I get a warning:

&gt; Imaginary constants are a GNU extension

The `J` suffix is a GNU extension, which causes the literal to be of a `_Complex` type.

More info here: https://gcc.gnu.org/onlinedocs/gcc/Complex.html

As zenith mentioned, this is a GNU extension for writing imaginary literals. I really want to comment on the rationale of using `j` for this purpose as imallett is wondering but I don&#39;t have enough reputation to comment on zenith&#39;s answer. I&#39;ll leave this as an answer anyway as it might be helpful to others.

As [this link][1] explains, both `i` and `j` can be used to write imaginary literals using this GNU extension. The reason why `i` is used for this is obvious, but the reason why `j` is used as well is that `j` is commonly used to denote the imaginary unit in electrical engineering and control systems engineering to prevent confusion as `i` is already used to denote electrical current in those contexts.

  [1]: https://gcc.gnu.org/onlinedocs/gcc/Complex.html

Could anybody tell me more about difference between physical replication and logical replication in PostgreSQL?

Difference between Stream Replication and logical replication

I have added a new property to my existing model. It&#39;s a bool property with a default value of true. There are existing data in this table and I would like to set one specific row&#39;s new property to false right after creating the new field, in the Up method. 

    public override void Up()
    {
        AddColumn(&quot;dbo.RequestValidationErrors&quot;, &quot;IsBreaking&quot;,
             c =&gt; c.Boolean(nullable: false));
        using (Context ctx = new Context())
        {
            var validation = 
                ctx.RequestValidationErrorSet
                .FirstOrDefault
                    (x =&gt; x.WordCode == &quot;RequestValidationError.MoreThanOneItemFound&quot;);
                if (validation != null)
                {
                    validation.IsBreaking = false;
                    ctx.SaveChanges();
                }
            }
        }
    }
This way EF throws an error during saying 

&gt; System.InvalidOperationException: The model backing the
&gt; &#39;DbContext&#39; context has changed since the database was created.
&gt; Consider using Code First Migrations to update the database

Is it possible to change the database here or should I do it elsewhere?


Change data in migration Up method - Entity Framework

I have the following source:

    int main() { 000J; }

With gcc 4.8.4 it compiles without errors.
I know there are suffixes like L or U, but I didn&#39;t find anything about J.

So what does it do?


What does the integer suffix J mean?

I have the following source:
<pre><code class="hljs language-csharp">int main() { 000J; }
</code></pre>
With gcc 4.8.4 it compiles without errors.
I know there are suffixes like L or U, but I didn't find anything about J.
So what does it do?

We can write an `if` statement as

    if (a == 5, b == 6, ... , thisMustBeTrue)

and only the last condition should be satisfiable to enter the `if` body.

why is it allowed?


What is the advantage of commas in a conditional statement?

Consider this strange program:

    int main()
    {
        int(*){} Is it C++14 or any other language?
    }

(See a live demo [here][1] &amp; [here][2].)

**Even though the comment `//` is missing,** the code compiles fine without any errors &amp; warnings even when I use `-pedantic-errors`options in g++ 6.0. This seems like a compiler bug to me. Is it really a bug in the compiler?


  [1]: http://melpon.org/wandbox/permlink/YYiMrSh2AIrHxbWy
  [2]: http://cpp.sh/46vs

Why does this invalid-looking code compile successfully on g++ 6.0?

I&#39;m really eager to start using Google&#39;s new Tensorflow library in C++. The website and docs are just really unclear in terms of how to build the project&#39;s C++ API and I don&#39;t know where to start. 

Can someone with more experience help by discovering and sharing a guide to using tensorflow&#39;s C++ API?  

How to build and use Google TensorFlow C++ api

I&#39;m looking for a `clang-format` setting to prevent the tool from removing line breaks.

For example, I have my `ColumnLimit` set to 120, and here&#39;s what happens when I reformat some sample code.

Before:

    #include &lt;vector&gt;
    #include &lt;string&gt;
    
    std::vector&lt;std::string&gt; get_vec()
    {
       return std::vector&lt;std::string&gt; {
          &quot;this is a test&quot;,
          &quot;some of the lines are longer&quot;,
          &quot;than other, but I would like&quot;,
          &quot;to keep them on separate lines&quot;
       };
    }
    
    int main()
    {
       auto vec = get_vec();
    }

After:

    #include &lt;vector&gt;
    #include &lt;string&gt;
    
    std::vector&lt;std::string&gt; get_vec()
    {
       return std::vector&lt;std::string&gt;{&quot;this is a test&quot;, &quot;some of the lines are longer&quot;, &quot;than other, but I would like&quot;,
             &quot;to keep them on separate lines&quot;};
    }
    
    int main()
    {
       auto vec = get_vec();
    }


What I would like is that the tool breaks lines that are over 120 characters, but doesn&#39;t decide to combine lines just because they are less than 120 characters.

