linux下串口编程的一个怪问题，高手们看看。

Question

我在linux编写了两段最简单的串口收发程序。
其中如果发写成：write(fd,"abdce",;
收写成：read（fd,buff,5）;时能收到。
可是我想将write改为write(fd,buf,;时，其中之前已经赋值buf="abcde"收端却没反应。百思不得其解，还请高手不吝赐教。
附程序段：
收不到时的发程序，子函数就省略了
int main(int argc)
{
int fd;
int nread;
char buff[8];
char *dev ="/dev/ttyS1";
fd = OpenDev(dev);
if (fd>;0)
set_speed(fd,19200);
else
{
printf("Can't Open Serial Port!\n";
exit(0);
}
if (set_Parity(fd,8,1,'N')== FALSE)
{
printf("Set Parity Error\n";
exit(1);
}
// while(1)
// {
if ((nread = read(fd,buff,7)>;0))
{
printf("\nLen %d\n",nread);
buff[nread]='\0';
printf("\n%s",buff);
}
else;
// }
close(fd);
exit(0);
}

能手到时的发程序：int main(int argc)
{
int fd;
int nread;
static char buff[5]={'a','b','c','d','e'};
char *dev ="/dev/ttyS0";
fd = OpenDev(dev);
if (fd>;0)
set_speed(fd,19200);
else
{
printf("Can't Open Serial Port!\n";
exit(0);
}
if (set_Parity(fd,8,1,'N')== FALSE)
{
printf("Set Parity Error\n";
exit(1);
}
// while(1)
// {
while((nread=write(fd,"abcf",)>;0)
{
printf("\nLen %d\n",nread);
// buff[nread]='\0';
printf("\n%s",buff);
}
// }
// close(fd);
// exit(0);
}
收程序都是一样的：
int main(int argc)
{
int fd;
int nread;
char buff[8];
char *dev ="/dev/ttyS1";
fd = OpenDev(dev);
if (fd>;0)
set_speed(fd,19200);
else
{
printf("Can't Open Serial Port!\n";
exit(0);
}
if (set_Parity(fd,8,1,'N')== FALSE)
{
printf("Set Parity Error\n";
exit(1);
}

while((nread=read(fd,buff,)>;0)
{
printf("\nLen %d\n",nread);
buff[nread]='\0';
printf("\n%s",buff);
}

// }
close(fd);
exit(0);
}