There are no differences between structs and classes in this regard in C++. They all are called just *class types*.

Members of class types have no default values in general case. In order to for a class member to get a deterministic value it has to be *initialized*, which can be done by

* Default constructor of the member itself
* Constructor initializer list of the enclosing class
* Explicitly specified initializer for object of the enclosing class (that includes value-initialization and initialization with aggregate initializer).

Additionally, all objects with static storage duration are zero-initialized at the program startup.

Aside from the above cases, class members, once again, have no default values and will initially contain unpredictable garbage values.

Yeah, there is one.  If you initialize an object with the default constructor and use parentheses then the POD members will be zero initialized:

    someClass * p = new someClass();



I have a jQuery script that adds a new field to a form, and this field contains dynamic information from an array. The problem is that I can&#39;t figure out how to add an array.each to populate the options of the select field within the javascript without breaking the HAML indentation and causing errors.

Here is my best attempt that does not work:

    %script(type=&quot;text/javascript&quot;)  
      $(&#39;#mylink&#39;).click(function() {  
      $(&#39;#mylink&#39;).after(&#39;&lt;select&gt;  
      - myarray.each do |options|  
         &lt;option value=&quot;#{options.id}&quot;&gt;#{options.name}&lt;/option&gt;  
      &lt;/select&gt;);  
      )};

Also tried it with the :javascript filter with no luck.

Ruby methods within Javascript within HAML

From what I understand, `super` keyword invokes a method with the same name as the current method in the superclass of the current class. Below in the `autoload` method, there is a call to `super`. I would like to know in which superclass I would find a method with the same name or what does the call to `super` do here

    module ActiveSupport
      module Autoload
        ...      
        def autoload(const_name, path = @@at_path)
          full = [self.name, @@under_path, const_name.to_s, path].compact.join(&quot;::&quot;)
          location = path || Inflector.underscore(full)
    
          if @@eager_autoload
            @@autoloads[const_name] = location
          end
          super const_name, location
        end
       .... 
      end
    end

    module ActiveRecord
      extend ActiveSupport::Autoload
      ...
      autoload :TestCase
      autoload :TestFixtures, &#39;active_record/fixtures&#39;
    end

This code is from the rails master branch. Thanks much.

ruby super keyword

What is the default values for members of a struct and members of a class in c++, and how do these rules differ (e.g. between classes/structs/primitives/etc) ? Are there circumstances where the rules about the default values differs ?

What is the default value for C++ class members

<p>What is the default values for members of a struct and members of a class in c++, and how do these rules differ (e.g. between classes/structs/primitives/etc) ? Are there circumstances where the rules about the default values differs ?</p>


For example result of this code snippet depends on which machine: the compiler machine or the machine executable file works?

    sizeof(short int)



Is sizeof in C++ evaluated at compilation time or run time?

I need to parse a URL to get the protocol, host, path, and query in an application I am writing in C++. The application is intended to be cross-platform. I&#39;m surprised I can&#39;t find anything that does this in the [boost][1] or [POCO][2] libraries. Is it somewhere obvious I&#39;m not looking? Any suggestions on appropriate open source libs? Or is this something I just have to do my self? It&#39;s not super complicated but it seems like such a common task I am surprised there isn&#39;t a common solution. 


  [1]: http://www.boost.org/
  [2]: http://pocoproject.org/

Easy way to parse a url in C++ cross platform?

How do I print coloured characters to a Linux terminal that supports it?

How do I tell whether the terminal supports colour codes?


How do I output coloured text to a Linux terminal?

I want to &quot;stringify&quot; a number and add zero-padding, like how `printf(&quot;%05d&quot;)` would add leading zeros if the number is less than 5 digits.


Convert an int to a QString with zero padding (leading zeroes)

I am trying to change the default order of the items in a set of integers to be lexicographic instead of numeric, and I can&#39;t get the following to compile with g++:

file.cpp:

    bool lex_compare(const int64_t &amp;a, const int64_t &amp;b) 
    {
    	stringstream s1,s2;
    	s1 &lt;&lt; a;
    	s2 &lt;&lt; b;
    	return s1.str() &lt; s2.str();
    }
    
    void foo()
    {
    	set&lt;int64_t, lex_compare&gt; s;
    	s.insert(1);
        ...
    }

I get the following error:

    error: type/value mismatch at argument 2 in template parameter list for ‘template&lt;class _Key, class _Compare, class _Alloc&gt; class std::set’
    error:   expected a type, got ‘lex_compare’

what am I doing wrong?