Is there such an option?  Nothing in the docs stood out to me.



Clang-format line breaks

I used `Sleep(500)` in my code and I used `getTickCount()` to test the timing. I found that it has a cost of about 515ms, more than 500. Does somebody know why that is?


Why does Sleep(500) cost more than 500ms?

In my University&#39;s C programming class, the professor and subsequent book written by her uses the term **call or pass by reference** when referring to **pointers** in C.

An example of what is considered a &#39;call by reference function&#39; by my professor:

    int sum(int *a, int *b);

An example of what is considered a &#39;call by value function&#39; by my professor:

    int sum(int a, int b);

I&#39;ve [read][1] C doesn&#39;t support call by reference. To my understanding, **pointers pass by value**.

Basically, is it **incorrect** to say pointers are C&#39;s way of passing by reference? Would it be **more correct** to say you cannot pass by reference in C but can use pointers as an alternative?

---

**Update 11/11/15**

From the way my question originated, I believe a debate of terminology has stemmed and in fact I&#39;m seeing two specific distinctions.

 - pass-by-reference (the term used mainly today): The **specific** term as used in languages like C++
 - pass-by-reference (the term used by my professor as a paradigm to explain pointers): The **general** term used before languages like C++ were developed and thus before the term was rewritten

After reading @Haris&#39; updated answer it makes sense why this isn&#39;t so black and white.

  [1]: https://stackoverflow.com/questions/1919718/pass-by-reference-in-c
  [2]: https://stackoverflow.com/questions/57483/what-are-the-differences-between-a-pointer-variable-and-a-reference-variable-in?rq=1

Are pointers considered a method of calling by reference in C?

Program:

    #include&lt;stdio.h&gt;

    int main(void) {
        int x[4];
        printf(&quot;%p\n&quot;, x);
        printf(&quot;%p\n&quot;, x + 1);
        printf(&quot;%p\n&quot;, &amp;x);
        printf(&quot;%p\n&quot;, &amp;x + 1);
    }

Output:

    $ ./a.out
    0xbff93510
    0xbff93514
    0xbff93510
    0xbff93520
    $

I expect that the following is the output of the above program. For example:

    x        // 0x100
    x+1      // 0x104  Because x is an integer array
    &amp;x       // 0x100  Address of array
    &amp;x+1     // 0x104

But the output of the last statement is different from whast I expected. `&amp;x` is also the address of the array. So incrementing 1 on this
will print the address incremented by 4. But `&amp;x+1` gives the address incremented by 10.  Why?


Different Pointer Arithmetic Results when Taking Address of Array

I&#39;ve been asked in a recent interview about C++ struct fields alignment and theoretized that C and C++ follows the same strategy in struct packing. 

Hovewer, it was the wrong assumption. The interviewer said that in general C and C++ are packing structs in different ways and we should never expect the opposite. IMHO it&#39;s strange statement. There is no `pack &quot;C&quot;` qualifier for structs in C++ for using in bilingual C/C++ header files.

So in practice it could mean that you can&#39;t create a struct in C++ and pass it to a C library because in general its fields will be aligned in a different way and have different offsets. But, in fact, most programmers seriously rely on this interoperability up to the point when they convert a pointer to a C [POD][1] struct to a reference to C++ wrapper around this struct with some helper methods. Can you please clarify this matter?

  [1]: http://en.wikipedia.org/wiki/Plain_old_data_structure


C vs C++ struct alignment

I&#39;m working on an old code base and pretty much every invocation of free() uses a cast on its argument. For example,

	free((float *)velocity);
	free((float *)acceleration);
	free((char *)label);

where each pointer is of the corresponding (and matching) type. I see no point in doing this at all. It&#39;s very old code, so I&#39;m left wondering if it&#39;s a K&amp;R thing. If so, I actually wish to support the old compilers that may have required this, so I don&#39;t want to remove them.

Is there a technical reason to use these casts? I don&#39;t even see much of a pragmatic reason to use them. What&#39;s the point of reminding ourselves of the data type right before freeing it?

EDIT: This question is *not* a duplicate of the other question. The other question is a special case of this question, which I think is obvious if the close voters would have read all the answers.

Colophon: I&#39;m giving the checkmark to the answer that gave a reason why this might still need to be done; however, the answer about it being a pre-ANSI C custom (at least among some programmers) seems to be the reason it was used in my case. If there were two checkmarks to give they&#39;d both get one. Lots of good points by many people here. Thank you for your contributions.

