C 去除 字符串两边的空字符

今天在一国外网站上, 看到下面的代码, 觉得挺精简. 

char *tr ( char *s )
{
  int i = 0;
  int j = strlen ( s ) - 1;
  int k = 0;
 
  while ( isspace ( s[i] ) && s[i] != '\0' )
    i++;
 
  while ( isspace ( s[j] ) && j >= 0 )
    j--;
 
  while ( i <= j )
    s[k++] = s[i++];
 
  s[k] = '\0';
 
  return s;
}