No, there&#39;s no difference - you just tell that class B is a friend of class A and now can access its private and protected members, that&#39;s all.

Since the syntax `friend class B` doesn&#39;t declare  a *member* of the class `A`, so it doesn&#39;t matter where you write it, class `B` is a friend of class `A`. 

Also, if you write `friend class B` in `protected` section of `A`, then it does NOT mean that `B` can access only `protected` and `public` members of `A`.  

Always remember that once `B` becomes a friend of `A`, it can access *any* member of `A`, no matter in which section you write `friend class B`.

c++ has the notion of &#39;hidden friends&#39;: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1601r0.pdf

Which only applies to friend functions that are defined inline. This make it so the functions can only be found via argument-dependent lookups, removing them from enclosing namespace.

The friend declaration appears in a class body and grants a function or another class access to private and protected members of the class where the friend declaration appears. 

As such access specifiers have no effect on the meaning of friend declarations (they can appear in private: or in public: sections, with no difference).

For reading files in Scala, there is 

    Source.fromFile(&quot;file.txt&quot;).mkString

Is there an equivalent and concise way to write a string to file?

Most languages support something like that. My favorite is Groovy:

    def f = new File(&quot;file.txt&quot;)
    // Read
    def s = f.text
    // Write
    f.text = &quot;file contents&quot;

I&#39;d like to use the code for programs ranging from a single line to a short page of code. Having to use your own library doesn&#39;t make sense here. I expect a modern language to let me write something to a file conveniently. 

There are posts similar to this, but they don&#39;t answer my exact question or are focused on older Scala versions.

For example:

* https://stackoverflow.com/questions/1284423/read-entire-file-in-scala
* https://stackoverflow.com/questions/4604237/how-to-write-to-a-file-in-scala


Scala: write string to file in one statement

I want to create a map object in javascript. I came to the following idea:

     var a = new Array();
     a[&quot;key1&quot;] = &quot;value1&quot;;
     a[&quot;key2&quot;] = &quot;value2&quot;;

but then how I can find if a particular key exists or not?


How to create a hash or dictionary object in JavaScript

Is there a difference between declaring a friend function/class as private or public? I can&#39;t seem to find anything about this online.

I mean the difference between:

    class A
    {
     public: 
          friend class B;
     };


and

    class A
    {
     private: //or nothing as the default is private
          friend class B;
     };

Is there a difference?

Friend declaration in C++ - difference between public and private

Is there a difference between declaring a friend function/class as private or public? I can't seem to find anything about this online.
I mean the difference between:
<pre><code class="hljs language-arduino">class A
{
 public: 
 friend class B;
 };
</code></pre>
and
<pre><code class="hljs language-vbnet">class A
{
 private: //or nothing as the default is private
 friend class B;
 };
</code></pre>
Is there a difference?

2 valid versions of `main()` exist in `C++`:

    int main()  // version 1
    int main(int argc, char **argv)  // version 2

But both overloads cannot coexist at the same time. Why not? (Potential use case: while running the program from the terminal, if no arguments are passed the first version is called, otherwise the second version is.)

Does the compiler perform a special check to allow just one version per binary? 


Is main() overloaded in C++?

Can someone explain it in a language that mere mortals understand?

What does the [[carries_dependency]] attribute mean?

I like to give helpful errors / messages, and I also want to do so for my `static_assert`s. The problem is, that they depend on template parameters. Normally, those parameters will get displayed on way or an other due to the error raised, but they are either obscure or not grouped so they make sense. Example:

    template&lt;class T&gt;
    struct fake_dependency{
      static bool const value = false;
    };
    
    template&lt;class T, class Tag&gt;
    struct Foo{
      Foo(){}

      template&lt;class OtherTag&gt;
      Foo(Foo&lt;T, OtherTag&gt; const&amp;){
        static_assert(fake_dependency&lt;T&gt;::value, &quot;Cannot create Foo&lt;T,Tag&gt; from Foo&lt;T,OtherTag&gt;.&quot;);
      }
    };

    int main(){
        Foo&lt;int, struct TagA&gt; fA;
        Foo&lt;int, struct TagB&gt; fB(fA);
    }

