XML文件格式
<?xml version="1.0" encoding="utf-8"?>
<posts>
<row Id="4" PostTypeId="1" AcceptedAnswerId="7" CreationDate="2008-07-31T21:42:52.667" Score="735" ViewCount="59537" Body="<p>I want to use a <code>Track-Bar</code> to change a <code>Form</code>'s opacity.</p>
<p>This is my code:</p>
<pre class="lang-cs prettyprint-override"><code>decimal trans = trackBar1.Value / 5000;
this.Opacity = trans;
</code></pre>
<p>When I build the application, it gives the following error:</p>
<blockquote>
<pre class="lang-none prettyprint-override"><code>Cannot implicitly convert type decimal to double
</code></pre>
</blockquote>
<p>I have tried using <code>trans</code> and <code>double</code>, but then the <code>Control</code> doesn't work. This code worked fine in a past VB.NET project.</p>
" OwnerUserId="8" LastEditorUserId="3072350" LastEditorDisplayName="Rich B" LastEditDate="2021-02-26T03:31:15.027" LastActivityDate="2021-02-26T03:31:15.027" Title="How to convert a Decimal to a Double in C#?" Tags="<c#><floating-point><type-conversion><double><decimal>" AnswerCount="14" CommentCount="5" FavoriteCount="57" CommunityOwnedDate="2012-10-31T16:42:47.213" ContentLicense="CC BY-SA 4.0" />
<row Id="6" PostTypeId="1" AcceptedAnswerId="31" CreationDate="2008-07-31T22:08:08.620" Score="308" ViewCount="21813" Body="<p>I have an absolutely positioned <code>div</code> containing several children, one of which is a relatively positioned <code>div</code>. When I use a <code>percentage-based width</code> on the child <code>div</code>, it collapses to <code>0 width</code> on IE7, but not on Firefox or Safari.</p>
<p>If I use <code>pixel width</code>, it works. If the parent is relatively positioned, the percentage width on the child works.</p>
<ol>
<li>Is there something I'm missing here?</li>
<li>Is there an easy fix for this besides the <code>pixel-based width</code> on the child?</li>
<li>Is there an area of the CSS specification that covers this?</li>
</ol>
" OwnerUserId="9" LastEditorUserId="9134576" LastEditorDisplayName="user14723686" LastEditDate="2021-01-29T18:46:45.963" LastActivityDate="2021-01-29T18:46:45.963" Title="Why did the width collapse in the percentage width child element in an absolutely positioned parent on Internet Explorer 7?" Tags="<html><css><internet-explorer-7>" AnswerCount="7" CommentCount="1" FavoriteCount="12" ContentLicense="CC BY-SA 4.0" />
<row Id="7" PostTypeId="2" ParentId="4" CreationDate="2008-07-31T22:17:57.883" Score="488" Body="<p>An explicit cast to <code>double</code> like this isn't necessary:</p>

<pre><code>double trans = (double) trackBar1.Value / 5000.0;
</code></pre>

<p>Identifying the constant as <code>5000.0</code> (or as <code>5000d</code>) is sufficient:</p>

<pre><code>double trans = trackBar1.Value / 5000.0;
double trans = trackBar1.Value / 5000d;
</code></pre>
" OwnerUserId="9" LastEditorUserId="5496973" LastEditDate="2019-10-21T14:03:54.607" LastActivityDate="2019-10-21T14:03:54.607" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
<row Id="9" PostTypeId="1" AcceptedAnswerId="1404" CreationDate="2008-07-31T23:40:59.743" Score="2046" ViewCount="690121" Body="<p>Given a <code>DateTime</code> representing a person's birthday, how do I calculate their age in years?</p>
" OwnerUserId="1" LastEditorUserId="6537157" LastEditorDisplayName="Rich B" LastEditDate="2021-01-05T17:33:32.393" LastActivityDate="2021-08-14T13:35:38.050" Title="How do I calculate someone's age based on a DateTime type birthday?" Tags="<c#><.net><datetime>" AnswerCount="65" CommentCount="9" FavoriteCount="477" CommunityOwnedDate="2011-08-16T19:40:43.080" ContentLicense="CC BY-SA 4.0" />
<row Id="11" PostTypeId="1" AcceptedAnswerId="1248" CreationDate="2008-07-31T23:55:37.967" Score="1589" ViewCount="179860" Body="<p>Given a specific <code>DateTime</code> value, how do I display relative time, like:</p>

