有关DownloadFireware,设置buf的情况

就是说.我这里首先要fireware从当前路径中down到buf中.并设置它.我就这一块出问题了.不知道也没关系.毕竟不一样的.网卡和别的卡不一样
该段代码是:
BOOLEAN CMB86390::DownLoadFirmware()
{
char buf, rbuf;
bool result;
int trytimes = 0;

/* load firmware at start-up : read from disk file */
{
/* using namespace std */
using std::ifstream;
ifstream in(\"firmware.hex\");
assure(in, \"firmware.hex\");

while (in.read(&buf, 1))
{
if (!isalnum(buf)) continue;//这句出现错误.

if (buf == 0xa || buf == 0xd)
continue;
....................

}
也就是说.当前buf中不是字符和数字.怎么办呢..??