    cout<<"\nCurrently at the index "<<grid_index<<"\n";
    isvisited[grid_index]=true;
    for (unsigned int i=0; i<grid.length(); i++)
    {
        cout <<isvisited[i]<<" ";
    }
    cout<<"\n";

    if (count==word.length()-1)
    {
        cout << " reach the end of word\n";
        return true;
    }
    else
    {
        count ++;
        cout << "Recursive call on WORD: "<<word<<"  " <<count<<" "<<word[count]<<"\n";

        // non diagonal
        if ((grid_index<grid.length()) && (isvisited[grid_index+1]==false) && (grid[grid_index+1]==word[count]))
            return checkqueue(grid, word, isvisited, grid_index+1, count);

        else if ((grid_index>0)&& (isvisited[grid_index-1]==false)  && (grid[grid_index-1]==word[count]))
            return checkqueue(grid, word, isvisited, grid_index-1, count);

        else if (((grid_index+matsize)<grid.length())&& (isvisited[grid_index+matsize]==false)  && (grid[grid_index+matsize]==word[count]))
            return checkqueue(grid, word, isvisited, grid_index+1, count);

        else if (((grid_index-matsize)<grid.length())&& (isvisited[grid_index-matsize]==false)  && (grid[grid_index-matsize]==word[count]))
            return checkqueue(grid, word, isvisited, grid_index+1, count);

        // diagonal
        else if ((grid_index-1-matsize>0)&& (isvisited[grid_index-1-matsize]==false)  && (grid[grid_index-1-matsize]==word[count]))
            return checkqueue(grid, word, isvisited, grid_index-1-matsize, count);

        else if ((grid_index+1-matsize>0) && (isvisited[grid_index+1-matsize]==false) && (grid[grid_index+1-matsize]==word[count]))
            return checkqueue(grid, word, isvisited, grid_index+1-matsize, count);

        else if ((grid_index+1+matsize<grid.length())&& (isvisited[grid_index+1+matsize]==false)  && (grid[grid_index+1+matsize]==word[count]))
            return checkqueue(grid, word, isvisited, grid_index+1+matsize, count);

        else if ((grid_index-1+matsize<grid.length())&& (isvisited[grid_index-1+matsize]==false)  && (grid[grid_index-1+matsize]==word[count]))
            return checkqueue(grid, word, isvisited, grid_index-1+matsize, count);
        else
        {
            // cout<<"No possible neighbor\n";
            return false;
        }

    }
}

如果我运行boogle.contains（“ pesa”，“ as”），效果很好。但是，如果这是非法单词（例如“ asa”），则会返回细分错误。那是哪里来的

./Boogle.exe
.
Currently at the index 3
0 0 0 1
Recursive call on WORD: asa  1 s

Currently at the index 2
0 0 1 1
Recursive call on WORD: asa  2 a
Segmentation fault: 11

P / S：单词有效时，这是正确的运行（boogle.contains（“ pesa”，“ esp”））

Currently at the index 1
0 1 0 0
Recursive call on WORD: esp  1 s

Currently at the index 2
0 1 1 0
Recursive call on WORD: esp  2 p

Currently at the index 3
0 1 1 1
 reach the end of word



OK (1 tests)

最佳答案

如果尝试在条件列表之前显示cout << grid_index-1-matsize << endl;。您将看到由于grid_index是无符号的，因此发生了缓冲区下溢。

因此，您将(grid_index-matsize)<grid.length()设置为true，因为grid_index超出了grid.length()。

您必须将函数checkqueue的签名更改为

bool Boogle::checkqueue(const string &grid, const string &word, bool* const &isvisited, int grid_index, unsigned int count) const