收集c语言常用函数

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收集c语言常用函数

Table of Contents

• 1 概
• 2 strcasecmp()
  • 2.1 算法：
  • 2.2 代码：

1 概

在平时的开发中有时候会写一些很有趣的函数，所以在这时记录一下。

2 strcasecmp()

2.1 算法：

很简单，先将其转为小写，再进行统一比较。

2.2 代码：

     /* Compare S1 and S2, ignoring case, returning less than, equal to or
       greater than zero if S1 is lexicographically less than,
       equal to or greater than S2.  */
    int
    strcasecmp (const char *s1, const char *s2)
    {
      register const unsigned char *p1 = (const unsigned char *) s1;
      register const unsigned char *p2 = (const unsigned char *) s2;
      unsigned char c1, c2;

      if (p1 == p2)
        return 0;

      do
        {
          c1 = tolower (*p1++);
          c2 = tolower (*p2++);
          if (c1 == '\0')
            break;
        }
      while (c1 == c2);

      return c1 - c2;
    }


    

另外一个strncasecmp():

/* Compare no more than N characters of S1 and S2,
   ignoring case, returning less than, equal to or
   greater than zero if S1 is lexicographically less
   than, equal to or greater than S2.  */
int
strncasecmp (const char *s1, const char *s2, size_t n)
{
  register const unsigned char *p1 = (const unsigned char *) s1;
  register const unsigned char *p2 = (const unsigned char *) s2;
  unsigned char c1, c2;

  if (p1 == p2 || n == 0)
    return 0;

  do
    {
      c1 = tolower (*p1++);
      c2 = tolower (*p2++);
      if (c1 == '\0' || c1 != c2)
        return c1 - c2;
    } while (--n > 0);

  return c1 - c2;
}

Date: 2013-01-16 WED

Author: liweilijie

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