You need extra brackets, until [c++14 proposal][1] kicks in.

    std::array&lt;std::array&lt;int, 3&gt;, 3&gt; arr = {{{5, 8, 2}, {8, 3, 1}, {5, 3, 9}}};


  [1]: http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2013/n3526.html

I have some confusion regarding meta-classes.

###With inheritance

    class AttributeInitType(object):

       def __init__(self,**kwargs):
           for name, value in kwargs.items():
              setattr(self, name, value)

    class Car(AttributeInitType):

        def __init__(self,**kwargs):
            super(Car, self).__init__(**kwargs)
        @property
        def description(self):
           return &quot;%s %s %s %s&quot; % (self.color, self.year, self.make, self.model)

    c = Car(make=&#39;Toyota&#39;, model=&#39;Prius&#39;, year=2005, color=&#39;green&#39;)
    print c.description

###With meta class

    class AttributeInitType(type):
       def __call__(self, *args, **kwargs):
           obj = type.__call__(self, *args)
           for name, value in kwargs.items():
               setattr(obj, name, value)
           return obj

    class Car(object):
       __metaclass__ = AttributeInitType

       @property
       def description(self):
           return &quot;%s %s %s %s&quot; % (self.color, self.year, self.make, self.model)


    c = Car(make=&#39;Toyota&#39;, model=&#39;Prius&#39;, year=2005,color=&#39;blue&#39;)
    print c.description

As above example is not useful as practically but just for understanding,

I have some questions Like,


1. What is the difference/similarity between a meta class and inheritance?

2. Where should one use a meta class or inheritance?


Understanding metaclass and inheritance in Python

I have a `UIImageView` on each of my `UITableView` cells, that display a remote image (using `SDWebImage`). I&#39;ve done some `QuartzCore` layer styling to the image view, as such:

    UIImageView *itemImageView = (UIImageView *)[cell viewWithTag:100];
        itemImageView.layer.borderWidth = 1.0f;
        itemImageView.layer.borderColor = [UIColor concreteColor].CGColor;
        itemImageView.layer.masksToBounds = NO;
        itemImageView.clipsToBounds = YES;

So now I have a 50x50 square with a faint grey border, but I&#39;d like to make it circular instead of squared. The app `Hemoglobe` uses circular images in table views, and that&#39;s the effect I&#39;d like to achieve. However, I don&#39;t want to use `cornerRadius`, as that degrades my scrolling FPS. 

Here&#39;s `Hemoglobe` showing circular `UIImageViews`: 

![enter image description here][1]

Is there any way to get this effect? Thanks.

  [1]: http://i.stack.imgur.com/TOh0K.jpg

Circular UIImageView in UITableView without performance hit?

In C++, how do I create a multidimensional `std::array`? I&#39;ve tried this:

    std::array&lt;std::array&lt;int, 3&gt;, 3&gt; arr = {{5, 8, 2}, {8, 3, 1}, {5, 3, 9}};
But it doesn&#39;t work. What am I doing wrong and how do I fix this?

Multidimensional std::array

In C++, how do I create a multidimensional <code>std::array</code>? I've tried this:
<pre><code class="hljs language-c">std::array&#x3C;std::array&#x3C;int, 3>, 3> arr = {{5, 8, 2}, {8, 3, 1}, {5, 3, 9}};
</code></pre>
But it doesn't work. What am I doing wrong and how do I fix this?

I&#39;m trying to send value into function using reference pointer but it gave me a completely non-obvious error

    #include &quot;stdafx.h&quot;
    #include &lt;iostream&gt;
    
    using namespace std;
    
    void test(float *&amp;x){
    	
    	*x = 1000;
    }
    
    int main(){
    	float nKByte = 100.0;
    	test(&amp;nKByte);
    	cout &lt;&lt; nKByte &lt;&lt; &quot; megabytes&quot; &lt;&lt; endl;
    	cin.get();
    }

&gt; Error : initial value of reference to non-const must be an lvalue

I have no idea what I must do to repair above code, can someone give me some ideas on how to fix that code?

initial value of reference to non-const must be an lvalue

Is it safe to check a pointer to not being `NULL` by writing simply `if(pointer)` or do I have to use `if(pointer != NULL)`?

Can I use if (pointer) instead of if (pointer != NULL)?