Output on MSVC:

    src\main.cpp(74): error C2338: Cannot create Foo&lt;T,Tag&gt; from Foo&lt;T,OtherTag&gt;.
              src\main.cpp(84) : see reference to function template instantiation &#39;Foo&lt;T,Tag&gt;::Foo&lt;main::TagA&gt;(const Foo&lt;T,main::TagA&gt; &amp;)&#39; being compiled
              with
              [
                  T=int,
                  Tag=main::TagB
              ]
One tag is mentioned in the function template itself, the other below with the class template. Not so nice. Lets see what [GCC outputs][1]:

    prog.cpp: In constructor &#39;Foo&lt;T, Tag&gt;::Foo(const Foo&lt;T, OtherTag&gt;&amp;) [with OtherTag = main()::TagA, T = int, Tag = main()::TagB]&#39;:
    prog.cpp:18:32:   instantiated from here
    prog.cpp:12:5: error: static assertion failed: &quot;Cannot create Foo&lt;T,Tag&gt; from Foo&lt;T,OtherTag&gt;.&quot;

Much better, but still not really where the `static_assert` is. And now imagine some more parameters, or more templates, or both. *shivers*

One way to work around that is to use an intermediate struct, which takes both Tags as template parameters:

    template&lt;class Tag, class OtherTag&gt;
    struct static_Foo_assert{
        static_assert(fake_dependency&lt;Tag&gt;::value, &quot;Cannot create Foo&lt;T,Tag&gt; from Foo&lt;T,OtherTag&gt;.&quot;);
    };

    template&lt;class T, class Tag&gt;
    struct Foo{
      Foo(){}
    
      template&lt;class OtherTag&gt;
      Foo(Foo&lt;T, OtherTag&gt; const&amp;){
          static_Foo_assert&lt;Tag, OtherTag&gt; x;
      }
    };
Now lets see the output again:

    src\main.cpp(70): error C2338: Cannot create Foo&lt;T,Tag&gt; from Foo&lt;T,OtherTag&gt;.
              src\main.cpp(79) : see reference to class template instantiation &#39;static_Foo_assert&lt;Tag,OtherTag&gt;&#39; being compiled
              with
              [
                  Tag=main::TagB,
                  OtherTag=main::TagA
              ]
Much better! Here&#39;s what [GCC says][2]:

    prog.cpp: In instantiation of &#39;static_Foo_assert&lt;main()::TagB, main()::TagA&gt;&#39;:
    prog.cpp:17:40:   instantiated from &#39;Foo&lt;T, Tag&gt;::Foo(const Foo&lt;T, OtherTag&gt;&amp;) [with OtherTag = main()::TagA, T = int, Tag = main()::TagB]&#39;
    prog.cpp:23:32:   instantiated from here
    prog.cpp:8:5: error: static assertion failed: &quot;Cannot create Foo&lt;T,Tag&gt; from Foo&lt;T,OtherTag&gt;.&quot;

Looks not bad. The problem: I need to create such a struct for every template, since the error message in `static_assert` needs to be a string literal...

Now, for my question: Can we somehow include the type names directly into the `static_assert`? Like

    static_assert(..., &quot;Cannot create Foo&lt;&quot; T &quot;,&quot; Tag &quot;&gt; from Foo&lt;&quot; T &quot;,&quot; OtherTag &quot;&gt;.&quot;);
Example output:
&gt;Cannot create `Foo&lt;int,main::TagA&gt;` from `Foo&lt;int,main::TagB&gt;`.

Or, if that isn&#39;t achievable, can we somehow make the error message an extra template parameter, as to make it passable?


  [1]: http://ideone.com/ElIm1
  [2]: http://ideone.com/pHLAq

Integrate type name in static_assert output?