In C, why do some people cast the pointer before freeing it?

I have seen the following macro definitions in a coding book.

    #define TRUE  &#39;/&#39;/&#39;/&#39;
    #define FALSE &#39;-&#39;-&#39;-&#39;

There was no explanation there.

Please explain to me how these will work as `TRUE` and `FALSE`.

Strange definitions of TRUE and FALSE macros

I am just starting to learn Javascript and I immediately got confused by seemingly contradictory statements in Mozilla&#39;s [A re-introduction to JavaScript (JS tutorial)][1].

One one hand:

&gt; &quot;**There&#39;s no such thing as an integer** in JavaScript, so you have to
&gt; be a little careful with your arithmetic if you&#39;re used to math in C
&gt; or Java.&quot;

On the other hand (immediately after that paragraph):

&gt; &quot;In practice, integer values are treated as 32-bit ints (and are
&gt; stored that way in some browser implementations), which can be
&gt; important for bit-wise operations.&quot;

and

&gt; &quot;You can convert a string to an integer using the built-in parseInt()
&gt; function.&quot;

So, is there such thing as integer in JavaScript or isn&#39;t there?

  [1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/A_re-introduction_to_JavaScript

Is there or isn&#39;t there an integer type in JavaScript?

The C99 standard introduces the following datatypes. The documentation can be found [here][1] for the AVR stdint library.


 - `uint8_t` means it&#39;s an 8-bit unsigned type.
 - `uint_fast8_t`  means it&#39;s the fastest unsigned int with at least 8
   bits.
 - `uint_least8_t` means it&#39;s an unsigned int with at least 8 bits.

I understand `uint8_t` and what is `uint_fast8_t`( I don&#39;t know how it&#39;s implemented in register level).

1.Can you explain what is the meaning of &quot;it&#39;s an `unsigned int` with at least 8 bits&quot;? 

2.How `uint_fast8_t` and `uint_least8_t` help increase efficiency/code space compared to the `uint8_t`?


  [1]: http://www.nongnu.org/avr-libc/user-manual/group__avr__stdint.html#ga8f075c759c74e109e8184306c663809d

Difference between uint8_t, uint_fast8_t and uint_least8_t

    Integer i = 3; 
    i = i + 1; 
    Integer j = i; 
    j = i + j; 

How many objects are created as a result of the statements in the sample code above and why? Is there any IDE in which we can see how many objects are created (maybe in a debug mode)?


How many objects are created by using the Integer wrapper class?

I need to generate a random number. I found the [`Enum.random/1`](https://hexdocs.pm/elixir/Enum.html#random/1) function, but it expects an enumerable such as a list or range of numbers.

Is that the only way to get a random number?

How to generate a random number in Elixir?

I am using an `int` type to store a value. By the semantics of the program, the value always varies in a very small range (0 - 36), and `int` (not a `char`) is used only because of the CPU efficiency.

It seems like many special arithmetical optimizations can be performed on such a small range of integers. Many function calls on those integers might be optimized into a small set of &quot;magical&quot; operations, and some functions may even be optimized into table look-ups.

So, is it possible to tell the compiler that this `int` is always in that small range, and is it possible for the compiler to do those optimizations?


Can I hint the optimizer by giving the range of an integer?

I have a list, `a`:

    a = [&#39;a&#39;,&#39;b&#39;,&#39;c&#39;]

and need to duplicate some values with the suffix `_ind` added this way (order is important):

    [&#39;a&#39;, &#39;a_ind&#39;, &#39;b&#39;, &#39;b_ind&#39;, &#39;c&#39;, &#39;c_ind&#39;]

I tried:

    b = [[x, x + &#39;_ind&#39;] for x in a]
    c = [item for sublist in b for item in sublist]
    print (c)
    [&#39;a&#39;, &#39;a_ind&#39;, &#39;b&#39;, &#39;b_ind&#39;, &#39;c&#39;, &#39;c_ind&#39;]

Is there some better, more pythonic solution?

Content Type	Original Author	Original Content on Stackoverflow
Question	happyMOOyear	View Question on Stackoverflow
Solution 1 - C++	emlai	View Answer on Stackoverflow
Solution 2 - C++	Jordan Melo	View Answer on Stackoverflow

What does the integer suffix J mean?

C++ Problem Overview

C++ Solutions

Solution 1 - C++

Solution 2 - C++

Change data in migration Up method - Entity Framework

Difference between Stream Replication and logical replication

Attributions