• 题目大概是问什么时候用 offer() 什么时候用 put()， 因为他们的implemention其实不一样，offer 是用 balking，就是如果出错就忽视, 或者throw exception。 put 就是如果满了就call wait()。 所以我的问题是什么时候...
• is the difference between cout, cerr, clog of iostream header in c++? When to use which one? stdout and stderr are different streams, even though they both refer to console output by defau


What
is the difference between cout, cerr, clog of iostream header in c++? When to use which one?

stdout and stderr are different streams, even though they both refer to console output by default. Redirecting (piping) one of them (e.g. program.exe
>out.txt) would not affect the other.

Generally, stdout should be used for actual program output, while all information and error messages should be printed to stderr, so that if the user redirects output to a file, information messages are still printed on the screen and not to the output file.
以前关于什么时候用cout, 什么时候用cerr有比较大的随意性质，总结一下：显式print 一定要用std::cout, 其余情况，用情况主要用std::cerr
class ClassA
{
void print()
{
std::cout<<....
}
};


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• 这个问题真蛋疼，真的，因为你不知道它什么时候就跑出来了，而且一旦出这个问题，运气好的可以通过所谓的度娘找到替换一个名为tcnative-1.dll文件解决掉这个问题，运气不好的，呵呵。。。。我一共遇到两次，第一次的...
这个问题真蛋疼，真的，因为你不知道它什么时候就跑出来了，而且一旦出这个问题，运气好的可以通过所谓的度娘找到替换一个名为tcnative-1.dll文件解决掉这个问题，运气不好的，呵呵。。。。我一共遇到两次，第一次的时候折腾够呛，但是最后也算是通过替换那个文件解决了问题，可是好景不长，用了没几天，突然就又出现这个错误了，对于网上千篇一律的替换文件的方法我已不愿再去尝试了，因为我几乎试尽了那些方法，不奏效目前我也没有找到解决这个问题的办法，但是如果你着急调试程序，而tomcat却起不来，可以试试我这招，可以让你暂时避开这个问题继续调试程序，等闲暇的时候再回来解决这个问题！！！ 方法很简单：打开conf/server.xml这个配置文件找到下面这行：1234567891011<Server port="8005" shutdown="SHUTDOWN">   <!--APR library loader. Documentation at /docs/apr.html --><br><!-- 下面这行本来是没有注释的，现在将这一行注释了，你的问题就暂时不会出现了 -->  <!--<Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" />-->  <!--Initialize Jasper prior to webapps are loaded. Documentation at /docs/jasper-howto.html -->  <Listener className="org.apache.catalina.core.JasperListener" />  <!-- Prevent memory leaks due to use of particular java/javax APIs-->  <Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener" />  <!-- JMX Support for the Tomcat server. Documentation at /docs/non-existent.html -->  <Listener className="org.apache.catalina.mbeans.ServerLifecycleListener" />  <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" />　　看到了吧，将 <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" /> 这行配置注释了即可关闭APR
至于问题最完美的解决方案，我这里还没有，只能解一时之需，不影响工作进度。
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• ... <pre><code><?...header("Content-type: text/css; charset=utf-8");...<p>It works fine on my side in all browsers, but I have read some people are ... Under which situation this problem shows up? </div>
• hibernate属性文件配置C3P0连接池的时候，hibernate.c3p0.timeout与hibernate.c3p0.idle_test_period这两个属性各是什么意思，有何区别？ Hiberante实战 这本书里是这样写的： hibernate.c3p0.timeout：You ...
• 各位好，我在libcurl的接口往localhost服务器上传文件里上传文件的时候出现了下面的错误（的机器系统是linuxmint17，搭建的服务器Apache + PHP5 + MySQL） *** We read 4257 bytes from file <!DOCTYPE ...
• We live in a world in which education and knowledge is literally at our fingertips, and it’s never been easier to pick up a new skill or hobby. Make it a habit to learn something new every day, and ...
• The App_Code folder can contain subdirectories of files, which can include class files that in different programming languages. For more information, see Shared Code Folders in ASP.NET Web Site ...
• 3：还有一个信息不知道有没有：奇怪的是，我把代码"E:\\vc\\column.txt")中的column改成text,却成功通过编译 运行结果也正常（之前学习输入输出流这一章节的时候，做过一个例题，是以text.txt命名的） 4：求助。...
• 不知道什么时候用Subquery 先上题： For each instrument, show its type, maker, the owner’s name, the corresponding orchestra name, and the number of concerts (name this column as concert_number) in ...
不知道什么时候用Subquery
先上题：
For each instrument, show its type, maker, the owner’s name, the corresponding orchestra name, and the number of concerts (name this column as concert_number) in which the owner played from 2013 to 2016. Take into consideration only instruments produced in 2013 or earlier.
SELECT
instruments.type,
instruments.maker,
members.name,
orchestras.name,
(SELECT COUNT (concerts.orchestra_id)
FROM concerts
WHERE concerts.year BETWEEN 2013 AND 2016 AND concerts.orchestra_id=orchestras.id) AS concert_number
FROM instruments
JOIN members
ON members.id = owner_id
JOIN orchestras
ON orchestras.id = members.orchestra_id
WHERE instruments.production_year<=2013;
为什么不用group by 来计算 number of concerts ？
we have a subquery in the SELECT clause, and we are counting number of concerts in the subquery itself. The way this subquery is running is, it is adding one value for each row(returned by the main query) and that value is same as the count of concerts performed between year 2013 and 2016 by that respective orchestra, that’s why you have c.orchestra_id=o.id.
例题：
For each orchestra, show a report consisting of:
Name of the orchestra as the name column.
Country/Countries in which the orchestra played as the country column.
Number of concerts in this country as the concerts_no column.
Average rating of the concerts played by this orchestra in this country as the avg_rating column.
Show only the rows of the report for which the orchestra played more than once in a given country.
select o.name, cc.country, cc.concerts_no, cc.avg_rating
from orchestras o
join
(select c.orchestra_id, c.country,
count(c.id) as concerts_no, avg(rating) as avg_rating
from concerts c group by c.country, c.orchestra_id
having count(c.id)>1) as cc on o.id=cc.orchestra_id
group by o.name, cc.country, cc.concerts_no, cc.avg_rating
用两个group by嵌套