<ul>
<li>2 hours ago</li>
<li>3 days ago</li>
<li>a month ago</li>
</ul>
" OwnerUserId="1" LastEditorUserId="6479704" LastEditorDisplayName="user2370523" LastEditDate="2017-06-04T15:51:19.780" LastActivityDate="2021-09-01T21:49:09.617" Title="Calculate relative time in C#" Tags="<c#><datetime><time><datediff><relative-time-span>" AnswerCount="40" CommentCount="3" FavoriteCount="550" CommunityOwnedDate="2009-09-04T13:15:59.820" ContentLicense="CC BY-SA 3.0" />
<row Id="12" PostTypeId="2" ParentId="11" CreationDate="2008-07-31T23:56:41.303" Score="336" Body="<p>Here's how I do it</p>

<pre class="lang-csharp prettyprint-override"><code>var ts = new TimeSpan(DateTime.UtcNow.Ticks - dt.Ticks);
double delta = Math.Abs(ts.TotalSeconds);

if (delta &lt; 60)
{
 return ts.Seconds == 1 ? "one second ago" : ts.Seconds + " seconds ago";
}
if (delta &lt; 60 * 2)
{
 return "a minute ago";
}
if (delta &lt; 45 * 60)
{
 return ts.Minutes + " minutes ago";
}
if (delta &lt; 90 * 60)
{
 return "an hour ago";
}
if (delta &lt; 24 * 60 * 60)
{
 return ts.Hours + " hours ago";
}
if (delta &lt; 48 * 60 * 60)
{
 return "yesterday";
}
if (delta &lt; 30 * 24 * 60 * 60)
{
 return ts.Days + " days ago";
}
if (delta &lt; 12 * 30 * 24 * 60 * 60)
{
 int months = Convert.ToInt32(Math.Floor((double)ts.Days / 30));
 return months &lt;= 1 ? "one month ago" : months + " months ago";
}
int years = Convert.ToInt32(Math.Floor((double)ts.Days / 365));
return years &lt;= 1 ? "one year ago" : years + " years ago";
</code></pre>

<p>Suggestions? Comments? Ways to improve this algorithm?</p>
" OwnerUserId="1" LastEditorUserId="238419" LastEditorDisplayName="GateKiller" LastEditDate="2020-06-13T10:30:44.397" LastActivityDate="2020-06-13T10:30:44.397" CommentCount="10" CommunityOwnedDate="2009-09-04T13:15:59.820" ContentLicense="CC BY-SA 4.0" />
<row Id="13" PostTypeId="1" CreationDate="2008-08-01T00:42:38.903" Score="661" ViewCount="233241" Body="<p>Is there a standard way for a web server to be able to determine a user's timezone within a web page? </p>

