fopen, access and stat 執行效能的比較

fopen, access, and stat是常用來檢查檔案是否存在的c library

本篇文章就執行效能來做一個比較

檔案存在

	fopen	access	stat
time	Tue Nov 24 13:36:27 2015 Tue Nov 24 13:36:45 2015 Total time: 18s	Tue Nov 24 13:36:45 2015 Tue Nov 24 13:36:52 2015 Total time: 7s	Tue Nov 24 13:36:52 2015 Tue Nov 24 13:36:59 2015 Total time: 7s

檔案不存在

	fopen	access	stat
time	Tue Nov 24 13:38:21 2015 Tue Nov 24 13:38:34 2015 Total time: 13s	Tue Nov 24 13:38:34 2015 Tue Nov 24 13:38:41 2015 Total time: 7s	Tue Nov 24 13:38:41 2015 Tue Nov 24 13:38:48 2015 Total time: 7s

結果:

stat跟access不相上下

stat, access都比fopen快

source code download:
https://github.com/nelsonchung/nelson_sample_code_for_c/blob/master/diff_fopen_access_stat.c

Sample code of dhcp client to send dhcp discover, request and inform

參考 Implement DHCP client

增加dhcp request and inform packet的發送功能

dhcp.c

http://pastie.org/pastes/8294244/text

build on Ubuntu 12.04.1 with gcc 4.6.3
gcc dhcp.c
./a.out
輸入1發送dhcp discover
輸入3發送dhcp request
輸入8發送dhcp inform

How to interpret complex C/C++ declarations

Ref:
http://www.codeproject.com/Articles/7042/How-to-interpret-complex-C-C-declarations#right_left_rule

又更懂c語言的pointer and reference觀念後, 又覺得自己不會c語言

C/C++之指標 (pointer)，參考 (reference) 觀念整理與常見問題

對於c語言

call by value,

call by pointer/address講解的非常清楚 

你還可以了解到pointer to pointer, reference to pointer

以下是我實踐的代碼

供自己日後閱讀

 心得就撰寫在代碼裡

 

閱讀複雜pointer代碼的操作心法

The right-left rule