`0xc1` is the `EBCDIC` character set code for `A`. The author is testing for such a machine.

http://www.ibm.com/support/knowledgecenter/en/SSGH4D_15.1.3/com.ibm.xlf1513.aix.doc/language_ref/asciit.html


At first sight might look like that is dead code but &#39;A&#39; == 0x41 not always will return true..

what the developer tried to do here is *lazily* find what encoding is the machine implementing **ASCII** or any variant of **EBCDIC**

as @Richard suggested Capital **a** is mapped to **0xc1** in the [International - Extended Binary Coded Decimal Interchange Code][1]  see table below in the 2 branch of the if else...

[![enter image description here][2]][2]

another different value could be found by ASCII for exmaple:

[![enter image description here][3]][3]

 he could as well have done:

    if(&#39;p&#39; == 0x70) {
      // ...
    } else if(&#39;p&#39; == 0x97) {
      //...
    }



  [1]: https://en.wikipedia.org/wiki/EBCDIC
  [2]: https://i.stack.imgur.com/TmzsN.png
  [3]: https://i.stack.imgur.com/c7IYo.png

Example 1:

    element1.addEventListener(&quot;input&quot;, function() {
    this function does stuff 
    });

Example 2:

    element1 &amp;&amp; element2.addEventListener(&quot;input&quot;, function() {
    this function does stuff
    });

It might not be correct grammatically, but is there a way I can give two elements the same event listener at the same time (same line) instead of having to write them apart?

How to addEventListener to multiple elements in a single line

I have tried to follow [the documentation][1] but was not able to use `urlparse.parse.quote_plus()` in `Python 3`:

    from urllib.parse import urlparse
    
    params = urlparse.parse.quote_plus({&#39;username&#39;: &#39;administrator&#39;, &#39;password&#39;: &#39;xyz&#39;})

I get

&gt;AttributeError: &#39;function&#39; object has no attribute &#39;parse&#39;



  [1]: https://docs.python.org/3.0/library/urllib.parse.html

How to URL encode in Python 3?

I was looking at some C++ code and found the following construct:

    if(&#39;A&#39; == 0x41) {
      // ...
    } else if(&#39;A&#39; == 0xc1) {
      // ...
    } else {
      // ...
    }

I get a [Visual Studio][1] warning saying:

&gt; Warning    C4127 conditional expression is constant.

Visual Studio is clearly right - surely &#39;A&#39; is defined to be 0x41. Why is the author writing this code, given that two out of the three branches are dead code?

  [1]: http://en.wikipedia.org/wiki/Microsoft_Visual_Studio


Why would the character &#39;A&#39; be compared with 0x41?

I was looking at some C++ code and found the following construct:
<pre><code class="hljs language-arduino">if('A' == 0x41) {
 // ...
} else if('A' == 0xc1) {
 // ...
} else {
 // ...
}
</code></pre>
I get a <a href="http://en.wikipedia.org/wiki/Microsoft_Visual_Studio" target="_blank" rel="noopener noreferrer">Visual Studio</a> warning saying:
> Warning C4127 conditional expression is constant.
Visual Studio is clearly right - surely 'A' is defined to be 0x41. Why is the author writing this code, given that two out of the three branches are dead code?

Prelude:

    std::tuple&lt;int, int, int&gt; f();
    std::tuple&lt;int, int, float, int&gt; g();

C++1z will introduce syntax for structured bindings which will make it possible to write instead of

    int a, b, c;
    std::tie(a, b, c) = f();

something like

    auto [a, b, c] = f();

However, `std::tie` also allowed to specify `std::ignore` to ignore certain components, e.g:

    std::tie(a, b, std::ignore, c) = g();

Will it be possible to do something similar using the new structured bindings syntax? How would it work?

std::ignore with structured bindings?