<p>Perhaps from an HTTP header or part of the <code>user-agent</code> string?</p>
" OwnerUserId="9" LastEditorUserId="584192" LastEditorDisplayName="Rich B" LastEditDate="2020-12-03T03:37:56.313" LastActivityDate="2021-04-13T09:46:08.563" Title="Determine a user's timezone" Tags="<html><browser><timezone><user-agent><timezone-offset>" AnswerCount="26" CommentCount="9" FavoriteCount="157" ContentLicense="CC BY-SA 4.0" />
<row Id="14" PostTypeId="1" CreationDate="2008-08-01T00:59:11.177" Score="459" ViewCount="153984" Body="<p>What is the difference between <a href="<http://msdn.microsoft.com/en-us/library/9a6a2sxy.aspx">; rel="noreferrer"><code>Math.Floor()</code></a> and <a href="<http://msdn.microsoft.com/en-us/library/system.math.truncate.aspx">; rel="noreferrer"><code>Math.Truncate()</code></a> in .NET?</p>
" OwnerUserId="11" OwnerDisplayName="Anonymous User" LastEditorUserId="6495084" LastEditorDisplayName="Rich B" LastEditDate="2017-02-25T17:42:17.810" LastActivityDate="2021-04-22T05:49:24.453" Title="Difference between Math.Floor() and Math.Truncate()" Tags="<.net><math>" AnswerCount="13" CommentCount="1" FavoriteCount="64" ContentLicense="CC BY-SA 3.0" />
<row Id="16" PostTypeId="1" AcceptedAnswerId="12446" CreationDate="2008-08-01T04:59:33.643" Score="145" ViewCount="85904" Body="<p>How do you expose a LINQ query as an ASMX web service?
<br>
Usually, from the business tier, I can return a typed <code>DataSet</code> or a <code>DataTable</code> which can be serialized for transport over ASMX.</p>
<p>How can I do the same for a LINQ query? <br>
Is there a way to populate a typed <code>DataSet</code> or a <code>DataTable</code> via a LINQ query?</p>
<pre><code>public static MyDataTable CallMySproc()
{
 string conn = &quot;...&quot;;

 MyDatabaseDataContext db = new MyDatabaseDataContext(conn);
 MyDataTable dt = new MyDataTable();

 // execute a sproc via LINQ
 var query = from dr
 in db.MySproc().AsEnumerable
 select dr;

 // copy LINQ query resultset into a DataTable -this does not work ! 
 dt = query.CopyToDataTable();
 
 return dt;
}
</code></pre>
<p>How could I put the result set of a LINQ query into a <code>DataSet</code> or a <code>DataTable</code>?
<br>
Alternatively, can the LINQ query be serializable so that I can expose it as an ASMX web service?</p>
" OwnerUserId="2" LastEditorUserId="-1" LastEditorDisplayName="Chris Fournier" LastEditDate="2021-01-07T14:09:26.367" LastActivityDate="2021-01-07T14:09:26.367" Title="Filling a DataSet or a DataTable from a LINQ query result set" Tags="<c#><linq><web-services><.net-3.5>" AnswerCount="7" CommentCount="0" FavoriteCount="14" ContentLicense="CC BY-SA 4.0" />
<row Id="17" PostTypeId="1" AcceptedAnswerId="26" CreationDate="2008-08-01T05:09:55.993" Score="193" ViewCount="81531" Body="<p>How do I store binary data in <a href="<http://en.wikipedia.org/wiki/MySQL">; rel="noreferrer">MySQL</a>?</p>
" OwnerUserId="2" LastEditorUserId="584192" LastEditDate="2020-12-03T03:37:51.763" LastActivityDate="2020-12-03T03:37:51.763" Title="Binary Data in MySQL" Tags="<mysql><database><binary-data><data-storage>" AnswerCount="9" CommentCount="3" FavoriteCount="22" ClosedDate="2018-11-29T15:36:04.833" ContentLicense="CC BY-SA 3.0" />
<row Id="18" PostTypeId="2" ParentId="17" CreationDate="2008-08-01T05:12:44.193" Score="58" Body="<p>For a table like this:</p>

<pre><code>CREATE TABLE binary_data (
 id INT(4) NOT NULL AUTO_INCREMENT PRIMARY KEY,
 description CHAR(50),
 bin_data LONGBLOB,
 filename CHAR(50),
 filesize CHAR(50),
 filetype CHAR(50)
);
</code></pre>

<p>Here is a PHP example:</p>

<pre><code>&lt;?php
 // store.php3 - by Florian Dittmer &lt;[email protected]&gt;
 // Example php script to demonstrate the storing of binary files into
 // an sql database. More information can be found at <http://www.phpbuilder.com/
?&gt;

&lt;html&gt;
>; &lt;head&gt;&lt;title&gt;Store binary data into SQL Database&lt;/title&gt;&lt;/head&gt;

 &lt;body&gt;
 &lt;?php
 // Code that will be executed if the form has been submitted:

 if ($submit) {
 // Connect to the database (you may have to adjust
 // the hostname, username or password).

