What is the best way to initialize a private, static data member in C++?  I tried this in my header file, but it gives me weird linker errors:

    class foo
    {
        private:
            static int i;
    };

    int foo::i = 0;

I&#39;m guessing this is because I can&#39;t initialize a private member from outside the class.  So what&#39;s the best way to do this?

How to initialize private static members in C++?

I want to have a `static const` `char` array in my class. GCC complained and told me I should use `constexpr`, although now it&#39;s telling me it&#39;s an undefined reference. If I make the array a non-member then it compiles. What is going on?

    // .hpp
    struct foo {
      void bar();
      static constexpr char baz[] = &quot;quz&quot;;
    };

    // .cpp
    void foo::bar() {
      std::string str(baz); // undefined reference to baz
    }



Undefined reference to static constexpr char[]

I have this code:

    private static $dates = array(
      &#39;start&#39; =&gt; mktime( 0,  0,  0,  7, 30, 2009),  // Start date
      &#39;end&#39;   =&gt; mktime( 0,  0,  0,  8,  2, 2009),  // End date
      &#39;close&#39; =&gt; mktime(23, 59, 59,  7, 20, 2009),  // Date when registration closes
      &#39;early&#39; =&gt; mktime( 0,  0,  0,  3, 19, 2009),  // Date when early bird discount ends
    );

Which gives me the following error:

&gt;Parse error: syntax error, unexpected &#39;(&#39;, expecting &#39;)&#39; in /home/user/Sites/site/registration/inc/registration.class.inc on line 19

So, I guess I am doing something wrong... but how can I do this if not like that? If I change the mktime stuff with regular strings, it works. So I know that I can do it *sort of* like that..

Anyone have some pointers?

How to initialize static variables

In PHP 5, what is the difference between using `const` and `static`?

When is each appropriate? And what role does `public`, `protected` and `private` play - if any?


PHP 5: const vs static

I am getting an error when trying to compile my code in g++ using the current signature:

    cannot declare member function static void Foo::Bar(std::ostream&amp;, const Foo::Node*) to have static linkage


My question is twofold:

 1. Why does it not Compile this way?
 2. What is the correct signature, and why?


Signatures have always been the death of me when using C++




Edit: Here is the class header file, as well:

    class Foo {


    public:
        Foo();

        ~Foo();

        bool insert(const Foo2 &amp;v);

        Foo * find(const Foo2 &amp;v);

        const Foo * find(const Foo2 &amp;v) const;

        void output(ostream &amp;s) const;

    private:
        //Foo(const Foo &amp;v);
        //Foo&amp; operator =(const Foo &amp;v);
        //Not implemented; unneeded


        struct Node {
            Foo2 info;
            Node *left;
            Node *right;
        };

        Node * root;

        static bool insert(const Foo2 &amp;v, Node *&amp;p);


        static void output(ostream &amp;s, const Node *p);


        static void deleteAll(Node *p);


Static member functions error; How to properly write the signature?

I have the following php. However when I see the index.php I get the following error message. 

&gt; Strict standards: Non-static method
&gt; Page::getInstanceByName() should not
&gt; be called statically in
&gt; /var/www/webworks/index.php on line 12

I am hoping someone can tell me how to fix the problem.

index.php

    // { common variables and functions
    include_once(&#39;ww.incs/common.php&#39;);
    $page=isset($_REQUEST[&#39;page&#39;])?$_REQUEST[&#39;page&#39;]:&#39;&#39;;
    $id=isset($_REQUEST[&#39;id&#39;])?(int)$_REQUEST[&#39;id&#39;]:0;
    ...
    
    // { get current page id
    if(!$id){
    	if($page){ // load by name
    		$r=Page::getInstanceByName($page);
    		if($r &amp;&amp; isset($r-&gt;id))$id=$r-&gt;id;
    	}
    	if(!$id){ // else load by special
    		$special=1;
    		if(!$page){
    			$r=Page::getInstanceBySpecial($special);
    			if($r &amp;&amp; isset($r-&gt;id))$id=$r-&gt;id;
    		}
    	}
    }
    
    // { load page data
    if($id){
    	$PAGEDATA=(isset($r) &amp;&amp; $r)?$r : Page::getInstance($id);
    }
    else{
    	echo &#39;404 thing goes here&#39;;
    	exit;
    }
    ...
    ...


ww.incs/common.php

    &lt;?php
    require dirname(__FILE__).&#39;/basics.php&#39;;
    ...
    ...

ww.incs/basics.php

    session_start();
    if(!function_exists(&#39;__autoload&#39;)){
    	function __autoload($name) {
    		require $name . &#39;.php&#39;;
    	}
    }
    ...
    ...