Consider the following class:

    struct S { ~S() = delete; };

Shortly and for the purpose of the question: I cannot create instances of `S` like `S s{};` for I could not destroy them.  
As mentioned in the comments, I can still create an instance by doing `S *s = new S;`, but I cannot delete it as well.  
Therefore, the only use I can see for a deleted destructor is something like this:

    struct S {
        ~S() = delete;
        static void f() { }
    };

    int main() {
        S::f();
    }

That is, define a class that exposes only a bunch of static functions and forbid any attempt to create an instance of that class.

What are the other uses (if any) of a deleted destructor?

Uses of destructor = delete;

I was browsing some C++ code, and found something like this:

    (a + (b &amp; 255)) &amp; 255

The double AND annoyed me, so I thought of:

    (a + b) &amp; 255

(`a` and `b` are 32-bit unsigned integers)

I quickly wrote a test script (JS) to confirm my theory:

&lt;!-- begin snippet: js hide: false console: true babel: false --&gt;

&lt;!-- language: lang-js --&gt;

    for (var i = 0; i &lt; 100; i++) {
        var a = Math.ceil(Math.random() * 0xFFFF),
            b = Math.ceil(Math.random() * 0xFFFF);

        var expr1 = (a + (b &amp; 255)) &amp; 255,
            expr2 = (a + b) &amp; 255;

        if (expr1 != expr2) {
            console.log(&quot;Numbers &quot; + a + &quot; and &quot; + b + &quot; mismatch!&quot;);
            break;
        }
    }

&lt;!-- end snippet --&gt;

While the script confirmed my hypothesis (both operations are equal), I still don&#39;t trust it, because 1) [random](https://xkcd.com/221/) and 2) I&#39;m not a mathematician, [I have no idea what am I doing](http://i.imgur.com/Boq967h.png).

Also, sorry for the Lisp-y title. Feel free to edit it.

Is ((a + (b &amp; 255)) &amp; 255) the same as ((a + b) &amp; 255)?

According to Scott Meyers, one area where C++ shines over C is that function objects are faster than function pointers. He says this is because function objects are inlined, which increases speed.

I have two questions about this:

 1. How can we verify that function objects are, in fact, inlined? Can we verify this in practice?

 2. Does the inlining of function objects depend on the compiler we use, or do all compilers behave like this?


Are functors actually faster than pointers to functions?

[cppreference](http://en.cppreference.com/mwiki/index.php?title=cpp/language/default_constructor&amp;oldid=86081#Trivial_default_constructor)&lt;sup&gt;&amp;dagger;&lt;/sup&gt; states that:

&gt; Objects with trivial default constructors can be created by using `reinterpret_cast` on any suitably aligned storage, e.g. on memory allocated with `std::malloc`.

This implies that the following is well-defined code:

    struct X { int x; };
    alignas(X) char buffer[sizeof(X)];    // (A)
    reinterpret_cast&lt;X*&gt;(buffer)-&gt;x = 42; // (B)

Three questions follow:

1. Is that quote correct? 
2. If yes, at what point does the lifetime of the `X` begin? If on line `(B)`, is it the cast itself that is considered acquiring storage? If on line `(A)`, what if there were a branch between `(A)` and `(B)` that would conditionally construct an `X` or some other pod, `Y`?
3. Does anything change between C++11 and C++1z in this regard?

&lt;hr /&gt;

&lt;sup&gt;&amp;dagger;&lt;/sup&gt;Note that this is an old link. The wording was changed in response to this question. It now reads:

&gt; Unlike in C, however, objects with trivial default constructors cannot be created by simply reinterpreting suitably aligned storage, such as memory allocated with `std::malloc`: placement-new is required to formally introduce a new object and avoid potential undefined behavior.

reinterpret_cast creating a trivially default-constructible object

I have some error like this &quot;Expression implicitly coerced from `String?` to `Any`&quot; this is my code :

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -&gt; Bool {
        // Override point for customization after application launch.
        
