这里打算记录一些平时遇到的，大家可能不会太留意，但有趣的小知识。
1：CRLF
CRLF的含义是“carriage return/line feed”，意思就是回车。这是两个ASCII字符，分别排在第十三和第十位。
CR和LF是在计算机终端还是电传打印机的时候遗留下来的东西。电传打字机就像普通打字机一样工作。在每一行的末端，CR命令让打印头回到左边。LF命令让纸前进一行。
虽然使用卷纸的终端时代已经过去了，但是，CR和LF命令依然存在，许多应用程序和网络协议仍使用这些命令作为分隔符。
2: ICMP 和 windows
刚才碰到一个问题: ping同一个网段的一个主机,竟然返回destinationunreachable.害我以为是本机的路由表出了问题排查了很久,后来在这里发现是WIN7的ICMP实现没有遵循RFC标准. 实际的情况是子网内做了MAC白名单或者MAC绑定,让我的机子不在列表内. 对于这种情况,标准的ICMP应该返回time
out而不是微软的destinationunreachable.
3: CMCC自动转跳登录页面
刚才一个同事连接CMCC后, 打开网页不能自动转跳到CMCC的登录页面. 在网上搜到说可能是手动设置了DNS服务器, 需要改成自动获取. 略一思忖, 哈哈, 原来它们是用DNS劫持去实现这个自动转跳的. 至于验证, 用wireshark抓包就可以了.
4: C语言中的#pragma
来自:http://stackoverflow.com/questions/3791259/where-does-the-word-pragma-come-from
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According to a US Government-owned(!) document describing the design of Ada: Rationale
for the Design of the Ada® Programming Language :
A pragma (from the Greek word meaning action) is used to direct the actions of the compiler in particular ways, but has no effect on the semantics of a program (in general).
I like the (last caveat) there...
This cross references well with on-line greek dictionaries (e.g. as quoted by Martin
York) that say pragma (πραγμα, as commented on the original question by asveikau) means:
a. that which has been done, a deed, an accomplished fact
b. what is done or being accomplished
.spec. business, a commercial transaction
c. a matter, question, affair
.spec. in a forensic sense, a matter at law, case, suit
d. that which is or exists, a thing
Seems the key to understanding is the word action rather than information.
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