#ifndef EXAMPLES_WATCHED_H
#define EXAMPLES_WATCHED_H
#ifdef __cplusplus
extern "C" {
#endif
void init_watched(void);
#ifdef __cplusplus
}
#endif
#endif /* EXAMPLES_WATCHED_H */
watched.c文件：
/*
* start by including the appropriate header files
*/
#include <net-snmp/net-snmp-config.h>
#include <net-snmp/net-snmp-includes.h>
#include <net-snmp/agent/net-snmp-agent-includes.h>
void init_watched_string(void);
void init_watched(void)
{
init_watched_string();
}
void init_watched_string(void)
{
/*
* the storage for our string. It must be static or allocated.
* we use static here for simplicity.
*/
static char my_string[256] = "welcome to vcsky.net!";
/*
* the OID we want to register our string at. This should be a
* fully qualified instance. In our case, it's a scalar at:
* NET-SNMP-EXAMPLES-MIB::netSnmpExampleString.0 (note the trailing
* 0 which is required for any instantiation of any scalar object)
*/
oid my_registration_oid[] =
{ 1, 3, 6, 1, 4, 1, 8072, 2, 1, 3, 0 };
/*
* variables needed for registration
*/
netsnmp_handler_registration *reginfo;
static netsnmp_watcher_info watcher_info;
int watcher_flags;
/*
* a debugging statement. Run the agent with -Dexample_string_instance
* to see the output of this debugging statement.
*/
DEBUGMSGTL(("example_string_instance",
"Initalizing example string instance. Default value = %s\n",
my_string));
/*
* If we wanted a callback when the value was retrieved or set
* (even though the details of doing this are handled for you),
* you could change the NULL pointer below to a valid handler
* function.
*
* Change RWRITE to RONLY for a read-only string.
*/
reginfo = netsnmp_create_handler_registration("my example string", NULL,
my_registration_oid,
OID_LENGTH(my_registration_oid),
HANDLER_CAN_RWRITE);
/*
* the three options for a string watcher are:
* fixed size string (length never changes)
* variable size (length can be 0 - MAX, for some MAX)
* c string (length can be 0 - MAX-1 for some max, \0 is not a valid
* character in the string, the length is provided by strlen)
*
* we'll use a variable length string.
*/
watcher_flags =WATCHER_MAX_SIZE;
/*
* create the watcher info for our string.
*/
netsnmp_init_watcher_info6(&watcher_info, my_string, strlen(my_string),
ASN_OCTET_STR, watcher_flags,
sizeof(my_string), NULL);
/*
* the line below registers our "my_string" variable above as
* accessible and makes it writable.
*/
netsnmp_register_watched_instance(reginfo, &watcher_info);
DEBUGMSGTL(("example_string_instance",
"Done initalizing example string instance\n"));
}
编译运行（注意在入口函数中将init_nstAgentSubagentObject替换为init_watched）。
打开cmd，测试一下：snmpget -v1 -c public localhost 1.3.6.1.4.1.8072.2.1.3.0
返回结果：NET-SNMP-MIB::netSnmp.2.1.3.0 = STRING: "welcome to vcsky.net!" snmpset -v1 -c public localhost 1.3.6.1.4.1.8072.2.1.3.0 s "havenzhao”
返回结果：NET-SNMP-MIB::netSnmp.2.1.3.0 = STRING: "havenzhao" OK，没问题！ 接下来，我们想改变my_string这个变量的值，这个值需要从程序的其它地方获得，这样才能起到监测的作用。先简单改变一下试试看，能否正确运行： 修改下watched.c文件，添加一行为my_string改变值的语句，标红的代码即是。
#include <net-snmp/net-snmp-config.h> #include <net-snmp/net-snmp-includes.h> #include <net-snmp/agent/net-snmp-agent-includes.h>
static char
my_string[256] = "welcome to vcsky.net!"; //作为全局变量
void change_string_value()
{
strcpy(my_string, "haven zhao");
}
void init_watched_string(void);
void init_watched(void)
{
init_watched_string();
}
void init_watched_string(void)
{
oid my_registration_oid[] =
{ 1, 3, 6, 1, 4, 1, 8072, 2, 1, 3, 0 };
netsnmp_handler_registration *reginfo;
static netsnmp_watcher_info watcher_info;
int watcher_flags;
DEBUGMSGTL(("example_string_instance",
"Initalizing example string instance. Default value = %s\n",
my_string));
reginfo = netsnmp_create_handler_registration("my example string", NULL,
my_registration_oid,
OID_LENGTH(my_registration_oid),
HANDLER_CAN_RWRITE);
watcher_flags = WATCHER_MAX_SIZE;
netsnmp_init_watcher_info6(&watcher_info, my_string, strlen(my_string),
ASN_OCTET_STR, watcher_flags,
sizeof(my_string), NULL);
netsnmp_register_watched_instance(reginfo, &watcher_info);
DEBUGMSGTL((“example_string_instance”,
“Done initalizing example string instance\n”));
}
/* if you use select(), see snmp_select_info() in snmp_api(3) */
/* --- OR --- */
change_string_value(); //放在这里了
agent_check_and_process(1); /* 0 == don't block */
}