 mysql_connect("localhost", "root", "password");
 mysql_select_db("binary_data");

 $data = mysql_real_escape_string(fread(fopen($form_data, "r"), filesize($form_data)));

 $result = mysql_query("INSERT INTO binary_data (description, bin_data, filename, filesize, filetype) ".
 "VALUES ('$form_description', '$data', '$form_data_name', '$form_data_size', '$form_data_type')");

 $id= mysql_insert_id();
 print "&lt;p&gt;This file has the following Database ID: &lt;b&gt;$id&lt;/b&gt;";

 mysql_close();
 } else {

 // else show the form to submit new data:
 ?&gt;
 &lt;form method="post" action="&lt;?php echo $PHP_SELF; ?&gt;" enctype="multipart/form-data"&gt;
 File Description:&lt;br&gt;
 &lt;input type="text" name="form_description" size="40"&gt;
 &lt;input type="hidden" name="MAX_FILE_SIZE" value="1000000"&gt;
 &lt;br&gt;File to upload/store in database:&lt;br&gt;
 &lt;input type="file" name="form_data" size="40"&gt;
 &lt;p&gt;&lt;input type="submit" name="submit" value="submit"&gt;
 &lt;/form&gt;

 &lt;?php
 }
 ?&gt;
 &lt;/body&gt;
&lt;/html&gt;
</code></pre>
" OwnerDisplayName="phpguy" LastEditorUserId="126039" LastEditorDisplayName="Jeff Atwood" LastEditDate="2016-06-02T05:56:26.060" LastActivityDate="2016-06-02T05:56:26.060" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
<row Id="19" PostTypeId="1" AcceptedAnswerId="531" CreationDate="2008-08-01T05:21:22.257" Score="334" ViewCount="60265" Body="<p>I'm looking for the fastest way to obtain the value of π, as a personal challenge. More specifically, I'm using ways that don't involve using <code>#define</code> constants like <code>M_PI</code>, or hard-coding the number in.</p>

<p>The program below tests the various ways I know of. The inline assembly version is, in theory, the fastest option, though clearly not portable. I've included it as a baseline to compare against the other versions. In my tests, with built-ins, the <code>4 * atan(1)</code> version is fastest on GCC 4.2, because it auto-folds the <code>atan(1)</code> into a constant. With <code>-fno-builtin</code> specified, the <code>atan2(0, -1)</code> version is fastest.</p>

<p>Here's the main testing program (<code>pitimes.c</code>):</p>

<pre class="lang-c prettyprint-override"><code>#include &lt;math.h&gt;
#include &lt;stdio.h&gt;
#include &lt;time.h&gt;

#define ITERS 10000000
#define TESTWITH(x) { \\
 diff = 0.0; \\
 time1 = clock(); \\
 for (i = 0; i &lt; ITERS; ++i) \\
 diff += (x) - M_PI; \\
 time2 = clock(); \\
 printf("%s\\t=&gt; %e, time =&gt; %f\\n", #x, diff, diffclock(time2, time1)); \\
}

static inline double
diffclock(clock_t time1, clock_t time0)
{
 return (double) (time1 - time0) / CLOCKS_PER_SEC;
}

int
main()
{
 int i;
 clock_t time1, time2;
 double diff;

 /* Warmup. The atan2 case catches GCC's atan folding (which would
 * optimise the ``4 * atan(1) - M_PI'' to a no-op), if -fno-builtin
 * is not used. */
 TESTWITH(4 * atan(1))
 TESTWITH(4 * atan2(1, 1))

#if defined(__GNUC__) &amp;&amp; (defined(__i386__) || defined(__amd64__))
 extern double fldpi();
 TESTWITH(fldpi())
#endif

 /* Actual tests start here. */
 TESTWITH(atan2(0, -1))
 TESTWITH(acos(-1))
 TESTWITH(2 * asin(1))
 TESTWITH(4 * atan2(1, 1))
 TESTWITH(4 * atan(1))

 return 0;
}
</code></pre>

<p>And the inline assembly stuff (<code>fldpi.c</code>) that will only work for x86 and x64 systems:</p>

