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MQTT与TCP的区别 - 创客硬件开发 - 清泛IT社区，为创新赋能！
...IoT概念也是在1999年，因此MQTT协议生逢其时。当时MIT Auto-ID Labs的Kevin Ashton为了把宝洁的供应链上的RFID标签和互联网连接起来，在1999年第一个提出了IoT这个概念。发明人TCP协议的发明人是Vinton Cerf（下图左，曾在IBM工作过两年）...
How do I properly clean up Excel interop objects?
I'm using the Excel interop in C# ( ApplicationClass ) and have placed the following code in my finally clause:
41 Answers
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How can I get the last 7 characters of a PHP string?
...characters are greater then 7 return last 7 characters else return the provided string.
or do this if you need to return message or error if length is less then 7
$newstring = (strlen($dynamicstring)>7)?substr($dynamicstring, -7):"message";
substr documentation
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Is a statically-typed full Lisp variant possible?
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Yes, it's very possible, although a standard HM-style type system is usually the wrong choice for most idiomatic Lisp/Scheme code. See Typed Racket for a recent language that is a "Full Lisp" (more like Scheme, actually) with static typing.
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Reduce, fold or scan (Left/Right)?
... operator's two arguments). This way we can cumulate a result.
reduceLeft and reduceRight cumulate a single result.
foldLeft and foldRight cumulate a single result using a start value.
scanLeft and scanRight cumulate a collection of intermediate cumulative results using a start value.
Accumulate...
Can you explain the HttpURLConnection connection process?
... a web service. I know how to use HTTPURLConnection but I want to understand how it works. Basically, I want to know the following:
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Why are C# 3.0 object initializer constructor parentheses optional?
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This question was the subject of my blog on September 20th 2010. Josh and Chad's answers ("they add no value so why require them?" and "to eliminate redundancy") are basically correct. To flesh that out a bit more:
The feature of allowing you to elide the argument list as part of the "larger f...
ab load testing
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The apache benchmark tool is very basic, and while it will give you a solid idea of some performance, it is a bad idea to only depend on it if you plan to have your site exposed to serious stress in production.
Having said that, here's the most common and simplest ...
How do I use vimdiff to resolve a git merge conflict?
I just merged a branch into my master in git and I got Automatic merge failed; fix conflicts and then commit the result. Now I ran git mergetool and vimdiff opened with the image below. I don't know how to use vimdiff. What does each panel here mean and how should I proceed to fix the merge conf...
Library? Static? Dynamic? Or Framework? Project inside another project
I have an existing iOS app and want to add a large chunk of code that I've been developing as another project just for ease of testing. The new chunk basically deals with saving an image to various sharing services, etc.. Because that sharing code needs a lot of testing and future updating, I was wo...