I am trying to grab the raw filename without the extension from the filename passed in arguments:

    int main ( int argc, char *argv[] )
    {
        // Check to make sure there is a single argument
    	if ( argc != 2 )
    	{
    		cout&lt;&lt;&quot;usage: &quot;&lt;&lt; argv[0] &lt;&lt;&quot; &lt;filename&gt;\n&quot;;
    		return 1;
    	}
    	
    	// Remove the extension if it was supplied from argv[1] -- pseudocode
        char* filename = removeExtension(argv[1]);
        
        cout &lt;&lt; filename;
        
    }


The filename should for example be &quot;test&quot; when I passed in &quot;test.dat&quot;.

Easy way to remove extension from a filename?

Is it possible to get a C++ application running in Windows to request administrator privileges from the operating system at run time?

I know it can be done at compile time, but can&#39;t seem to find anywhere whether it can be done at run time.

Thanks for your help!

EDIT: What if I want the current instance to have elevated privileges? For example, I might have data stored in memory which I want to keep.

Requesting administrator privileges at run time

I have a question about private constructors in C++. If the constructor is private, how can I create an instance of the class?

Should we have a getInstance() method inside the class?




When do we need a private constructor in C++?

I have been assigned the task of unit testing a class that I never worked directly on with JUnit, and am strictly forbidden to change the code in the package.  This is usually no issue, since most of our unit testing is just for functionality and input/output consistency, which can be done simply by running routines and checking their return values.

However, occasionally there is a need to check a private variable within the class, or directly edit a private variable to check some internal behavior.  Is there a way to gain access to these, whether through JUnit or any other way, for the purpose of unit testing without actually changing any of the code in the original source package?  And if not, how do programmers handle this issue in the real world where a unit tester may not be the same person as the coder?

JUnit Testing private variables?

I have a class that benefits from the use of constants in its internal implementation, but I would like to limit visibility of these constants. Why doesn&#39;t PHP permit private constants?  Is there another way to achieve this or is PHP trying to discourage some type of design misstep I am ignorant of?

Why doesn&#39;t PHP permit private const?

If a variable is declared as `public static varName;`, then I can access it from anywhere as `ClassName.varName`. I am also aware that static members are shared by all instances of a class and are not reallocated in each instance.

Is declaring a variable as `private static varName;` any different from declaring a variable `private varName;`?

In both cases it cannot be accessed as `ClassName.varName` or as `ClassInstance.varName` from any other class.

Does declaring the variable as static give it other special properties?

What is the use of a private static variable in Java?

How do I create a private constructor which should be called only by the static function of the class and not from else where?


Private Constructor in Python

I am trying to relearn C++ after taking an intro course a few years ago and I’m having some basic problems. My current problem occurs when trying to use a friend function. Here is my code in 2 files.

First:

    // fun.cpp
    
    #include &lt;iostream&gt;
    using namespace std;

    class classA {
    	friend void funct();
    public:
    	classA(int a=1,int b=2):propa(a),propb(b){cout&lt;&lt;&quot;constructor\n&quot;;}
    private:
    	int propa;
    	int propb;
    	void outfun(){
    		cout&lt;&lt;&quot;propa=&quot;&lt;&lt;propa&lt;&lt;endl&lt;&lt;&quot;propb=&quot;&lt;&lt;propb&lt;&lt;endl;
    	}
    };
    void funct(){                     // ERROR HERE
    	cout&lt;&lt;&quot;enter funct&quot;&lt;&lt;endl;
    	classA tmp(1,2);
    	tmp.outfun();
    	cout&lt;&lt;&quot;exit funct&quot;&lt;&lt;endl;
    }

Second:

    // mainfile.cpp
    #include &lt;iostream&gt;
    #include &quot;fun.cpp&quot;
    using namespace std;
    
    int main(int nargin,char* varargin[]) {
    	cout&lt;&lt;&quot;call funct&quot;&lt;&lt;endl;
    	funct();
    	cout&lt;&lt;&quot;exit main&quot;&lt;&lt;endl;
    	return 0;
    }

The error I am getting is &quot;multiple definition of `funct()&#39;&quot;. Am I using the wrong syntax when declaring it as a friend function?

