option | 易学教程

ubuntu16.04上安装配置DHCP服务的详细过程

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DHCP服务器是为客户端机器分配IP地址的，所有分配的IP地址都保存在DHCP服务器的数据库中。为了在子网中实现DHCP分配IP地址，需要在目标主机上安装配置DHCP服务。安装DHCP服务安装isc-dhcp-server： $ sudo apt install isc-dhcp-server 配置DHCP服务首先需要知道目标主机的网卡名称： $ ifconfig 得到以下信息： eno1 Link encap:Ethernet HWaddr e8:39:35:46:10:f5 UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:37752 errors:0 dropped:1 overruns:0 frame:0 TX packets:2202 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:2975927 (2.9 MB) TX bytes:226745 (226.7 KB) Interrupt:20 Memory:fe400000-fe420000 enx00e04c6802a0 Link encap:Ethernet HWaddr 00:e0:4c:68:02:a0 inet addr:10.11.12.13

How to disable multiple select options

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问题 How to disable multiple options in one select. For example i have 2 selects with 5 and 3 options. So if i select 3rd option in second select, i want to disable 3rd,4th and 5th option in first select: <select name="smjer"> <option value="1">1</option> <option value="2">2</option> <option value="3">3</option> <option value="4">4</option> <option value="5">5</option> </select> Second select: <select name="godina" > <option value="1" >1.</option> <option value="2" >2.</option> <option value="3">3

Bad cursor in select/option, IE

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问题 I have a problem with bad cursor in options when the text is under that. Normally, the option uses "default" cursor, but when eg. the paragraph is under option, in IE I see "text" cursor. Code: <form> <select> <option value=a selected="selected">First <option value=b>Second <option value=c>Third <option value=c>Fourth </select> <p>text</p> </form> It´s in IE11 and I think the older ones makes the same. I tried to set position: relative and z-index to select, option and paragraph, set cursor

Getopt optional arguments?

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问题 I have a program where you enter an option -d and then whether or not you supply a non-optional argument after the option, do something. Heres my code: #include <stdio.h> #include <getopt.h> #include <stdlib.h> #define OPT_LIST "d::" int main (int argc, char *argv[]) { int c; char string[] = "blah"; while ((c = getopt (argc, argv, OPT_LIST)) != -1) { switch (c) { case 'd': printf("%s\n", optarg); break; case '?': fprintf(stderr, "invalid option\n"); exit(EXIT_FAILURE); } } } So if you enter a

Option vs Exception in exception handling

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问题 After using F# option type for a while, I realize that it could be used for handling exceptional cases. I can use either option or Exception in the following examples: The find functions from List/Array/Seq modules raise KeyNotFoundException in uncommon cases, while corresponding tryFind counterparts return None in those situations. When I do backtracking (in solving N-queens, Sudoku, etc), whenever a branch has no solution, I can either raise an exception and catch it later or return None to

F# Option equivalent of C#'s ?? operator

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问题 I am looking for a way to get the value of an F# option or use a default value if it is None. This seems so common I can't believe something predefined doesn't exist. Here is how I do it right now: // val getOptionValue : Lazy<'a> -> Option<'a> -> 'a let getOptionValue (defaultValue : Lazy<_>) = function Some value -> value | None -> defaultValue.Force () I am (sort of) looking for the F# equivalent of the C# ?? operator: string test = GetString() ?? "This will be used if the result of

Is there a standard option workflow in F#?

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问题 Is there an option (maybe) wokflow (monad) in the standrd F# library? I've found a dozen of hand-made implementations (1, 2) of this workflow, but I don't really want to introduce non-standard and not very trusted code into my project. And all imaginable queries to google and msdn gave me no clue where to find it. 回答1: There's no Maybe monad in the standard F# library. You may want to look at FSharpx, a F# extension written by highly-qualified members of F# community, which has quite a number

Is there a standard option workflow in F#?

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Detect when a specific <option> is selected with jQuery

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问题 I'd like jQuery to detect when the option with the id trade_buy_max is selected. $(document).ready(function() { $("option#trade_buy_max").select(function () { //do something }); }); <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.1.0/jquery.min.js"></script> <select name='type' id='type'> <option id='trade_buy' value='1' selected='selected'>Buy</option> <option id='trade_buy_max' value='1'>Buy max</option> <option id='trade_sell' value='2'>Sell</option> <option id='trade_sell_max

Why is the use of Maybe/Option not so pervasive in Clojure?

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问题 Why does Clojure, despite such an emphasis on functional paradigm, not use the Maybe / Option monad to represent optional values? The use of Option is quite pervasive in Scala, a functional programming language I use regularly. 回答1: Clojure is not statically typed, so doesn't need the strict this/that/whatever type declarations that are necessary in haskell (and, I gather, Scala). If you want to return a string, you return a string; if you return nil instead, that's okay too. "Functional"