/* 显示程序的使用方法 */
void help()
{
printf("Usage : list specified files and several characters in the head of file\n");
printf("Syntex : XDIR <filename or directory> <number of ASCII characters>\n");
printf("Example: XDIR *.C 30\n");
printf(" XDIR *.*\n");
}
/* 显示错误信息 */
void error()
{
printf("Error : File not found !!!\n");
help();
exit(0);
}