With [tag:LINQ] I would

    var top5 = array.Take(5);

How to do this with Python?

How to take the first N items from a generator or list?

I have a table with columns `name`, `qty`, `rate`. Now I need to add a new column `COLNew` in between the `name` and `qty` columns. How do I add a new column in between two columns?

Insert new column into table in sqlite?

I would like to have a single template that once and for all takes care of pretty-printing all STL containers via `operator&lt;&lt;`. In pseudo code, I&#39;m looking for something like this:

    template&lt;container C, class T, String delim = &quot;, &quot;, String open = &quot;[&quot;, String close = &quot;]&quot;&gt;
    std::ostream &amp; operator&lt;&lt;(std::ostream &amp; o, const C&lt;T&gt; &amp; x)
    {
        o &lt;&lt; open;
        // for (typename C::const_iterator i = x.begin(); i != x.end(); i++) /* Old-school */
        for (auto i = x.begin(); i != x.end(); i++)
        {
            if (i != x.begin()) o &lt;&lt; delim;
            o &lt;&lt; *i;
        }
        o &lt;&lt; close;
        return o;
    }

Now I&#39;ve seen plenty of template magic here on SO that I never thought possible, so I&#39;m wondering if anyone can suggest something that would match all containers `C&lt;T&gt;`. Maybe something trait-ish that can figure out if something has the necessary iterator?



Pretty-print C++ STL containers

I would like to have a single template that once and for all takes care of pretty-printing all STL containers via <code>operator&#x3C;&#x3C;</code>. In pseudo code, I'm looking for something like this:
<pre><code class="hljs language-arduino">template&#x3C;container C, class T, String delim = ", ", String open = "[", String close = "]">
std::ostream &#x26; operator&#x3C;&#x3C;(std::ostream &#x26; o, const C&#x3C;T> &#x26; x)
{
 o &#x3C;&#x3C; open;
 // for (typename C::const_iterator i = x.begin(); i != x.end(); i++) /* Old-school */
 for (auto i = x.begin(); i != x.end(); i++)
 {
 if (i != x.begin()) o &#x3C;&#x3C; delim;
 o &#x3C;&#x3C; *i;
 }
 o &#x3C;&#x3C; close;
 return o;
}
</code></pre>
Now I've seen plenty of template magic here on SO that I never thought possible, so I'm wondering if anyone can suggest something that would match all containers <code>C&#x3C;T></code>. Maybe something trait-ish that can figure out if something has the necessary iterator?

It&#39;s really a simple problem : 

I&#39;m programming a Go program. Should I represent the board with a `QVector&lt;int&gt;` or a `QVector&lt;Player&gt;` where

    enum Player
    {
        EMPTY = 0,
        BLACK = 1,
        WHITE = 2
    };

I guess that of course, using Player instead of integers will be slower. But I wonder how much more, because I believe that using `enum` is better coding.

I&#39;ve done a few tests regarding assigning and comparing Players (as opposed to `int`)

    QVector&lt;int&gt; vec;
    vec.resize(10000000);
    int size = vec.size();


    for(int i =0; i&lt;size; ++i)
    {
        vec[i] = 0;
    }


    for(int i =0; i&lt;size; ++i)
    {
        bool b = (vec[i] == 1);
    }


    QVector&lt;Player&gt; vec2;
    vec2.resize(10000000);
    int size = vec2.size();


    for(int i =0; i&lt;size; ++i)
    {
        vec2[i] = EMPTY;
    }


    for(int i =0; i&lt;size; ++i)
    {
        bool b = (vec2[i] == BLACK);
    }

Basically, it&#39;s only 10% slower. Is there anything else I should know before continuing?

Thanks!

Edit : The 10% difference is not a figment of my imagination, it seems to be specific to Qt and QVector. When I use std::vector, the speed is the same

Are C++ enums slower to use than integers?

Question is in the title really; I&#39;m sure there is something logical, but for now I&#39;m stumped!

Why are bitwise shifts (&lt;&lt; and &gt;&gt;) used for cout and cin?

    class Address {
          int i ;
          char b;
          string c;
          public:
               void showMap ( void ) ;
    };

    void Address :: showMap ( void ) {
                cout &lt;&lt; &quot;address of int    :&quot; &lt;&lt; &amp;i &lt;&lt; endl ;
                cout &lt;&lt; &quot;address of char   :&quot; &lt;&lt; &amp;b &lt;&lt; endl ;
                cout &lt;&lt; &quot;address of string :&quot; &lt;&lt; &amp;c &lt;&lt; endl ;
    }

The output is:

             address of int    :  something
             address of char   :     // nothing, blank area, that is nothing displayed
             address of string :  something 
        

**Why?**

Another interesting thing: if int, char, string is in public, then the output is

      ... int    :  something 
      ... char   :   
      ... string :  something_2

`something_2 - something` is always equal to 8. **Why? (not 9)**

Why is address of char data not displayed?

