收集c语言常用函数
Table of Contents
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;
}