In the Configuration Properties (`Project ➔ Properties`),

&quot;/ZI&quot; is in 

    C/C++ ➔ General ➔ Debug Information Format 

&quot;/Gy&quot; is in 

    C/C++ ➔ Code Generation ➔ Enable Function-Level Linking

You are choosing &quot;Edit and Continue&quot; (`/ZI`) to be able to fix code during debugging, but also &quot;Disable Function-Level Linking&quot; (`/Gy-`). 

Those two will not work together, as you cannot just change one function in the middle of the code. So just choose one of them, like changing `/Gy-` to `/Gy`.

*the same issue got, resolved by changing*  

Project ➔ Properties ➔ C/C++ ➔ General ➔ Debug Information Format ➔ Program Database (/Zi)

The [Boehm&#39;s conservative garbage collector][1] is quite useful (e.g. [Bigloo][2] is using it, [Guile][3] is using something similar, etc....), notably on Linux (which is the only OS I care about; I&#39;m using Debian/Sid/x86-64 if that matters, and `libgc-dev` package is version `1:7.4.2-8` so the Boehm GC is 7.4.2).

However, **Boehm&#39;s GC** requires to be aware of every thread using it. Its [gc_pthreads_redirects.h][4] (more or less internal) header file **is redefining `pthread_create`** as 

    # define pthread_create GC_pthread_create


Actually, what Boehm&#39;s GC needs is [GC_register_my_thread][5] to be called early in the new thread call stack (and `GC_pthread_create` is doing that).


In the past, Glib (2.46) provided a way to redefine memory allocation using [`struct GMemVTable` which is **deprecated**][6] **and cannot be used** anymore (my Debian&#39;s `libglib2.02.0-dev` package is version `2.50.3-2`). There is a [`g_mem_gc_friendly` global boolean][7] but when looking into Glib source code it simply clears memory zones before freeing them.

Recent GTK3 (my `libgtk-3-dev`  package has version `3.22.11-1`) are creating threads (for something probably related to Dbus, and perhaps also to GtkTextView...) using (indirectly) `pthread_create` thru [Glib thread functions][8]. And there is no way (except by patching the source code) to be notified of that thread creation. I&#39;m afraid than any GTK callback I would install (e.g. using [`g_signal_connect`][9]) might be called from these threads. Or that if I subclass a GTK widget with some methods which might use (or access) some `GC_malloc`-ed buffer there could be a disaster.

On the other hand, there is a strong coding rule in GTK that all GTK operations should happen only in the main thread. To quote [Gdk3 Threads][10] page:

&gt; **GTK+**, however, **is *not* thread safe**. You should only use GTK+ and GDK from the thread `gtk_init()` and `gtk_main()` were called on. This is usually referred to as the “main thread”.

If I follow this rule myself, I am sure that no internal GTK code will ever call my callbacks (using Boehm GC) from some non-main thread?

My intuition is that if ever `GC_alloc` is called from outside the main thread by GTK internals (not directly by my code) a disaster would happen
(because these GTK-internal threads have not been started with `GC_pthread_create`; there might call some of my code, e.g. because I am subclassing some existing GTK widget, or because I connected some GTK signal, even if I don&#39;t myself code things using GTK &amp; Boehm GC outside of the main thread.).

The point is that Boehm&#39;s GC needs to scan every stack in every thread possibly using it.

FWIW, I reported a possible [bug#780815][11] on GTK bugzilla.

A typical example is `gtk+-3.22.11/examples/application9/` from GTK-3.22.11 tarball. `pthread_create` [*is called*][12] very indirectly by `g_application_run` via `g_bus_get_sync`


  [1]: https://www.hboehm.info/gc/
  [2]: https://www-sop.inria.fr/indes/fp/Bigloo/
  [3]: http://www.gnu.org/software/guile
  [4]: https://github.com/ivmai/bdwgc/blob/master/include/gc_pthread_redirects.h#L80
  [5]: https://github.com/ivmai/bdwgc/blob/master/include/gc.h#L1393
  [6]: https://developer.gnome.org/glib/2.52/glib-Memory-Allocation.html#GMemVTable
  [7]: https://developer.gnome.org/glib/2.52/glib-Memory-Allocation.html#g-mem-gc-friendly
  [8]: https://developer.gnome.org/glib/2.52/glib-Threads.html
  [9]: https://developer.gnome.org/gobject/2.52/gobject-Signals.html#g-signal-connect
  [10]: https://developer.gnome.org/gdk3/stable/gdk3-Threads.html
  [11]: https://bugzilla.gnome.org/show_bug.cgi?id=780815
  [12]: https://bugzilla.gnome.org/page.cgi?id=traceparser/trace.html&amp;trace_id=237313

Is recent GTK 3.22 still Boehm GC friendly (thread issue)?