I&#39;m writing an accessor method for a shared pointer in C++ that goes something like this:

    class Foo {
    public:
        return_type getBar() const {
            return m_bar;
        }

    private:
        boost::shared_ptr&lt;Bar&gt; m_bar;
    }

So to support the const-ness of `getBar()` the return type should be a `boost::shared_ptr` that prevents modification of the `Bar` it points to. My _guess_ is that `shared_ptr&lt;const Bar&gt;` is the type I want to return to do that, whereas `const shared_ptr&lt;Bar&gt;` would prevent reassignment of the pointer itself to point to a different `Bar` but allow modification of the `Bar` that it points to...  However, I&#39;m not sure. I&#39;d appreciate it if someone who knows for sure could either confirm this, or correct me if I got it wrong. Thanks!

Difference between `const shared_ptr&lt;T&gt;` and `shared_ptr&lt;const T&gt;`?

Item 18 of Scott Meyers&#39;s book *Effective STL: 50 Specific Ways to Improve Your Use of the Standard Template Library* says to avoid `vector &lt;bool&gt;` as it&#39;s not an STL container and it doesn&#39;t really hold `bool`s.

The following code:

    vector &lt;bool&gt; v; 
    bool *pb =&amp;v[0];
will not compile, violating a requirement of STL containers.

Error:

    cannot convert &#39;std::vector&lt;bool&gt;::reference* {aka std::_Bit_reference*}&#39; to &#39;bool*&#39; in initialization

`vector&lt;T&gt;::operator []` return type is supposed to be `T&amp;`, but why is it a special case for `vector&lt;bool&gt;`?

What does `vector&lt;bool&gt;` really consist of?

The Item further says:

    deque&lt;bool&gt; v; // is a STL container and it really contains bools

Can this be used as an alternative to `vector&lt;bool&gt;`?

Can anyone please explain this?




Why isn&#39;t vector&lt;bool&gt; a STL container?

I have long assumed that for any empty `std::vector` *V*, `V.begin() == V.end()`. Yet I see nothing in the C++ specification that states this to *always* be true. Is it necessarily true or does it just happen to be true on most implementations?

Is begin() == end() for any empty() vector?

C++98 has `front_inserter`, `back_inserter`, and `inserter`, but there don&#39;t seem to be any emplacement versions of these in C++11 or draft C++14. Is there any technical reason we couldn&#39;t have `front_emplacer`, `back_emplacer`, and `emplacer`?


Why no emplacement iterators in C++11 or C++14?

I use the following code to test the C++ `&lt;random&gt;` library.

Why do I get the exact same sequence for every run of the compiled executable? Is `rd()` deterministic upon compilation? How do I get different output for each run?

GCC 4.8.1 on Windows 7 64bit. Using MinGW distribution from [http://nuwen.net/mingw.html][1].

**EDIT:** I tested the same piece code with Visual Studio. There is no problem. The outputs are non deterministic. This could be a bug in mingw gcc 4.8.1 that I used.

    #include &lt;iostream&gt;
    #include &lt;random&gt;
    using namespace std;

    int main(){
     random_device rd;
     mt19937 mt(rd());
     uniform_int_distribution&lt;int&gt; dist(0,99);
     for (int i = 0; i&lt; 16; ++i){
        cout&lt;&lt;dist(mt)&lt;&lt;&quot; &quot;;
     }
     cout &lt;&lt;endl;
    }


  [1]: http://nuwen.net/mingw.html

Why do I get the same sequence for every run with std::random_device with mingw gcc4.8.1?

Everyone creates `std::vector` from `std::initializer_list`, but what about the other way around?

eg. if you use a `std::initializer_list` as a parameter:

    void someThing(std::initializer_list&lt;int&gt; items)
    {
    ...
    }

There are times when you have your items in a `vector&lt;T&gt;` instead of a literal list:

    std::vector&lt;int&gt; v;
    // populate v with values
    someThing(v); // boom! No viable conversion etc.

The more general question is: how to create an `stl::initializer_list` from a STL iterable, not just `std::vector`.

Convert a vector&lt;T&gt; to initializer_list&lt;T&gt;

I am using 

    unordered_map&lt;string, int&gt;

and 

    unordered_map&lt;int, int&gt;

What hash function is used in each case and what is chance of collision in each case?
I will be inserting unique string and unique int as keys in each case respectively.

I am interested in knowing the algorithm of hash function in case of string and int keys and their collision stats.

Content Type	Original Author	Original Content on Stackoverflow
Question	LazySloth13	View Question on Stackoverflow
Solution 1 - C++	billz	View Answer on Stackoverflow

Multidimensional std::array

C++ Problem Overview

C++ Solutions

Solution 1 - C++

Circular UIImageView in UITableView without performance hit?

Understanding metaclass and inheritance in Python

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