Using custom std::set comparator

I&#39;m trying to use the `.Contains()` function on a list of custom objects

This is the list:

    List&lt;CartProduct&gt; CartProducts = new List&lt;CartProduct&gt;();

And the `CartProduct`:

    public class CartProduct
    {
        public Int32 ID;
        public String Name;
        public Int32 Number;
        public Decimal CurrentPrice;
        /// &lt;summary&gt;
        /// 
        /// &lt;/summary&gt;
        /// &lt;param name=&quot;ID&quot;&gt;The ID of the product&lt;/param&gt;
        /// &lt;param name=&quot;Name&quot;&gt;The name of the product&lt;/param&gt;
        /// &lt;param name=&quot;Number&quot;&gt;The total number of that product&lt;/param&gt;
        /// &lt;param name=&quot;CurrentPrice&quot;&gt;The currentprice for the product (1 piece)&lt;/param&gt;
        public CartProduct(Int32 ID, String Name, Int32 Number, Decimal CurrentPrice)
        {
            this.ID = ID;
            this.Name = Name;
            this.Number = Number;
            this.CurrentPrice = CurrentPrice;
        }
        public String ToString()
        {
            return Name;
        }
    }

So i try to find a similar cartproduct within the list:

    if (CartProducts.Contains(p))

But it ignores similar cartproducts and i don&#39;t seem to know what it checks on - the ID? or it all?

Thanks in advance! :)

.Contains() on a list of custom class objects

Given:

    case class FirstCC {
      def name: String = ... // something that will give &quot;FirstCC&quot;
    }
    case class SecondCC extends FirstCC
    val one = FirstCC()
    val two = SecondCC()

How can I get `&quot;FirstCC&quot;` from `one.name` and `&quot;SecondCC&quot;` from `two.name`?


How can I easily get a Scala case class&#39;s name?

Is there a way to grab a list of attributes that exist on instances of a class?

    class new_class():
        def __init__(self, number):
            self.multi = int(number) * 2
            self.str = str(number)
    
    a = new_class(2)
    print(&#39;, &#39;.join(a.SOMETHING))

The desired result is that &quot;multi, str&quot; will be output.  I want this to see the current attributes from various parts of a script.

List attributes of an object

Should I give my class members default values like this:

    class Foo:
        num = 1

or like this?

    class Foo:
        def __init__(self):
            self.num = 1

In [this question][1] I discovered that in both cases,

    bar = Foo()
    bar.num += 1

is a well-defined operation.

I understand that the first method will give me a class variable while the second one will not. However, if I do not require a class variable, but only need to set a default value for my instance variables, are both methods equally good? Or one of them more &#39;pythonic&#39; than the other?

One thing I&#39;ve noticed is that in the Django tutorial, [they use the second method to declare Models.][2] Personally I think the second method is more elegant, but I&#39;d like to know what the &#39;standard&#39; way is.

[2]: http://docs.djangoproject.com/en/dev/intro/tutorial01/#id3

[1]: https://stackoverflow.com/questions/2424451/about-python-class-and-instance-variables

How should I declare default values for instance variables in Python?

What is the purpose of the `self` word in Python? I understand it refers to the specific object instance created from that class. But why does it explicitly need to be added to every function as a parameter? To illustrate, in Ruby I can do this:

```ruby
class MyClass
    def func(name)
        @name = name
    end
end
```

However, in Python I need to include `self`:

```python
class MyClass:
    def func(self, name):
        self.name = name
```

What is the purpose of the word &#39;self&#39;?

I&#39;ve been reading about OOP in C but I never liked how you can&#39;t have private data members like you can in C++. But then it came to my mind that you could create 2 structures. One is defined in the header file and the other is defined in the source file.

    // =========================================
    // in somestruct.h
    typedef struct {
      int _public_member;
    } SomeStruct;
                
    // =========================================
    // in somestruct.c

    #include &quot;somestruct.h&quot;

    typedef struct {
      int _public_member;
      int _private_member;
    } SomeStructSource;
            
    SomeStruct *SomeStruct_Create()
    {
      SomeStructSource *p = (SomeStructSource *)malloc(sizeof(SomeStructSource));
      p-&gt;_private_member = 42;
      return (SomeStruct *)p;
    }

From here you can just cast one structure to the other.
Is this considered bad practice? Or is it done often?



Hiding members in a C struct

I&#39;ve seen a lot of questions on this but I&#39;m going to ask the question differently without specific code.  Is there a way of ***EASILY*** determining what is causing the type to be incomplete?  In my case I&#39;m using someone elses code and I&#39;m completely sure I don&#39;t have the headers right, but (since computers do this stuff much faster and better than human eyeballs) is there a way to get the compiler to say, &quot;hey you *think* you have type X at line 34 but that&#39;s actually *missing*.&quot;  The error itself only shows up when you assign, which isn&#39;t very helpful.

dereferencing pointer to incomplete type

I have a C# background. I am very much a newbie to a low-level language like C.

