在c中使用匹配精确词

问题描述

我可以使用strstr函数匹配确切的单词吗?例如，假设我有一个单词hello和一个输入字符串line:

Can I use the strstr function to match exact word? For example, let's say I have the word hello, and an input string line:

如果

char* line = "hellodarkness my old friend";

我用

result = strstr(line, "hello");

result将匹配(不是NULL)，但是我只想匹配精确的单词"hello"(这样"hellodarkness"将不匹配)，结果将为NULL.是否可以使用strstr来执行此操作，还是我必须使用fscan并逐字扫描行并检查是否匹配?

result will match (be not NULL), however I want to match only the exact word "hello" (so that "hellodarkness" would not match) and result will be NULL.Is it possible to do this using strstr or do I have to use fscan and scan the line word by word and check for matches?

推荐答案

我会:

• 检查字符串是否在句子中
• 如果在开始时找到(与line相同的指针)，则添加单词的长度并检查是否找到了字母数字字符.如果不是(或以空值结尾)，则匹配
• 如果在其他任何地方找到，请添加额外的之前没有字母数字"测试

• check if string is in sentence
• if found at start (same pointer as line), add the length of the word and check if alphanumerical char found. If not (or null-terminated), then match
• if found anywhere else, add the extra "no alphanum before" test

代码:

#include <stdio.h>
#include <strings.h>
#include <ctype.h>
int main()
{
  const char* line = "hellodarkness my old friend";
  const char *word_to_find = "hello";
  char* p = strstr(line,word_to_find);
  if ((p==line) || (p!=NULL && !isalnum((unsigned char)p[-1])))
  {
     p += strlen(word_to_find);
     if (!isalnum((unsigned char)*p))
     {
       printf("Match\n");
     }
  }
  return 0;
}

在这里它什么也不会打印，但是在"hello"之前/之后插入一个标点符号/空格，或者在"hello"之后终止该字符串，您将得到一个匹配项.另外，您将无法通过在之前插入字母数字字符打招呼.

here it doesn't print anything, but insert a punctuation/space before/after or terminate the string after "hello" and you'll get a match. Also, you won't get a match by inserting alphanum chars before hello.

只有1个"hello"时，上面的代码很好，但是在"hellohello hello"中找不到第二个"hello".因此，我们必须插入一个循环来查找单词或NULL，每次都使p前进，如下所示:

the above code is nice when there's only 1 "hello" but fails to find the second "hello" in "hellohello hello". So we have to insert a loop to look for the word or NULL, advancing p each time, like this:

#include <stdio.h>
#include <strings.h>
#include <ctype.h>
int main()
{
  const char* line = "  hellohello hello darkness my old friend";
  const char *word_to_find = "hello";
  const char* p = line;

  for(;;)
  {
    p = strstr(p,word_to_find);
    if (p == NULL) break;

    if ((p==line) || !isalnum((unsigned char)p[-1]))
    {
       p += strlen(word_to_find);
       if (!isalnum((unsigned char)*p))
       {
         printf("Match\n");
         break;  // found, quit
       }
    }
    // substring was found, but no word match, move by 1 char and retry
    p+=1;
  }

  return 0;
}

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