<pre class="lang-c prettyprint-override"><code>double
fldpi()
{
 double pi;
 asm("fldpi" : "=t" (pi));
 return pi;
}
</code></pre>

<p>And a build script that builds all the configurations I'm testing (<code>build.sh</code>):</p>

<pre><code>#!/bin/sh
gcc -O3 -Wall -c -m32 -o fldpi-32.o fldpi.c
gcc -O3 -Wall -c -m64 -o fldpi-64.o fldpi.c

gcc -O3 -Wall -ffast-math -m32 -o pitimes1-32 pitimes.c fldpi-32.o
gcc -O3 -Wall -m32 -o pitimes2-32 pitimes.c fldpi-32.o -lm
gcc -O3 -Wall -fno-builtin -m32 -o pitimes3-32 pitimes.c fldpi-32.o -lm
gcc -O3 -Wall -ffast-math -m64 -o pitimes1-64 pitimes.c fldpi-64.o -lm
gcc -O3 -Wall -m64 -o pitimes2-64 pitimes.c fldpi-64.o -lm
gcc -O3 -Wall -fno-builtin -m64 -o pitimes3-64 pitimes.c fldpi-64.o -lm
</code></pre>

<p>Apart from testing between various compiler flags (I've compared 32-bit against 64-bit too because the optimizations are different), I've also tried switching the order of the tests around. But still, the <code>atan2(0, -1)</code> version still comes out on top every time.</p>
" OwnerUserId="13" LastEditorUserId="3768871" LastEditorDisplayName="Chris Jester-Young" LastEditDate="2019-05-15T01:33:48.730" LastActivityDate="2021-01-30T09:12:42.477" Title="What is the fastest way to get the value of π?" Tags="<performance><algorithm><language-agnostic><unix><pi>" AnswerCount="22" CommentCount="17" FavoriteCount="83" ContentLicense="CC BY-SA 4.0" />
<row Id="22" PostTypeId="2" ParentId="9" CreationDate="2008-08-01T12:07:19.500" Score="51" Body="<p>The best way that I know of because of leap years and everything is:</p>

<pre class="lang-cs prettyprint-override"><code>DateTime birthDate = new DateTime(2000,3,1);
int age = (int)Math.Floor((DateTime.Now - birthDate).TotalDays / 365.25D);
</code></pre>
" OwnerUserId="17" LastEditorUserId="63550" LastEditorDisplayName="Nick" LastEditDate="2020-02-29T01:31:43.697" LastActivityDate="2020-02-29T01:31:43.697" CommentCount="0" CommunityOwnedDate="2011-08-16T19:40:43.080" ContentLicense="CC BY-SA 4.0" />
<row Id="24" PostTypeId="1" AcceptedAnswerId="49" CreationDate="2008-08-01T12:12:19.350" Score="186" ViewCount="91128" Body="<p>If I have a trigger before the update on a table, how can I throw an error that prevents the update on that table?</p>
" OwnerUserId="22" LastEditorUserId="14152908" LastEditorDisplayName="Jim Anderson" LastEditDate="2021-01-29T12:57:17.153" LastActivityDate="2021-01-29T12:57:17.153" Title="Throw an error preventing a table update in a MySQL trigger" Tags="<mysql><database><triggers>" AnswerCount="7" CommentCount="0" FavoriteCount="27" ContentLicense="CC BY-SA 4.0" />
<row Id="25" PostTypeId="1" AcceptedAnswerId="1443907" CreationDate="2008-08-01T12:13:50.207" Score="173" ViewCount="14731" Body="<p>I'm having issues getting the C sockets API to work properly in C++ on z/OS.</p>
<p>Although I am including <code>sys/socket.h</code>, I still get compile time errors telling me that <code>AF_INET</code> is not defined.</p>
<p>Am I missing something obvious, or is this related to the fact that being on z/OS makes my problems much more complicated?</p>
<p>I discovered that there is an <code>#ifdef</code> that I'm hitting. Apparently z/OS isn't happy unless I define which &quot;type&quot; of sockets I'm using with:</p>
<pre><code>#define _OE_SOCKETS
</code></pre>
<p>Now, I personally have no idea what this <code>_OE_SOCKETS</code> is actually for, so if any z/OS sockets programmers are out there (all 3 of you), perhaps you could give me a rundown of how this all works?</p>
<p>Test App</p>
<pre><code>#include &lt;sys/socket.h&gt;