While reading the documentation for boost::test, I came across the term &quot;free function&quot;. What I understand is that a free function is any function that doesn&#39;t return anything (Its return type is void). But after reading further it seems that free functions also don&#39;t take any arguments. But I am not sure. These all are my assumptions. So could anybody define free function?

What is the meaning of the term &quot;free function&quot; in C++?

Does anybody have an idea how to statically compile any resource file right into the executable or the shared library file using GCC?

For example I&#39;d like to add image files that never change (and if they do, I&#39;d have to replace the file anyway) and wouldn&#39;t want them to lie around in the file system.

If this is possible (and I think it is because Visual C++ for Windows can do this, too), how can I load the files which are stored in the own binary? Does the executable parse itself, find the file and extract the data out of it?

Maybe there&#39;s an option for GCC which I haven&#39;t seen yet. Using search engines didn&#39;t really spit out the right stuff.

I would need this to work for shared libraries and normal ELF-executables.

C/C++ with GCC: Statically add resource files to executable/library

I have the following Jinja template: 

    {% set mybool = False %}
	{% for thing in things %}
		&lt;div class=&#39;indent1&#39;&gt;
            &lt;ul&gt;
	            {% if current_user %}
	              {% if current_user.username == thing[&#39;created_by&#39;][&#39;username&#39;] %}
				    {% set mybool = True %}
					&lt;li&gt;mybool: {{ mybool }}&lt;/li&gt; &lt;!-- prints True --&gt;
	                &lt;li&gt;&lt;a href=&#39;#&#39;&gt;Edit&lt;/a&gt;&lt;/li&gt;
	              {% endif %}
	            {% endif %}
	            &lt;li&gt;Flag&lt;/li&gt;
	        &lt;/ul&gt;
        &lt;/div&gt;
		&lt;hr /&gt;
	{% endfor %}
	
	{% if not mybool %}
        &lt;!-- always prints this --&gt;
        &lt;p&gt;mybool is false!&lt;/p&gt;
	{% else %}
	  &lt;p&gt;mybool is true!&lt;/p&gt;
	{% endif %}

If the condition is met in the `for` loop, I&#39;d like to change `mybool` to true so I can display `mybool is true!` below. However, it looks like the scope of the inner `mybool` is limited to the `if` statement, so the *desired* `mybool` is never set. 

How can I set the &quot;global&quot; `mybool` so I can use it in the last `if` statement? 

**EDIT**

I&#39;ve found [some suggestions][1] (only the cached page views correctly), but they don&#39;t seem to work. Perhaps they&#39;re deprecated in Jinja2...

**EDIT**

Solution provided below. I am still curious why the suggestions above do not work though. Does anyone know for sure that they were deprecated? 

  [1]: http://webcache.googleusercontent.com/search?q=cache:BCRT8FHONykJ:svn.python.org/projects/external/Jinja-1.2/docs/html/scopes.html+jinja+top+level+variable&amp;hl=en&amp;gl=us&amp;strip=0

Can a Jinja variable&#39;s scope extend beyond in an inner block?

I just stumbled upon something I&#39;ve never seen before. In the source of Backbone.js&#39;s example TODO application ([Backbone TODO Example][1]) they had their templates inside a `&lt;script type = &quot;text/template&quot;&gt;&lt;/script&gt;`, which contained code that looks like something out of PHP but with JavaScript tags.

Can someone explain this to me? Is this legit?


  [1]: http://documentcloud.github.com/backbone/examples/todos/index.html

Explanation of &lt;script type = &quot;text/template&quot;&gt; ... &lt;/script&gt;

I have a template function with one argument.
I have to instantiate that function without calling that function means explicitly I have to instantiate.

I have this function:

    template &lt;class T&gt; int function_name(T a) {}

I instantiated that function like this:

    template int function_name&lt;int&gt;(int);

But I got the following errors:

    error: expected primary-expression before &#39;template&#39;
    error: expected `;&#39; before &#39;template&#39;


How do I explicitly instantiate a template function?