Page.php

    class Page{
    	static $instances			  = array();
    	static $instancesByName		= array();
    	static $instancesBySpecial	 = array();
    	function __construct($v,$byField=0,$fromRow=0,$pvq=0){
    		# byField: 0=ID; 1=Name; 3=special
    		if (!$byField &amp;&amp; is_numeric($v)){ // by ID
    			$r=$fromRow?$fromRow:($v?dbRow(&quot;select * from pages where id=$v limit 1&quot;):array());
    		}
    		else if ($byField == 1){ // by name
    			$name=strtolower(str_replace(&#39;-&#39;,&#39;_&#39;,$v));
    			$fname=&#39;page_by_name_&#39;.md5($name);
    			$r=dbRow(&quot;select * from pages where name like &#39;&quot;.addslashes($name).&quot;&#39; limit 1&quot;);
    		}
    		else if ($byField == 3 &amp;&amp; is_numeric($v)){ // by special
    			$fname=&#39;page_by_special_&#39;.$v;
    			$r=dbRow(&quot;select * from pages where special&amp;$v limit 1&quot;);
    		}
    		else return false;
    		if(!count($r || !is_array($r)))return false;
    		if(!isset($r[&#39;id&#39;]))$r[&#39;id&#39;]=0;
    		if(!isset($r[&#39;type&#39;]))$r[&#39;type&#39;]=0;
    		if(!isset($r[&#39;special&#39;]))$r[&#39;special&#39;]=0;
    		if(!isset($r[&#39;name&#39;]))$r[&#39;name&#39;]=&#39;NO NAME SUPPLIED&#39;;
    		foreach ($r as $k=&gt;$v) $this-&gt;{$k}=$v;
    		$this-&gt;urlname=$r[&#39;name&#39;];
    		$this-&gt;dbVals=$r;
    		self::$instances[$this-&gt;id] =&amp; $this;
    		self::$instancesByName[preg_replace(&#39;/[^a-z0-9]/&#39;,&#39;-&#39;,strtolower($this-&gt;urlname))] =&amp; $this;
    		self::$instancesBySpecial[$this-&gt;special] =&amp; $this;
    		if(!$this-&gt;vars)$this-&gt;vars=&#39;{}&#39;;
    		$this-&gt;vars=json_decode($this-&gt;vars);
    	}
    	function getInstance($id=0,$fromRow=false,$pvq=false){
    		if (!is_numeric($id)) return false;
    		if (!@array_key_exists($id,self::$instances)) self::$instances[$id]=new Page($id,0,$fromRow,$pvq);
    		return self::$instances[$id];
    	}
    	function getInstanceByName($name=&#39;&#39;){
    		$name=strtolower($name);
    		$nameIndex=preg_replace(&#39;#[^a-z0-9/]#&#39;,&#39;-&#39;,$name);
    		if(@array_key_exists($nameIndex,self::$instancesByName))return self::$instancesByName[$nameIndex];
    		self::$instancesByName[$nameIndex]=new Page($name,1);
    		return self::$instancesByName[$nameIndex];
    	}
    	function getInstanceBySpecial($sp=0){
    		if (!is_numeric($sp)) return false;
    		if (!@array_key_exists($sp,$instancesBySpecial)) $instancesBySpecial[$sp]=new Page($sp,3);
    		return $instancesBySpecial[$sp];
    	}



Error message Strict standards: Non-static method should not be called statically in php

I am creating event search application, we set search criteria from one screen populate in another screen then user can edit search criteria from 3rd screen and goes to 4th screen.

To achieve above task i am using static object which remember the values around the application and i don&#39;t need to do any thing extra.

But i am afraid if about static object life cycle in android if low memory found android delete static objects ???

As android supports multi tasking, if user switches to another application and when user comes back application start acting crazy, does static object get removed when it multi task ??? any idea ?? and also suggest holding static object via singleton method is better approach ???

Android static object lifecycle

I&#39;m developing an android application which uses web service to get data from server, for that I&#39;m having three different set of URLs to point development system, test server and live server. It&#39;s difficult to change URL whenever I want to give application for testing/live. so I planned to make it as configurable, so that application can get appropriate URL based on me build type configuration constant. 
So, 

 - which is the best way to keep this constants, java static class or
   java public interface or xml resource file.? **When? Why?**
 - which gives better performance?, **When? Why?**

Ex: xml resource

    &lt;integer name=&quot;config_build_type&quot;&gt;0&lt;/integer&gt;
    &lt;string-array name=&quot;url_authentication&quot;&gt;
        &lt;item &gt;http://development.com/xxxx&lt;/item&gt;
        &lt;item &gt;http://test.com/xxx&lt;/item&gt;
        &lt;item &gt;http://example.com/xxx&lt;/item&gt;
    &lt;/string-array&gt;

Java static constant

    public class Config {
        public static final int BUILD_TYPE = 0; // 0 - development, 1 - test, 2 - live
        public static final String[] URL_AUTHENTICATION = {&quot;http://development.com/&quot;, &quot;http://test.com/&quot;, &quot;http://example.com&quot;};
    }


Which is best way to define constants in android, either static class, interface or xml resource?

