C++ string

若要在string 後面在連接其他字串的方法有三種, 可是效率卻不同，假設要在字串str 後面加其他字串word

#include
string str, word;

方法1：
str += word;

方法2：
str = str.append(word);

方法3：
str = str + word;



效率比較
方法1 = 方法2 > 方法3

方法3會將字串str + word複製到一個記憶體空間，再將記憶體空間內的值指派到str 內, 所以多花了一倍時間

InfiniBand on Redhat/Centos Linux.

## install necessary packages
yum install ibutils.x86_64 openib.noarch opensm.x86_64 infiniband-diags.x86_64

## client
yum install ibutils.x86_64 openib.noarch infiniband-diags.x86_64

## start services
service openibd start
service opensmd start

## configure interface


DEVICE=ib0     
TYPE=Infiniband     
BOOTPROTO=static     
BROADCAST=192.168.0.255     
IPADDR=192.168.0.1     
NETMASK=255.255.255.0 
NETWORK=192.168.0.0     
ONBOOT=yes



net.ipv4.conf.all.arp_ignore=1
net.ipv4.conf.ib0.arp_ignore=1
net.ipv4.conf.ib1.arp_ignore=1

references:
HOWTO: Getting Started with InfiniBand on Redhat/Centos Linux.

How to suspend process

今天有人問我在Linux 下要如何將行程暫停, 這個問題我從來沒想過. 用Google 查了一下發現用kill 就行了.

kill -stop PID  #suspend process

kill -cont PID  #restart process

How to query dependencies from RPM file or packages

rpm -qpR {.rpm-file}

rpm -qR {package-name}

How to list packages in Ubuntu

dpkg --get-selections > packages

References:

http://www.cyberciti.biz/faq/how-do-i-find-what-dependencies-a-rpm-file-has/
http://askubuntu.com/questions/17823/how-to-list-all-installed-packages

swap two variable

For Interger
x ^= y;
y ^= x;
x ^= y;

For Float numberx=x+y;
y=x-y;
x=x-y;