I don&#39;t get it, it seems to me that the call to `f` is completely unambiguous, but it fails to compile with `expected primary-expression before ‘int’`. If I comment out the line with the call to `f`, it compiles fine.

    template&lt;typename T&gt;
    struct A {
        template&lt;typename S&gt;
        void f() { }
    };

    template&lt;typename T&gt;
    struct B : A&lt;T&gt; {
        void g() {
            this-&gt;f&lt;int&gt;();
        }
    };

Why do I get an error trying to call a template member function with an explicit type parameter?

this is my code :

    {% for i,j in enumerate(a) %}
    	{{i}} ,{{j}}
    {% endfor%}

but , it show a error , i think it cant run the `enumerate` method ,

so how to run the `enumerate`  in django template ,

thanks

how to run this code in django template 

I guess not, but I would like to confirm. Is there any use for `const Foo&amp;&amp;`, where `Foo` is a class type?

Do rvalue references to const have any use?

For the following code:

    struct B
    {
        void g()
        {
            []() { B::f(); }();
        }
    
        static void f();
    };

g++ 4.6 gives the error:

&gt; test.cpp: In lambda function:  
&gt;  test.cpp:44:21: error: &#39;this&#39; was not captured for this lambda function

(Interestingly, g++ 4.5 compiles the code fine).

Is this a bug in g++ 4.6, or is it really necessary to capture the &#39;this&#39; parameter to be able to call a static member function? I don&#39;t see why it should be, I even qualified the call with `B::`.

lambdas require capturing &#39;this&#39; to call static member function?

I am reading Scott Meyers &quot;Effective C++&quot; book. It was mentioned that there are `tr1::shared_ptr` and `tr1::weak_ptr` act like built-in pointers, but they keep track of how many `tr1::shared_ptrs` point to an object.  

This is known as reference counting. This works well in preventing resource leaks in acyclic data structures, but if two or more objects contain `tr1::shared_ptrs` such that a cycle is formed, the cycle may keep each other&#39;s reference count above zero, even when all external pointers to the cycle have been destroyed.  

That&#39;s where `tr1::weak_ptrs` come in.

My question is how cyclic data structures make the reference count above zero. I kindly request an example C++ program. How is the problem solved by `weak_ptrs`? (again, with example please).

shared_ptr and weak_ptr differences

I&#39;m trying to understand rvalue references and move semantics of C++11.

What is the difference between these examples, and which of them is going to do no vector copy?

## First example ##
    std::vector&lt;int&gt; return_vector(void)
    {
        std::vector&lt;int&gt; tmp {1,2,3,4,5};
        return tmp;
    }
    
    std::vector&lt;int&gt; &amp;&amp;rval_ref = return_vector();

## Second example ##
    std::vector&lt;int&gt;&amp;&amp; return_vector(void)
    {
        std::vector&lt;int&gt; tmp {1,2,3,4,5};
        return std::move(tmp);
    }
    
    std::vector&lt;int&gt; &amp;&amp;rval_ref = return_vector();

## Third example ##
    std::vector&lt;int&gt; return_vector(void)
    {
        std::vector&lt;int&gt; tmp {1,2,3,4,5};
        return std::move(tmp);
    }
    
    std::vector&lt;int&gt; &amp;&amp;rval_ref = return_vector();


C++11 rvalues and move semantics confusion (return statement)

Is there a way to detect at compile-time if the compiler supports certain features of C++11?  For example, something like this:

    #ifndef VARIADIC_TEMPLATES_SUPPORTED

    #error &quot;Your compiler doesn&#39;t support variadic templates.  :(&quot;

    #else

    template &lt;typename... DatatypeList&gt;
    class Tuple
    {
        // ...
    }

    #endif

How do I check for C++11 support?

I see questions on SO every so often about overloading the comma operator in C++ (mainly unrelated to the overloading itself, but things like the notion of sequence points), and it makes me wonder:

When *should* you overload the comma? What are some examples of its practical uses?

I just can&#39;t think of any examples off the top of my head where I&#39;ve seen or needed to something like

    foo, bar;

in real-world code, so I&#39;m curious as to when (if ever) this is actually used.

When to Overload the Comma Operator?

Consider the following program:

    struct ghost
    {
        // ghosts like to pretend that they don&#39;t exist
        ghost* operator&amp;() const volatile { return 0; }
    };

    int main()
    {
        ghost clyde;
        ghost* clydes_address = &amp;clyde; // darn; that&#39;s not clyde&#39;s address :&#39;( 
    }

How do I get `clyde`&#39;s address?

I&#39;m looking for a solution that will work equally well for all types of objects.  A C++03 solution would be nice, but I&#39;m interested in C++11 solutions too.  If possible, let&#39;s avoid any implementation-specific behavior.

