如何使strcasecmp在不区分大小写的情况下比较字符串

Question

我正在用C语言编写一个cs50在线课程，我的项目是编写一个函数，将字典(单词数据库)加载到内存中，将其有效地散列到哈希表中，然后比较给定文本中的单词以检查拼写，它必须进行比较而不区分大小写。

在这个概述中，我遇到的主要问题是降低对大小写的敏感性，因此我不确定下面的strcasecmp函数是如何出错的。我知道内存泄漏，但是稍后会解决它们。

下面是C中的代码：

    //for the universal hash function
    #define BASE 256
    
    // Represents a node in a hash table
    typedef struct node
    {
        char word[LENGTH + 1];
        struct node *next;
    }
    node;
    
    // Number of buckets in hash table
    const unsigned int N = 676;
    
    // Hash table
    node *table[N];
    int word_count = 0;
    
    // Returns true if word is in dictionary else false
    //Require a search funtion
    bool check(const char *word)
    {
        int hashIndex = hash(word);
        for (node *tmp = table[hashIndex]; tmp != NULL; tmp = tmp->next)
        {
            
            if (strcasecmp(word, tmp->word) == 0)
            {
                return true;
            }
        }
        return false;
    }
    
    // Hashes word to a number
    // the dividing hash function is one I cited from the yale.edu page http://www.cs.yale.edu/homes/aspnes/pinewiki/C(2f)HashTables.html having worked with.
    unsigned int hash(const char *word)
    {
        unsigned long m = 11;
        unsigned long h;
        unsigned const char *us;
        //ensure element value is >= 0 
        us = (unsigned const char *) word;
      
        h = 0;
        while(*us != '\0') 
        {
            h = (h * BASE + *us) % m;
            us++;
        } 
        return (h % N);
    }

当使用由check50提供的CS50函数进行检查时，我得到：

> :( spell-checking is case-insensitive expected "MISSPELLED WOR...",
> not "MISSPELLED WOR..." Log running ./speller case/dict case/text...
> checking for output "MISSPELLED WORDS\n\n\nWORDS MISSPELLED: 0\nWORDS
> IN DICTIONARY: 1\nWORDS IN TEXT: 8\n"...
> 
> Expected Output: MISSPELLED WORDS
> 
> 
> WORDS MISSPELLED:     0 WORDS IN DICTIONARY:  1 WORDS IN TEXT:       
> 8 Actual Output: MISSPELLED WORDS
> 
> foO fOo Foo fOO FoO FOo FOO
> 
> WORDS MISSPELLED:     7 WORDS IN DICTIONARY:  1 WORDS IN TEXT:       
> 8
> 
> :( handles most basic words properly expected "MISSPELLED WOR...", not
> "MISSPELLED WOR..." Log running ./speller basic/dict basic/text...
> checking for output "MISSPELLED WORDS\n\n\nWORDS MISSPELLED: 0\nWORDS
> IN DICTIONARY: 8\nWORDS IN TEXT: 9\n"...
> 
> Expected Output: MISSPELLED WORDS
> 
> 
> WORDS MISSPELLED:     0 WORDS IN DICTIONARY:  8 WORDS IN TEXT:       
> 9 Actual Output: MISSPELLED WORDS
> 
> The
> 
> WORDS MISSPELLED:     1 WORDS IN DICTIONARY:  8 WORDS IN TEXT:       
> 9

主要的问题是:我如何才能不区分大小写，来比较两个字符串呢？

Answer 1

这个if (strcasecmp(word, tmp->word) == 0)并不是单词大小写有意义的唯一地方。那hash呢？它还需要考虑字母大小写，例如'a‘和'A’将散列成不同的值。