Error with multiple definitions of function

I&#39;m currently on a public WIFI spot and I&#39;m unable to use SSH (they probably blocked that port). However, I need that connection to do a `git push`.

    ➜ ssh -T git@github.com
    ssh: connect to host github.com port 22: Connection refused

Is it possible to bypass this restriction by setting up a SSH tunnel via port 80 and tell `github push` to use that connection? How to do that? I&#39;m on OSX (lion). This must be a common problem?


Github (SSH) via public WIFI, port 22 blocked

There is a lot of code in one of our projects that looks like this:

    internal static class Extensions
    {
        public static string AddFoo(this string s)
        {
            if (s == null)
            {
                return &quot;Foo&quot;;
            }

            return $({s}Foo);
        }
    }

Is there any explicit reason to do this other than &quot;it is easier to make the type public later?&quot;

I suspect it only matters in very strange edge cases (reflection in Silverlight) or not at all.

Why use a public method in an internal class?

In Java, it&#39;s taught that variables should be kept private to enable better encapsulation, but what about static constants? This:

    public static final int FOO = 5;

Would be equivalent in result to this:

    private static final int FOO = 5;
    ...
    public static getFoo() { return FOO; }
But which is better practice?

&#39;public static final&#39; or &#39;private static final&#39; with getter?

&gt; **Possible Duplicate:**  
&gt; [Why use getters and setters?](https://stackoverflow.com/questions/1568091/why-use-getters-and-setters)  

&lt;!-- End of automatically inserted text --&gt;

Is there any advantage to making methods to access private variables in your class instead of making the variable public?

For example is the second case better than the first?

    //Case 1
    public class Shoe{
        public int size;
    }
    
    //Case 2
    public class Shoe{
        private int size;
        public int getSize(){
            return size;
        }
    
        public void setSize(int sz){
            size = sz;
        }
    
    }

Advantage of set and get methods vs public variable

&gt; **Possible Duplicate:**  
&gt; [Call-time pass-by-reference has been deprecated](https://stackoverflow.com/questions/4665782/call-time-pass-by-reference-has-been-deprecated)  

&lt;!-- End of automatically inserted text --&gt;

While it may be documented somewhere on the internet, I cannot find a solution to my problem. Since the PHP 5.4 update, pass-by-references have been removed. 

Now I have a problem with this section of code, and I hope somebody can see what I&#39;m trying to do with it so that they can possibly help me with a solution to overcome my pass-by-reference problem.

Below is the code in question: 

    public function trigger_hooks( $command, &amp;$client, $input ) {
        if( isset( $this-&gt;hooks[$command] ) ) {
            foreach( $this-&gt;hooks[$command] as $func ) {
                PS3socket::debug( &#39;Triggering Hook \&#39;&#39; . $func . &#39;\&#39; for \&#39;&#39; . $command . &#39;\&#39;&#39; );
                $continue = call_user_func( $func, &amp;$this, &amp;$client, $input );
                if( $continue === FALSE ) {
                    break;
                }
            }
        }
    }
.



Content Type	Original Author	Original Content on Stackoverflow
Question	BIU	View Question on Stackoverflow
Solution 1 - C++	sharptooth	View Answer on Stackoverflow
Solution 2 - C++	Nawaz	View Answer on Stackoverflow
Solution 3 - C++	Alfred Fuller	View Answer on Stackoverflow
Solution 4 - C++	goyuiitv	View Answer on Stackoverflow

Friend declaration in C++ - difference between public and private

C++ Problem Overview

C++ Solutions

Solution 1 - C++

Solution 2 - C++

Solution 3 - C++

Solution 4 - C++

How to create a hash or dictionary object in JavaScript

Scala: write string to file in one statement

Attributions