        FIRApp.configure()
        FIRAuth.auth()?.signIn(withEmail: &quot;myemail@gmail.com&quot;, password: &quot;mypassword&quot;, completion: { (user, error) in
            if (error != nil) {
                print(user?.email)
            }else {
                print(error?.localizedDescription)
            }
        })
        
        return true
    }

Error in this line 

    print(user?.email)

And

    print(error?.localizedDescription)

Please help me

Expression implicitly coerced from &#39;String?&#39; to Any

I am working on a project using Typescript and some of the ES6 features exposed by Typescript like ES6 String Literals e.g. `` `Something ${variable} Something else` ``.

Whilst debugging a problem I dropped a breakpoint into my typescript file to step through it in the source panel, which usually works fine.

But Chrome Dev Tools has an issue with ES6 String literals and doesn&#39;t seem to recognise the end of an ES6 String literal.

Instead all code following the string literal is marked red (string highlighting in debugger) and blocked from variable inspection as chrome debugger seems to think it is all one massive string.

Has someone encountered this issue, found a fix or knows whether this is on Google&#39;s roadmap for Chrome Dev Tools?

**EDIT 1:**  
Looks like this issue is currently being worked on by the Chromium team. See issue report for updates:  
[bugs.chromium.org/p/chromium/issues/detail?id=659515][1]

**EDIT 2:**
Bug has been open for quite some time, but doesn&#39;t seem to have been prioritised. If you experience the issue go to the chromium link above and star/comment on it with helpful info to move it into focus of the Dev Tools team.   


  [1]: http://bugs.chromium.org/p/chromium/issues/detail?id=659515

Chrome Dev Tools Issue With ES6 String Literals/Typescript

I have a python Code that will recognize speech using the Google STT engine and give me back the results but I get the results in strings with &quot;quotes&quot;. I don&#39;t want that quotes in my code as I will use it to run many commands and it doesn&#39;t work. I haven&#39;t tried anything so far as I didn&#39;t get anything to try!
This is the function in the  python code that will recognize speech:

    def recog():
        p = subprocess.Popen([&#39;./speech-recog.sh&#39;], stdout=subprocess.PIPE,
                                                stderr=subprocess.PIPE)
        global out,err
        out, err = p.communicate()
        print out

This is speech-recog.sh:
    
    #!/bin/bash

    hardware=&quot;plughw:1,0&quot;
    duration=&quot;3&quot;
    lang=&quot;en&quot;
    hw_bool=0
    dur_bool=0
    lang_bool=0
    for var in &quot;$@&quot;
    do
        if [ &quot;$var&quot; == &quot;-D&quot; ] ; then
            hw_bool=1
        elif [ &quot;$var&quot; == &quot;-d&quot; ] ; then
            dur_bool=1
        elif [ &quot;$var&quot; == &quot;-l&quot; ] ; then
            lang_bool=1
        elif [ $hw_bool == 1 ] ; then
            hw_bool=0
            hardware=&quot;$var&quot;
        elif [ $dur_bool == 1 ] ; then
            dur_bool=0
            duration=&quot;$var&quot;
        elif [ $lang_bool == 1 ] ; then
            lang_bool=0
            lang=&quot;$var&quot;
        else
            echo &quot;Invalid option, valid options are -D for hardware and -d for duration&quot;
        fi
    done

    arecord -D $hardware -f S16_LE -t wav -d $duration -r 16000 | flac - -f --best --sample-rate 16000 -o /dev/shm/out.flac 1&gt;/dev/shm/voice.log 2&gt;/dev/shm/voice.log; curl -X POST --data-binary @/dev/shm/out.flac --user-agent &#39;Mozilla/5.0&#39; --header &#39;Content-Type: audio/x-flac; rate=16000;&#39; &quot;https://www.google.com/speech-api/v2/recognize?output=json&amp;lang=$lang&amp;key=key&amp;client=Mozilla/5.0&quot; | sed -e &#39;s/[{}]/&#39;&#39;/g&#39; | awk -F&quot;:&quot; &#39;{print $4}&#39; | awk -F&quot;,&quot; &#39;{print $1}&#39; | tr -d &#39;\n&#39;

    rm /dev/shm/out.flac
This was taken from Steven Hickson&#39;s Voicecommand Program made for Raspberry Pi

Remove quotes from String in Python

A new Rustacean like me struggles with juggling these types: `String`, `&amp;str`, `Vec&lt;u8&gt;`, `&amp;[u8]`.