I found a rather strange but working square root approximation for `float`s; I really don&#39;t get it. Can someone explain me why this code works?

    float sqrt(float f)
    {
        const int result = 0x1fbb4000 + (*(int*)&amp;f &gt;&gt; 1);
        return *(float*)&amp;result;   
    }

I&#39;ve test it a bit and [it outputs values off of `std::sqrt()` by about 1 to 3%](http://coliru.stacked-crooked.com/a/568f0bd0fcf2838f). I know of the Quake III&#39;s [fast inverse square root](https://en.wikipedia.org/wiki/Fast_inverse_square_root) and I guess it&#39;s something similar here (without the newton iteration) but I&#39;d really appreciate an explanation of _how it works_.

(nota: I&#39;ve tagged it both [tag:c] and [tag:c++] since it&#39;s both valid-ish (see comments) C and C++ code)

How does this float square root approximation work?

I am having an issue with a project that I am working on. Despite the fact that the code is right, I can&#39;t build it because I got the following error

&gt;Error	D8016	&#39;/ZI&#39; and &#39;/Gy-&#39; command-line options are incompatible	LoadReport	C:\LoadReport\LoadReport\cl	

My version of the visual studio is 2015. Any idea would be appreciated.


Visual Studio error D8016: &#39;/ZI&#39; and &#39;/Gy&#39; command-line options are incompatible

I am having an issue with a project that I am working on. Despite the fact that the code is right, I can't build it because I got the following error
>Error	D8016	'/ZI' and '/Gy-' command-line options are incompatible	LoadReport	C:\LoadReport\LoadReport\cl
My version of the visual studio is 2015. Any idea would be appreciated.

I argued with a friend the other day about those two snippets. Which is faster and why ?

    value = 5;
    if (condition) {
        value = 6;
    }

and:

    if (condition) {
        value = 6;
    } else {
        value = 5;
    }

What if `value` is a matrix ?

Note: I know that `value = condition ? 6 : 5;` exists and I expect it to be faster, but it wasn&#39;t an option.

**Edit** (requested by staff since question is on hold at the moment):

 - please answer by considering either *x86 assembly* generated by mainstream compilers (*say g++, clang++, vc, mingw*) in both optimized and non optimized versions or *MIPS assembly*.
 - when assembly differ, explain why a version is faster and when (*e.g. &quot;better because no branching and branching has following issue blahblah&quot;*)

If statement vs if-else statement, which is faster?

Using GCC 6.3, the following C++ code:

    #include &lt;cmath&gt;
    #include &lt;iostream&gt;
    
    void norm(double r, double i)
    {
    	double n = std::sqrt(r * r + i * i);
    	std::cout &lt;&lt; &quot;norm = &quot; &lt;&lt; n;
    }

generates the following x86-64 assembly:

    norm(double, double):
            mulsd   %xmm1, %xmm1
            subq    $24, %rsp
            mulsd   %xmm0, %xmm0
            addsd   %xmm1, %xmm0
            pxor    %xmm1, %xmm1
            ucomisd %xmm0, %xmm1
            sqrtsd  %xmm0, %xmm2
            movsd   %xmm2, 8(%rsp)
            jbe     .L2
            call    sqrt
    .L2:
            movl    std::cout, %edi
            movl    $7, %edx
            movl    $.LC1, %esi
            call    std::basic_ostream&lt;char, std::char_traits&lt;char&gt; &gt;&amp; std::__ostream_insert&lt;char, std::char_traits&lt;char&gt; &gt;(std::basic_ostream&lt;char, std::char_traits&lt;char&gt; &gt;&amp;, char const*, long)
            movsd   8(%rsp), %xmm0
            movl    std::cout, %edi
            addq    $24, %rsp
            jmp     std::basic_ostream&lt;char, std::char_traits&lt;char&gt; &gt;&amp; std::basic_ostream&lt;char, std::char_traits&lt;char&gt; &gt;::_M_insert&lt;double&gt;(double)

For the call to `std::sqrt`, GCC first does it using `sqrtsd` and saves the result on to the stack. If it overflows, it then calls the libc `sqrt` function. But it never saves the `xmm0` after that and before the second call to `operator&lt;&lt;`, it restores the value from the stack (because `xmm0` was lost with the first call to `operator&lt;&lt;`).

