无法访问地址 0x4 （unordered_map） 处的内存

问：

我正在编写一个拼写检查器，它使用 Levenshtein Distance 算法和字典的哈希映射。此函数旨在将一个字符串作为输入，将其与整个字典进行比较，然后输出一个具有最小 lev 距离的字符串。

std::string SpellChecker::levenshteinDist(std::string word)
{
    std::string minDistStr;

    int minDist = INT_MAX;

    //convert to char[]
    char a[word.length()];
    
    strcpy(a, word.c_str());

    for(auto i: dictionary)
    {
        std::string bString = i.first;

        char b[i.first.length()];

        strcpy(b, i.first.c_str());
    
        int aLength = word.length();

        int bLength = i.first.length();

        int grid[aLength][bLength] = {};

        for(int col = 0; col < aLength + 1; col++){
            for(int row = 0; row < bLength + 1; row++){
                if(col == 0)
                {
                    //Initialize first column
                    grid[0][row] = row;
                }
                else if(row == 0)
                {
                    //initialize first row
                    grid[col][0] = col;
                }
                else if(a[col-1] == b[row-1])
                {
                    grid[col][row] = grid[col-1][row-1];
                }
                else
                {
                    //Find cost of each operation
                    int insert = grid[col-1][row];
                    int replace = grid[col-1][row-1];
                    int del = grid[col][row-1];

                    // Minimum operation is recorded
                    grid[col][row] = 1 + std::min(std::min(insert, replace), del);
                }
            }
        }

        if(grid[aLength][bLength] < minDist)
        {
            minDist = grid[aLength][bLength];
            minDistStr = bString;
        }
        
    }
    
    return minDistStr;
}

该函数适用于前几个字典项，但最终遇到异常，我的调试器不显示 bString 的值，而是显示 .下面是 SpellChecker 的类声明<error: Cannot access memory at address 0x4>

class SpellChecker{
    private:
        std::unordered_map<std::string, bool> dictionary;
    public:
        SpellChecker(std::string fileName);
        bool search(std::string word);
        std::vector<std::string> similarWords(std::string word);
        std::string levenshteinDist(std::string word);
};

SpellChecker::SpellChecker(std::string fileName)
{
    std::ifstream dictFile;
    dictFile.open(fileName);
    std::string pipeStr;

    while (dictFile)
    {
        dictFile >> pipeStr;
        dictionary[pipeStr] = true;
    }

}

词典是一个文本文件，其中包含由换行符分隔的单个单词。为什么会这样？