Given an hypothetical utility class that is used only in program setup:

    class MyUtils {
       private static MyObject myObject = new MyObject();
       /*package*/static boolean doStuff(Params... params) {
           // do stuff with myObject and params...
       }
    }

will myObject be garbage collected when it is no longer being used, or will it stick around for the life of the program?

Are static fields open for garbage collection?

    class OuterClass {
     class InnerClass {
      static int i = 100; // compile error
      static void f() { } // compile error
     }
    } 

Although it&#39;s not possible to access the static field with `OuterClass.InnerClass.i`, if I want to record something that should be static, e.g. the number of InnerClass objects created, it would be helpful to make that field static. So *why* does Java prohibit static fields/methods in inner classes?

EDIT: I know how to make the compiler happy with static nested class (or static inner class), but what I want to know is why java forbids static fields/methods inside inner classes (or ordinary inner class) from both the language design and implementation aspects, if someone knows more about it.

Why does Java prohibit static fields in inner classes?

What&#39;s the difference between static and non-static enum in Java? Both usages are same.

Is it correct that &lt;del&gt;*all static ones are loaded on memory on startup, and non-static ones are loaded on demand*?&lt;/del&gt;
If yes, then which method is better? Keeping some data always in memory or using server resources to load them each time?

&lt;!-- language: java --&gt;

    public class Test {
	
        public enum Enum1 {
            A, B
        }
	
        public static enum Enum2 {
            C, D
        }
	
        public static void main(String[] args) {
            Enum1 a = Enum1.A;
            Enum1 b = Enum1.B;
		
            Enum2 c = Enum2.C;
            Enum2 d = Enum2.D;
        }
    }

Static enum vs. Non-static enum

I just noticed that `static` members of Swift `structs` are implicitly `lazy`. 

For instance, this will only call the `init` once:

    class Baz {
        init(){
            print(&quot;initializing a Baz&quot;)
        }
    }
    struct Foo {
        static let bar = Baz()
    }
    
    var z = Foo.bar
    z = Foo.bar

What&#39;s the rationale behind this?

What if I want the opposite behaviour?

Implicitly lazy static members in Swift

Say you have a class, 

    class Foo
	{
        public static bar;
    }

When you say:

    new Foo();

I can imagine that in memory, a space is reserved for this object. 

...and when you say again:

    new Foo(); 

...well now you have another space available for the object.

However, where exactly does the static field live?

What I am really trying to learn is:

**How do the references to the objects reference the same field of the objects they reference?** 


How exactly do static fields work internally?

I am a little confused with this matter. I am designing an ORM class that tries to behave very similarly to ActiveRecord in ruby on rails, but that&#39;s beside the point.

What I&#39;m trying to say is that my class makes extensive use of static attribute inheritance, specially for database and table handling. My question is, should I use self:: at all?

PHP Can static:: replace self::?

I&#39;ve seen code like this in a couple of old projects:

    class Class {
        static void Method() {}
    };

    ((Class*)0)-&gt;Method();

This code contains undefined behavior because it includes dereferencing a null pointer (no matter what happens afterwards). It really makes no sense - the cast is there to feed the type name to the compiler and whoever wrote the code above could have written this instead:

    Class::Method();

and the latter would be okay.

Why would anyone write the former code? Is it a known idiom from some good old days or what?

Why would code explicitly call a static method via a null pointer?

What is the best way to have a static member in a non-templated library class,
without placing the burden of defining the member on the class user?

Say I want to provide this class:

    class i_want_a_static_member
    {
        static expensive_resource static_resource_;
    
    public:
        void foo()
        {
            static_resource_.bar();
        }
    };

Then the user of the class must not forget to define the static member somewhere
(as already [answered][1] [many][2] [times][3]):

    // this must be done somewhere in a translation unit
    expensive_resource i_want_a_static_member::static_resource_;

I do have an answer below, but it has some disadvantages. Are there better and/or more elegant solutions?

[1]: https://stackoverflow.com/questions/185844/initializing-private-static-members
[2]: https://stackoverflow.com/questions/3536372/defining-static-members-in-c
[3]: https://stackoverflow.com/questions/1639154/how-to-declare-a-static-const-char-in-your-header-file


How to have static data members in a header-only library?