In time, I hope to have an epiphany and suddenly get why some library calls use one or the other. Until then, I need help to map out each idiomatic transition.

Given these types:

    let st: &amp;str = ...;
    let s:  String = ...;
    let u:  &amp;[u8] = ...;
    let v:  Vec&lt;u8&gt; = ...;

I think I have figured these out, but are they idiomatic?

&lt;!-- language: none --&gt;

    &amp;str    -&gt; String    String::from(st)
    &amp;str    -&gt; &amp;[u8]     st.as_bytes()
    String  -&gt; &amp;str      s.as_str()
    &amp;[u8]   -&gt; &amp;str      str::from_utf8(u)
    Vec&lt;u8&gt; -&gt; String    String::from_utf8(v)

Ultimately I want a complete table of transitions for these types:

&lt;!-- language: none --&gt;

    &amp;str    -&gt; String
    &amp;str    -&gt; &amp;[u8]
    &amp;str    -&gt; Vec&lt;u8&gt;
    String  -&gt; &amp;str
    String  -&gt; &amp;[u8]
    String  -&gt; Vec&lt;u8&gt;
    &amp;[u8]   -&gt; &amp;str
    &amp;[u8]   -&gt; String
    &amp;[u8]   -&gt; Vec&lt;u8&gt;
    Vec&lt;u8&gt; -&gt; &amp;str
    Vec&lt;u8&gt; -&gt; String
    Vec&lt;u8&gt; -&gt; &amp;[u8]


How do I convert between String, &amp;str, Vec&lt;u8&gt; and &amp;[u8]?

I came across *[“CorruptedString” (Solution)][1]*. Here is following code of program from the book:

    var s = &quot;Hello&quot;;
    string.Intern(s);
    unsafe
    {
      fixed (char* c = s)
        for (int i = 0; i &lt; s.Length; i++)
          c[i] = &#39;a&#39;;
    }
    Console.WriteLine(&quot;Hello&quot;); // Displays: &quot;aaaaa&quot;

Why does this program display &quot;aaaaa&quot;? I understand this program as follows:

 1. The [CLR][2] reserves &quot;hello&quot; in the intern pool (I image the intern pool as a set of strings).
 2. `string.Intern(s)` actually does nothing, because the CLR had reserved &quot;Hello&quot; string - it just returns address of reserved &quot;Hello&quot; string (object s has the same address)
 3. The program changes the content of the &quot;Hello&quot; string via a pointer
 4. ??? The Hello string should be absent in the intern pool, and it should be error! But it is OK; the program runs successfully.

As I understand the intern pool, it is like some kind of dictionary of string to string. Or maybe I missed something?

  [1]: http://problembook.net/content/en/Strings/CorruptedString-S.html
  [2]: http://en.wikipedia.org/wiki/Common_Language_Runtime



Content Type	Original Author	Original Content on Stackoverflow
Question	H Bellamy	View Question on Stackoverflow
Solution 1 - C++	Richard Hodges	View Answer on Stackoverflow
Solution 2 - C++	ΦXocę 웃 Пepeúpa ツ	View Answer on Stackoverflow

Why would the character 'A' be compared with 0x41?

C++ Problem Overview

C++ Solutions

Solution 1 - C++

Solution 2 - C++

How to URL encode in Python 3?

How to addEventListener to multiple elements in a single line

Attributions