Nagios error for monitoring routers

I have installed nagios 3.5 X64 on centos 6.4 to monitor routers and switches.

when I try to define hosts in config file like the tutorials in nagios.conf I recive error.
[[email protected] ~]# whereis nagios
nagios: /usr/sbin/nagios /etc/nagios /usr/lib64/nagios /usr/include/nagios /usr/share/nagios
i added /usr/sbin/nagios to the path and then I did /usr/sbin/nagios -v /etc/nagios/nagios.cfg

the result is:
Error in configuration file ‘/etc/nagios/nagios.cfg’ - Line 47 (NULL value)
Error processing main config file!
this is the line 47 :
vi +47 /etc/nagios/nagios.cfg
**define **host {
name linuxsrv-server ; The name of this host template
use generic-host ; Inherit default values from the generic-host template
check_period 24x7 ; By default, Windows servers are monitored round the clock
check_interval 1 ; Actively check the server every 5 minutes
retry_interval 1 ; Schedule host check retries at 1 minute intervals
max_check_attempts 10 ; Check each server 10 times (max)
"/etc/nagios/nagios.cfg" 1393L, 46319C
i used this configuration according to the official nagios documents
is there any idea what the problem may be?