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• 这两个关键字并不怎么常用，但是看...所以想弄清楚这两个关键词到底有什么用。 首先是UNION，MSDN上的解释 A union is a user-defined type in which all members share the same memory location.  This means th
这两个关键字并不怎么常用，但是看C++primer plus 面向对象编程部分的时候总是能看到类中有用enum定义的变量。所以想弄清楚这两个关键词到底有什么用。
首先是UNION，MSDN上的解释
A union is a user-defined type in which all members share the same memory location.
This means that at any given time a union can contain no more than one object from its list of members.
It also means that no matter how many members a union has, it always uses only enough memory to store the largest member.
Unions can be useful for conserving memory when you have lots of objects and/or limited memory.
However they require extra care to use correctly because you are responsible for ensuring that you always access the last member that was written to.
If any member types have a non-trivial constructor, then you must write additional code to explicitly construct and destroy that member.
Before using a union, consider whether the problem you are trying to solve could be better expressed by using a base class and derived classes.

可以看到test1.a的值已经丢失了。

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• 它们是位于其表现形式中，或者是在我们的头脑中，还是别的什么地方？我们怎样才能知道它们呢？ 　 　The ancient Greek philosophers took such questions very seriously. Indeed, many of their general ...
• 只用tf-idf的时候输出的结果基本正确，了倒排表优化后输出的答案就完全不正确了。不知道哪里出问题了，求大神解答  # 分数（5） import json from collections import Counter import matplotlib.pyplot ...
• or you may have read about some of its uses but don't realise how many things you can actually do with it. 你可能疑惑.htaccess到底能做些什么，或者你可能曾知道它的一些功能但并不真正了解你实际到底...
• 这条语句什么时候被执行，我说第一次调用foo时，只执行一次；</li><li> <p>struct S{char a;int b}; sizeof(struct S)是多少？我说8；为什么？字节对齐，为了提高访问...
• 现在主要想找出代码哪里有问题，为什么时候对列的确定出问题，代码后附上我的测试文件、用例以及出错的地方。 输入文件名处代码的逻辑还有些问题，但暂时先不管。 代码如下：  #define _CRT_SECURE_NO_...
• 无论用什么能源，将来的汽车都将依然是城市交通拥挤的主要问题。对这个问题提出的一个解决办法就是自动公路系统。 当汽车进入公路系统，一支伸缩臂从车上落下与铁轨接触，这种铁轨同给地下列车供电的铁轨相似。...
• 最近我做的SSH项目，...信息: The Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: G:\Program Files\Genuitec\Common\binary\...
• However, in development, if you want to rewrite a function, other functions must be kept consistent, so it is necessary to update the code or something, which takes lots of time. </li><li> <p>The ...
• //现在从GPS提供商获得值给locManager，发给parameters告诉什么时候更新】 if(isGPSEnabled){ locManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, MIN_TIME_BTWN_UPDATE, MIN_DISTANCE_BTWN_...
• <div><h3>目前遇到的最大的问题，是跨项目依赖，据说1.2.0会支持这个功能； <p><strong>还有很多...我要date_format,将你们的yyyyMMdd 转为yyyy-MM-dd，这对于数据库来说是会消耗性能的。 ...
• 究竟是为什么呢。再次来到json的目录下，再次看有没有把那两个宏开关给关闭？ 嗯哼？ 竟然没有关闭？ 分析？明白了。原来是我把配置和编译同时执行了。这个宏开关是./configure ...生成的。 那么就只好，这样。把./...
• 23.select,selectFrame,selectWindow,selectPopUp，这几个功能的用法，以及在什么时候用？ select用来操作下拉框。语法：select(selectLocator,optionLocator) ,例：select id=person_person_type,lable=非户籍人口...
• 上线编译的时候用的编译机不是自己的机器，而无法部署 FIS 编译环境啊。这时候怎么办呢？ 首先，我们得了解一下 NPM 安装的时候的一些处理。不才，直接贴 NPM 的文档。 <pre><code> ...
• This allows you to build a more advanced test set execution flow, in which you can filter tests in a test set during execution, based on the status or type of each test. VAPI-XP is also fully ...
• By default, Tomcat expects the keystore file to be named .keystore in the user home directory under which Tomcat is running (which may or may not be the same as yours :-). If the keystore file is ...
• 我在sysbench进行otlp.lua进行性能测试的时候，发现一个备机几点挂掉，前面sysbench准备数据是ok的，但是连接测试时出现备机节点mysql挂掉。 [root tools]# ps -ef |grep phxsql root 41128 1 ...