int main()
{
 return AF_INET;
}
</code></pre>
<p>Compile/Link Output:</p>
<pre><code>cxx -Wc,xplink -Wl,xplink -o inet_test inet.C

&quot;./inet.C&quot;, line 5.16: CCN5274 (S) The name lookup for &quot;AF_INET&quot; did not find a declaration.
CCN0797(I) Compilation failed for file ./inet.C. Object file not created.
</code></pre>
<p>A check of sys/sockets.h does include the definition I need, and as far as I can tell, it is not being blocked by any <code>#ifdef</code> statements.</p>
<p>I have however noticed it contains the following:</p>
<pre><code>#ifdef __cplusplus
 extern &quot;C&quot; {
#endif
</code></pre>
<p>which encapsulates basically the whole file? Not sure if it matters.</p>
" OwnerUserId="23" LastEditorUserId="792066" LastEditorDisplayName="user5857081" LastEditDate="2020-12-02T17:23:58.717" LastActivityDate="2020-12-02T17:23:58.717" Title="How to use the C socket API in C++ on z/OS" Tags="<c++><c><sockets><mainframe><zos>" AnswerCount="9" CommentCount="1" FavoriteCount="9" ContentLicense="CC BY-SA 4.0" />
<row Id="26" PostTypeId="2" ParentId="17" CreationDate="2008-08-01T12:16:22.167" Score="140" Body="<p>The answer by phpguy is correct but I think there is a lot of confusion in the additional details there.</p>

<p>The basic answer is in a <code>BLOB</code> data type / attribute domain. <strong>BLOB</strong> is short for Binary Large Object and that column data type is specific for handling binary data.</p>

<p>See <a href="<http://dev.mysql.com/doc/refman/5.7/en/blob.html">; rel="noreferrer">the relevant manual page for MySQL</a>.</p>
" OwnerUserId="48" OwnerDisplayName="Mat Scales" LastEditorUserId="126039" LastEditorDisplayName="Geoff Dalgas" LastEditDate="2016-06-02T05:55:17.060" LastActivityDate="2016-06-02T05:55:17.060" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
</posts>
读取大型XML文件并写入大型csv文件
import xml.etree.ElementTree as et
import csv
# 创建（如果文件存在会删除重新创建）csv文件并写入header
with open(output_file, "w") as f:
writer = csv.writer(f)
writer.writerow(["Id", "CreationDate", ...])
# 创建input_file（XML）的迭代器，每读到一个开始标签和结束标签都会触发对应的事件
context = et.iterparse(input_file, events=("start", "end"))
context = iter(context)
# 获取第一个节点，也就是根节点<posts>
ev, root = next(context)
# 创建缓冲区，用来写入csv文件
buffer = []
# 迭代XML文件
for ev, el in context:
if ev == "start" and el.tag == "row":
row = [el.attrib["Id"], el.attrib["CreationDate"], ...] # 得到row数据
buffer.append(row) # 添加到缓冲区
if len(buffer) == 1000:
# 缓冲区有了1000条数据，写入（追加）到csv文件里
with open(output_file, 'a') as f:
writer = csv.writer(f)
writer.writerows(buffer)
buffer.clear() # 清空缓冲区
# 清除<posts>节点里添加的row子节点，可以避免占用内存，这样当读完xml文件，<posts>节点里也不会记录任何row子节点
root.clear()
# 将缓冲区剩余的row存入csv文件里
if len(buffer) != 0:
with open(output_file, 'a') as f:
writer = csv.writer(f)
writer.writerows(buffer)
buffer.clear() # 清空缓冲区
写入成功后的csv文件