With a simpler `std::cout &lt;&lt; n;`, it&#39;s even more obvious:

    subq    $24, %rsp
    movsd   %xmm1, 8(%rsp)
    call    sqrt
    movsd   8(%rsp), %xmm1
    movl    std::cout, %edi
    addq    $24, %rsp
    movapd  %xmm1, %xmm0
    jmp     std::basic_ostream&lt;char, std::char_traits&lt;char&gt; &gt;&amp; std::basic_ostream&lt;char, std::char_traits&lt;char&gt; &gt;::_M_insert&lt;double&gt;(double)

Why is GCC not using the `xmm0` value computed by libc `sqrt`?


Why does GCC call libc&#39;s sqrt() without using its result?

I have a project that currently uses C++11/14, but it requires something like `std::filesystem`, which is only available in C++17, and hence I don&#39;t have a chance to currently use it. I see, however, that it&#39;s available in my current compiler as `std::experimental::filesystem`. Is it a good idea to use experimental features, assuming that I could in the future add something like:

    #ifdef CXX17 //if this is C++17
    std::filesystem::something ...;
    #else
    std::experimental::filesystem::something ...;
    #endif

My concerns are:

**1. Is it guaranteed that all compliant compilers have the same experimental features?**

**2. Are experimental features prone to big changes that make them unreliable?**

Maybe there&#39;s more things to wonder about. Why should I or should I not use them? I&#39;m puzzled with a new project and don&#39;t know what to decide.


Are the experimental features of modern C++ reliable for long-term projects?

What is the difference between `if constexpr()` and `if()`?

Where and When can I use both of them?

Difference between &quot;if constexpr()&quot; Vs &quot;if()&quot;

Consider the following example:

    #include &lt;cstdlib&gt;

    int main() {
        const int m = 42;
        [] { m; }(); // OK

        const int n = std::rand();
        [] { n; }(); // error: &#39;n&#39; is not captured
    }

Why do I need to capture `n` in the second lambda but not `m` in the first lambda? I checked section 5.1.2 (_Lambda expressions_) in the C++14 standard but I was unable to find a reason. Can you point me to a paragraph in which this is explained?

Update: I observed this behavior with both GCC 6.3.1 and 7 (trunk). Clang 4.0 and 5 (trunk) fails with an error in both cases (`variable &#39;m&#39; cannot be implicitly captured in a lambda with no capture-default specified`).

Why is a const variable sometimes not required to be captured in a lambda?

ESlint static intellisense doesn&#39;t seem to be supported in Visual Studio 2017 which makes coding in .js files a complete pain as I have to run the CMD eslint command to get any linting errors. In VSCode I can just use the ESLint extension. What about Visual studio 2017?

Is their any way I can enable it?

ESLint support Visual studio 2017

I have a Resharper 9x license and it is only compatible up to MS VS Community 2015 edition. I tried to download the 2015 version from Microsoft but their website stubbornly wants me to have 2017, only. Can someone please provide me a url to the 2015 edition? Or, explain how to navigate Microsoft&#39;s site to obtain the 2015 edition?

**Update on solution**

1) vs_community.exe is the download filename for any version, 2015, 2017, etc. You will not know which version it is until you click the .exe. You will then see the version in the title of the installer.

2) There is a url trick to get the version that you want.