I am using **private static final LOGGER** field in my class and I want **LOGGER.isInfoEnabled()** method to return **false**.
How can I mock the static final field by using mockito or jMockit

My class is:

      import org.slf4j.Logger;
      import org.slf4j.LoggerFactory;
            
      public class Class1 {
          
      private static final Logger LOGGER = LoggerFactory.getLogger(Class1.class);
          
        public boolean demoMethod() {
           System.out.println(&quot;Demo started&quot;);
           if (LOGGER.isInfoEnabled()) {
             System.out.println(&quot;@@@@@@@@@@@@@@ ------- info is enabled&quot;);
           } else {
             System.out.println(&quot;info is disabled&quot;);
           }
           return LOGGER.isInfoEnabled();
        }
      }

and its junit is :

    import mockit.Mocked;
    import mockit.NonStrictExpectations;
    import org.mockito.InjectMocks;
    import org.mockito.MockitoAnnotations;
    import org.slf4j.Logger;
    import org.testng.annotations.BeforeMethod;
    import org.testng.annotations.Test;
    
    import static org.testng.Assert.*;
    import com.source.Class1;
    
    public class MyTest {
      
      @InjectMocks
      Class1 cls1;
      
      @BeforeMethod
      public void initMocks() {
        MockitoAnnotations.initMocks(this);
      }
      
      @Test
      public void test(@Mocked final Logger LOGGER) {
        
        new NonStrictExpectations() {
          {
            LOGGER.isInfoEnabled();
            result = false;
          }
        };
        assertFalse(cls1.demoMethod());
      }
    }

when I run it the result is:

    -------------------------------------------------------
     T E S T S
    -------------------------------------------------------
    Running com.test.MyTest
    Configuring TestNG with: TestNG652Configurator
    Demo started
    @@@@@@@@@@@@@@ ------- info is enabled
    Tests run: 1, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 1.9 sec &lt;&lt;&lt; FAILURE! - in com.test.MyTest
    test(com.test.MyTest)  Time elapsed: 0.168 sec  &lt;&lt;&lt; FAILURE!
    java.lang.AssertionError: expected [false] but found [true]
            at com.test.MyTest.test(MyTest.java:35)
    
    
    Results :
    
    Failed tests:
      MyTest.test:35 expected [false] but found [true]
    
    Tests run: 1, Failures: 1, Errors: 0, Skipped: 0
    
    [INFO] ------------------------------------------------------------------------
    [INFO] BUILD FAILURE
    [INFO] ------------------------------------------------------------------------
    [INFO] Total time: 9.899s
    [INFO] Finished at: Mon Jun 08 12:35:36 IST 2015
    [INFO] Final Memory: 16M/166M
    [INFO] ------------------------------------------------------------------------
    [ERROR] Failed to execute goal org.apache.maven.plugins:maven-surefire-plugin:2.18.1:test (default-test) on project JMockDemo: The
    re are test failures.
    [ERROR]
    [ERROR] Please refer to D:\perfoce_code\workspace_kepler\JMockDemo\target\surefire-reports for the individual test results.
    [ERROR] -&gt; [Help 1]
    [ERROR]
    [ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
    [ERROR] Re-run Maven using the -X switch to enable full debug logging.
    [ERROR]
    [ERROR] For more information about the errors and possible solutions, please read the following articles:
    [ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException

I am new to jmockit and I want my above junit case to run successfully.
And I have to use JMockit or mockito, can&#39;t use Powermockito.
Please help.

Mock private static final field using mockito or Jmockit

I know you can &lt;del&gt;define them indirectly&lt;/del&gt; *achieve something similar* with companion objects but I am wondering why as a language design were statics dropped out of class definitions.



Why doesn&#39;t Scala have static members inside a class?

Given is a class with a static member.

    class BaseClass
    {
    public:
        static std::string bstring;
    };

String has obviously to be *default-initialized* outside of the class.

    std::string BaseClass::bstring {&quot;.&quot;};

If I include the above line in the header along with the class, I get a `symbol multiply defined` error. It has to be defined in a separate `cpp` file, even with `include guards` or `pragma once`.

Isn&#39;t there a way to define it in the header?



How to initialize static members in the header

I am trying to understand what this means, the code I am looking at has

in `.h`


    typedef void (*MCB)();
    static MCB     m_process;


in `.C`

    MCB Modes::m_process = NULL;


And sometimes when I do

    m_process();

I get segmentations fault, it&#39;s probably because the memory was freed, how can I debug when it gets freed?

What does &quot;typedef void (*Something)()&quot; mean

This code is giving me **incomplete type** error.
What is the problem? Isn&#39;t allowed for a class to have **static member instances** of itself?
Is there a way to achieve the same result?

    struct Size
    {
        const unsigned int width;
        const unsigned int height;
    
        static constexpr Size big = { 480, 240 };
    
        static constexpr Size small = { 210, 170 };
    
    private:
    
        Size( ) = default;
    };

All Static Members Solutions on Gang of Coders

Total of 21 Static Members Solutions