In C#, `struct`&#39;s memory is laid out by the compiler by default. The compiler can re-order data fields or pad additional bits between fields implicitly. So, I had to specify some special attribute to override this behavior for exact layout.

AFAIK, C does not reorder or align memory layout of a `struct` by default. However, I heard there&#39;s a little exception that is very hard to find.

What is C&#39;s memory layout behavior? What should be re-ordered/aligned and not?

Struct memory layout in C

After finishing my C++ class it seemed to me the structs/classes are virtually identical except with a few minor differences.

I&#39;ve never programmed in C before; but I do know that it has structs. In C is it possible to inherit other structs and set a modifier of public/private?

If you can do this in regular C why in the world do we need C++? What makes classes different from a struct?

C/C++ Struct vs Class

I would like to differentiate between following cases:

 1. A plain value type (e.g. `int`)
 2. A nullable value type (e.g. `int?`)
 3. A reference type (e.g. `string`) - optionally, I would not care if this mapped to (1) or (2) above

I have come up with the following code, which works fine for cases (1) and (2):

    static void Foo&lt;T&gt;(T a) where T : struct { } // 1

    static void Foo&lt;T&gt;(T? a) where T : struct { } // 2

However, if I try to detect case (3) like this, it does not compile:

    static void Foo&lt;T&gt;(T a) where T : class { } // 3

The error message is _Type &#39;X&#39; already defines a member called &#39;Foo&#39; with the same parameter types_. Well, somehow I cannot make a difference between `where T : struct` and `where T : class`.

If I remove the third function (3), the following code does not compile either:

    int x = 1;
    int? y = 2;
    string z = &quot;a&quot;;

    Foo (x); // OK, calls (1)
    Foo (y); // OK, calls (2)
    Foo (z); // error: the type &#39;string&#39; must be a non-nullable value type ...

How can I get `Foo(z)` to compile, mapping it to one of the above functions (or a third one with another constraint, which I have not thought of)?

Generic constraints, where T : struct and where T : class

I have an input text :

    &lt;input name=&quot;Email&quot; type=&quot;text&quot; id=&quot;Email&quot; value=&quot;email@abc.com&quot; /&gt;

I want to put a default value like &quot;What&#39;s your programming question ? be specific.&quot; in StackOverFlow, and when the user click on it the default value disapear.



Delete default value of an input text on click

How do I set a default value in Hibernate field?

How to set a default entity property value with Hibernate

When defining an attribute for a custom JSP tag, is it possible to specify a default value? The `attribute` directive doesn&#39;t have a default value attribute. Currently I&#39;m making do with:

    &lt;%@ attribute name=&quot;myAttr&quot; required=&quot;false&quot; type=&quot;java.lang.String&quot; %&gt;
    
    &lt;c:if test=&quot;${empty myAttr}&quot; &gt;
     &lt;c:set var=&quot;myAttr&quot; value=&quot;defaultValue&quot; /&gt;
    &lt;/c:if&gt;

Is there a better way?

Default value on JSP custom-tag attribute

I came across an old table today with a datetime column called &#39;Created&#39; which allows nulls.  Now, I&#39;d want to change this so that it is NOT NULL, and also include a constraint to add in a default value (getdate()).

So far I&#39;ve got the following script, which works fine provided that i&#39;ve cleaned up all the nulls beforehand:

    ALTER TABLE dbo.MyTable ALTER COLUMN Created DATETIME NOT NULL 

Is there any way to also specify the default value as well on the ALTER statement?

Change a Nullable column to NOT NULL with Default Value

I come with this:

&lt;pre&gt;
(defn string-&gt;integer [str &amp; [base]]
  (Integer/parseInt str (if (nil? base) 10 base)))

(string-&gt;integer &quot;10&quot;)
(string-&gt;integer &quot;FF&quot; 16)
&lt;/pre&gt;
But it must be a better way to do this.

Content Type	Original Author	Original Content on Stackoverflow
Question	leeeroy	View Question on Stackoverflow
Solution 1 - C++	AnT	View Answer on Stackoverflow
Solution 2 - C++	Hans Passant	View Answer on Stackoverflow

What is the default value for C++ class members

C++ Problem Overview

C++ Solutions

Solution 1 - C++

Solution 2 - C++

ruby super keyword

Ruby methods within Javascript within HAML

Attributions