&lt;s&gt;https://www.visualstudio.com/thank-you-downloading-visual-studio/?sku=Community&amp;rel=15&lt;/s&gt;

...change the rel=15 to rel=17 etc

Or use the links provided in the answer below



How to download Visual Studio Community Edition 2015 (not 2017)

I am facing a strange issue from roslyn compiler. Sometimes when I build the solution I face a strange issue in error list which does not let me build the solution. Here is the error:

&gt;Severity	Code	Description	Project	File	Line	Suppression State
Error		Unable to copy file &quot;D:\Sealogical New Website\SealogicalWebsite\packages\Microsoft.Net.Compilers.1.0.0\tools\csc.exe&quot; to &quot;bin\roslyn\csc.exe&quot;. Access to the path &#39;bin\roslyn\csc.exe&#39; is denied.	SealogicalWebsite			

&gt;Severity	Code	Description	Project	File	Line	Suppression State
Error		Unable to copy file &quot;D:\Sealogical New Website\SealogicalWebsite\packages\Microsoft.Net.Compilers.1.0.0\tools\VBCSCompiler.exe&quot; to &quot;bin\roslyn\VBCSCompiler.exe&quot;. Access to the path &#39;bin\roslyn\VBCSCompiler.exe&#39; is denied.	SealogicalWebsite	

 1. I try to clean the solution and rebuild it but does not work again.
    
 2. Tried to delete files manually but again shows an error pointing out
    I do not have right permissions to do this:
    
 3. Tried deleting from `CMD` but again shows the same error:

[![Image when trying to delete files manually][1]][1]

The only way to delete roslyn generated files is by restarting the PC and when restarted I can delete them manually without a problem.

I am administrator in my PC so there is no problem with that I guess.

This problem seems to happen in Visual Studi0 2015 and Visual Studio 2017.

I dont like restarting the PC 4-5 times a day or more thats why I am asking here.

Some other details:

 - I am the one who created this project so theoretically it should not
   be a problem to do this action.
   
 - When the project first created I did run the Visual Studion in
   Administrator Mode as I am doing now.
 - I am using ASP.MVC 5 template in my project.
 - Files which do not get deleted are `bin/roslyn/csc` and `bin/roslyn/VBCSCompiler`.

I could find a solution to remove this part from web.config so it does not generate those files:


    &lt;compilers&gt;
      &lt;compiler language=&quot;c#;cs;csharp&quot; extension=&quot;.cs&quot; type=&quot;Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35&quot; warningLevel=&quot;4&quot; compilerOptions=&quot;/langversion:6 /nowarn:1659;1699;1701&quot; /&gt;
      &lt;compiler language=&quot;vb;vbs;visualbasic;vbscript&quot; extension=&quot;.vb&quot; type=&quot;Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35&quot; warningLevel=&quot;4&quot; compilerOptions=&quot;/langversion:14 /nowarn:41008 /define:_MYTYPE=\&amp;quot;Web\&amp;quot; /optionInfer+&quot; /&gt;
    &lt;/compilers&gt;

But this solution would cause problem with new c# 6 features so I can not remove this section.....

Furthermore I tried this command in CMD to see if there is a process locking this file but anyway it did not show me any process at all:

    C:\WINDOWS\system32&gt;tasklist /m D:\SealogicalNewWebsite\SealogicalWebsite\SealogicalWebsite\bin\roslyn\csc.exe
    INFO: No tasks are running which match the specified criteria.

Does anybody knows a way how to handle this strange issue ?


  [1]: https://i.stack.imgur.com/XUcwF.png

Can not delete \bin\roslyn\VBCSCompiler.exe - Access is denied

For some reason, even so much as typing this into a C# file in Visual Studio is enough to cause it to instantly crash. Why?

    unsafe struct node {
        node*[] child;
    }

It seems to occur when the IDE would start coloring keywords and the like.

Trying it in TIO spits out `csc.exe exited with code 1` which isn&#39;t very helpful.

While array declarations in C# are different than in C/C++, the above &lt;i&gt;seems&lt;/i&gt; like it should be perfectly valid. Why isn&#39;t it, and why does it crash Visual Studio?

My Visual Studio version is 14.0.23107.

Content Type	Original Author	Original Content on Stackoverflow
Question	dim mik	View Question on Stackoverflow
Solution 1 - C++	Pierre	View Answer on Stackoverflow
Solution 2 - C++	Bo Persson	View Answer on Stackoverflow
Solution 3 - C++	N.SANDEEP REDDY sandeep	View Answer on Stackoverflow

Visual Studio error D8016: '/ZI' and '/Gy' command-line options are incompatible

C++ Problem Overview

C++ Solutions

Solution 1 - C++

Solution 2 - C++

Solution 3 - C++

How does this float square root approximation work?

Is recent GTK 3.22 still Boehm GC friendly (thread issue)?

Attributions