Lowyat.NET: Latest topics by WongGei

Newbie, junior, senior programmer

WongGei — Mon, 20 Feb 2023 12:29:39 +0800

Requirement,

Create a simple POS system that take in customer order and calculates the total amount of the order.

This seems like a simple question that suits 1st assignment of the programming language class.

Let see how the Newbie, Junior Programmer, Senior Programmers' work.

And discuss why the program classified as such (N,J,S)

Wireguard

WongGei — Thu, 19 May 2022 18:43:37 +0800

Anyone familiar with VPN using Wiregaurd?

I'm trying out this opensource VPN to build a virtual private network of my own.

Manage to let pc102 (192.168.226.102) and pc158 (192.168.227.158) talk to each other via ping.

The problem annoying me is that pc102 is unable to ping the external address of gw226 (10.10.0.2) , but able to ping gw227 (10.10.0.3).
Same apply to pc158, unable to ping gw227 (10.10.0.3) but can ping gw226 (10.10.0.2).

Any comment?

10.235.17.206%200

WongGei — Sat, 30 May 2020 15:49:22 +0800

Hi all.

As refer to the title, I received a list of IPv4 addresses and there are some extra things (%200) at the back.
Try to google it but no luck.
May I know what is the %200 after the IP?

192.168.1.101%enp0s3:68

I know
192.168.1.101 is the IPv4 address.
:68 is the port
But what is %enp0s3 (<-after percentage, the enp0s3 is the network device)

Linux traffic control

WongGei — Wed, 30 Nov 2016 17:06:03 +0800

Hi, I am trying to emulate a network traffic environment using linux tc command.

Testing scenario:

3 network with different bandwidth and latency between them.

A 192.168.100.xxx
B 192.168.101.xxx
C 192.168.102.xxx

A - B, max bandwidth = 100M, latency 10ms
A - C, max bandwidth = 1M, latency 300ms
B - C, max bandwidth = 10M, latency 100ms

I use tc-htb to do traffic control

tc qdisc del root dev eth1

tc qdisc add dev eth1 root handle 1: htb default 1

tc class add dev eth1 parent 1: classid 1:1 htb rate 1000mbps burst 15k
tc class add dev eth1 parent 1:1 classid 1:10 htb rate 100mbit ceil 100mbit burst 15k
tc class add dev eth1 parent 1:1 classid 1:20 htb rate 10mbit ceil 10mbit burst 15k
tc class add dev eth1 parent 1:1 classid 1:30 htb rate 1mbit ceil 1mbit burst 15k

tc qdisc add dev eth1 parent 1:10 handle 10: sfq perturb 10
tc qdisc add dev eth1 parent 1:20 handle 20: sfq perturb 10
tc qdisc add dev eth1 parent 1:30 handle 30: sfq perturb 10

tc filter add dev eth1 parent 1: protocol ip prio 2 u32 match ip src 192.168.100.0/24 flowid 1:10
tc filter add dev eth1 parent 1: protocol ip prio 2 u32 match ip src 192.168.101.0/24 flowid 1:20
tc filter add dev eth1 parent 1: protocol ip prio 2 u32 match ip src 192.168.102.0/24 flowid 1:30

I manage to control the bandwidth.
May I know how to add in the control of latency?

C++11 default parameter

WongGei — Wed, 04 Sep 2013 13:56:41 +0800

Hi All

Playing with the new C++11 Lambda function.

Would like to create a Container class that will arrange() itself.

CODE

class Cont c;

c.arrange(); //sort ascending, default action

c.arrange([](int l,int r){return l > r;}); //sort descending, using Lambda function

c.arrange(greater<int>()); //sort descending using std::binary_functions

Anyone know how to declare the Cont class for arrange()?

C++ and STL

WongGei — Tue, 25 Oct 2011 22:28:12 +0800

Just wonder which one is more familiar to you.

C/C++ private lesson

WongGei — Tue, 04 Oct 2011 21:49:28 +0800

Private lesson offer to those who are at Klang Valley.

PM me or mail to wonggei@gmail.com

Interesting C code

WongGei — Fri, 07 Dec 2007 16:20:26 +0800

Try this simple code and see the result.

Why?

#include <stdio.h>

int main ( int argc , char *argv[] )
{
int i = 0;

printf ( "%d" , i++ );
printf ( "%d" , i++ );

i=0;

printf ( "%d" , ++i );
printf ( "%d" , ++i );

i=0;

printf ("%d%d", i++ , i++ );

i=0;

printf ("%d%d", ++i , ++i );

return 0;
}

Hard to explain even for U professor.