I am aware of C++11&#39;s `std::addressof` function template, but am not interested in using it here:  I&#39;d like to understand how a Standard Library implementor might implement this function template.

How can I reliably get an object&#39;s address when operator&amp; is overloaded?

Okay, I&#39;ve been [inspired to do some head punching](https://stackoverflow.com/q/6494591/82320). Seems like overloading `operator&amp;` leads to not a small amount of pain.

What legitimate cases exist for overloading it?

(Can&#39;t say I&#39;ve ever done that....)

What legitimate reasons exist to overload the unary operator&amp;?

I am trying to do operator overloads for `+=`, but I can&#39;t. I can only make an operator overload for `+`.

How come?


**Edit**

The reason this is not working is that I have a Vector class (with an X and Y field). Consider the following example.

    vector1 += vector2;

If my operator overload is set to:

    public static Vector operator +(Vector left, Vector right)
    {
        return new Vector(right.x + left.x, right.y + left.y);
    }

Then the result won&#39;t be added to vector1, but instead, vector1 will become a brand new Vector by reference as well.

C# operator overload for `+=`?

Is it possible to overload `[]` operator twice? To allow, something like this: `function[3][3]`(like in a two dimensional array). 

If it is possible, I would like to see some example code.

Operator[][] overload

When using Express for Node.js, I noticed that it outputs the HTML code without any newline characters or tabs. Though it may be more efficient to download, it&#39;s not very readable during development.

How can I get Express to output nicely formatted HTML?

How can I get Express to output nicely formatted HTML?

I&#39;m building a PHP script that feeds JSON data to another script. My script builds data into a large associative array, and then outputs the data using `json_encode`. Here is an example script:

    $data = array(&#39;a&#39; =&gt; &#39;apple&#39;, &#39;b&#39; =&gt; &#39;banana&#39;, &#39;c&#39; =&gt; &#39;catnip&#39;);
    header(&#39;Content-type: text/javascript&#39;);
    echo json_encode($data);

The above code yields the following output:

    {&quot;a&quot;:&quot;apple&quot;,&quot;b&quot;:&quot;banana&quot;,&quot;c&quot;:&quot;catnip&quot;}

This is great if you have a small amount of data, but I&#39;d prefer something along these lines: 

    {
        &quot;a&quot;: &quot;apple&quot;,
        &quot;b&quot;: &quot;banana&quot;,
        &quot;c&quot;: &quot;catnip&quot;
    }

Is there a way to do this in PHP without an ugly hack? It seems like someone at [Facebook][1] figured it out.


  [1]: https://graph.facebook.com/19292868552

Pretty-Printing JSON with PHP

I am using [lxml.html][1] to generate some HTML. I want to pretty print (with indentation) my final result into an html file. How do I do that?

This is what I have tried and got till now
    

    import lxml.html as lh
    from lxml.html import builder as E
    sliderRoot=lh.Element(&quot;div&quot;, E.CLASS(&quot;scroll&quot;), style=&quot;overflow-x: hidden; overflow-y: hidden;&quot;)
    scrollContainer=lh.Element(&quot;div&quot;, E.CLASS(&quot;scrollContainer&quot;), style=&quot;width: 4340px;&quot;)
    sliderRoot.append(scrollContainer)
    print lh.tostring(sliderRoot, pretty_print = True, method=&quot;html&quot;)

As you can see I am using the `pretty_print=True` attribute. I thought that would give indented code, but it doesn&#39;t really help. This is the output :

`&lt;div style=&quot;overflow-x: hidden; overflow-y: hidden;&quot; class=&quot;scroll&quot;&gt;&lt;div style=&quot;width: 4340px;&quot; class=&quot;scrollContainer&quot;&gt;&lt;/div&gt;&lt;/div&gt;`


  [1]: http://lxml.de/lxmlhtml.html

How to Pretty Print HTML to a file, with indentation

I have a compact JSON string, and I want to format it nicely in Java without having to deserialize it first -- e.g. just like [jsonlint.org][1] does it.  Are there any libraries out there that provides this?

A similar solution for XML would also be nice.


  [1]: http://jsonlint.org


How do I pretty-print existing JSON data with Java?

I have a text box and I want to display a C# object in it in a human-readable way, just for debugging reasons. I don&#39;t want to use external libraries if possible. How do I do this?

Pretty-print C++ STL containers

C++ Problem Overview

C++ Solutions

Insert new column into table in sqlite?

How to take the first N items from a generator or list?

Attributions