If running Ubuntu,

The recommended way to enable the needed ptrace kernel setting (hinted by qtcreator) is to edit  /etc/sysctl.d/10-ptrace.conf

    sudo vim  /etc/sysctl.d/10-ptrace.conf

Then change

    kernel.yama.ptrace_scope = 1
to

    kernel.yama.ptrace_scope = 0

Save,

then apply:

    $ sudo sysctl --system -a -p|grep yama
    kernel.yama.ptrace_scope = 0

run

    man sysctl

for more info.

I got the answer. 

 - Go to the location `/etc` with root privilege. 
   
 - Find the file `rc.local`.
 - Open it in a text editor like gedit and add the following    code
   there   
 - `echo 0 | tee /proc/sys/kernel/yama/ptrace_scope`

Restart your pc and you can see the debugger working perfectly.


I found the answer that works for me on ubuntu in below link and the credit goes to [dstzcxr][1]

[https://askubuntu.com/a/501271/395583][2]

&gt; Just uncheck (or check - run - uncheck if it is for some reason
&gt; unchecked) the box &quot;Run in terminal&quot; in &quot;Projects&quot; (on the left bar) -
&gt; &quot;Run&quot; tab - &quot;Run&quot; section.


  [1]: https://askubuntu.com/users/298229/dstzcxr
  [2]: https://askubuntu.com/a/501271/395583

I&#39;m new-ish to Ruby and Rails.  I am looking for a purely objective list of features and advantages/disadvantages of each.  In an effort to keep preference out of this, please refrain from answering unless you have used all 3 systems. 

What are the differences between rbenv, rvm, and chruby?

I&#39;m having trouble adding a line break in SSRS 2008.

I&#39;ve tried all of these different ways but nothing is doing it.

`&quot;+ chr(10) +&quot; , &quot;&amp; chr(10) &amp;&quot; , &quot;&amp; chr(13) &amp; chr(10) &amp;&quot; , &quot;&amp; vbcrlf &amp;&quot; , &quot;+ vbcrlf +&quot; , &quot;Environment.NewLine&quot;`

Here&#39;s my `textbox` expression:

    =IIF(First(Fields!VCHTYPE.Value, &quot;Dataset1&quot;)=&quot;C&quot;,&quot;This is a huge paragrpah of text.&quot; +
    vbcrlf + &quot;separated by line feeds at each paragraph.&quot; +
    vbcrlf + vbcrlf + &quot;I want to separate the paragraphs.&quot; +
    vbcrlf + vbcrlf + &quot;Its not working though.&quot;
    , &quot;This is the second huge paragraph of text.&quot; +
    vbcrlf + &quot;separated by line feeds at each paragraph.&quot; +
    vbcrlf + vbcrlf + &quot;I want to separate the paragraphs.&quot; +
    vbcrlf + vbcrlf + &quot;Its not working though.&quot; )

Line break in SSRS expression

While debugging `C++` code in Qt creator I get the following error

    ptrace: Operation not permitted.
    
    Could not attach to the process. Make sure no other debugger traces this process.
    Check the settings of
    /proc/sys/kernel/yama/ptrace_scope
    For more details, see /etc/sysctl.d/10-ptrace.conf

Here a temporary solution is found: [Receiving error while trying to debug in QtProject][1]

 - temporary solution (won&#39;t survive a reboot):

     `echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope`


But it is difficult to run the same code in terminal every time when I start my PC to use Qt. 

    What is the permanent solution for this?

  [1]: https://askubuntu.com/questions/244336/receiving-error-while-trying-to-debug-in-qtproject


Qt Creator, ptrace: Operation not permitted. What is the permanent solution?

While debugging <code>C++</code> code in Qt creator I get the following error
<pre><code class="hljs language-arduino">ptrace: Operation not permitted.

Could not attach to the process. Make sure no other debugger traces this process.
Check the settings of
/proc/sys/kernel/yama/ptrace_scope
For more details, see /etc/sysctl.d/10-ptrace.conf
</code></pre>
Here a temporary solution is found: <a href="https://askubuntu.com/questions/244336/receiving-error-while-trying-to-debug-in-qtproject" target="_blank" rel="noopener noreferrer">Receiving error while trying to debug in QtProject</a>
<ul>
<li>
temporary solution (won't survive a reboot):
<code>echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope</code>
</li>
</ul>
But it is difficult to run the same code in terminal every time when I start my PC to use Qt.
<pre><code class="hljs language-kotlin">What is the permanent solution for this?
</code></pre>

I&#39;m coming from a Java background and have started working with objects in C++. But one thing that occurred to me is that people often use pointers to objects rather than the objects themselves, for example this declaration:

    Object *myObject = new Object;

rather than:

    Object myObject;

Or instead of using a function, let&#39;s say `testFunc()`, like this:

    myObject.testFunc();

we have to write:

    myObject-&gt;testFunc();

But I can&#39;t figure out why should we do it this way. I would assume it has to do with efficiency and speed since we get direct access to the memory address. Am I right?


Why should I use a pointer rather than the object itself?

My question is that

I have a size_t data, but now I want to convert it to double or int.

If I do something like 

     size_t data = 99999999;
     int convertdata = data;

the compiler will report warning. because it maybe overflow.

Do you have some method like the boost or some other method to do the convert?


How to cast the size_t to double or int C++

What are undeclared identifier errors? What are common causes and how do I fix them?

Example error texts:

 * For the Visual Studio compiler: `error C2065: &#39;cout&#39; : undeclared identifier`
 * For the GCC compiler: `&#39;cout&#39; undeclared (first use in this function)`


What is an &#39;undeclared identifier&#39; error and how do I fix it?

I&#39;m very new to C++ and struggling to figure out how I should iterate through a list of objects and access their members.

I&#39;ve been trying this where `data` is a `std::list` and `Student` a class.

    std::list&lt;Student&gt;::iterator&lt;Student&gt; it;
	for (it = data.begin(); it != data.end(); ++it) {
	    std::cout&lt;&lt;(*it)-&gt;name;
	}

and getting the following error:
    
    error: base operand of ‘-&gt;’ has non-pointer type ‘Student’

How to iterate through a list of objects in C++?

As per the title. I don&#39;t want to download the entire Visual C++ installer, only &quot;cl.exe&quot; and the other programs required for compiling and linking C++ programs on Windows.

Can I download the Visual C++ Command Line Compiler without Visual Studio?

I am using Qt Designer, and I would like to move a couple of top-level widgets into a horizontal layout.

I have dragged a &quot;Horizontal Layout&quot; object into the form.  I am now attempting to drag the desired widgets into the layout.

Unfortunately, the new Horizontal Layout widget is infinitely thin:

![Infinitely Thin Layout][1]

... and I cannot drag my &quot;Import Progress&quot; label widget or my progress bar widget into the new horizontal layout widget.

Note that when I attempt to drag the desired widgets over the new horizontal layout widget, Qt Designer does not do anything useful for me in terms of expanding the drop region to make the horizontal widget available as a drop target.  So I&#39;m stuck.

How do I add widgets to an infinitely-thin layout widget in Qt Designer?


  [1]: http://i.stack.imgur.com/Tzhvk.jpg

Qt designer: How to add widget to a layout in the designer when the layout appears infinitely thin?

I use Python 3 and PyQt5. Here&#39;s my test PyQt5 program, focus on the last 2 lines:

    from PyQt5.QtCore import *
    from PyQt5.QtWidgets import *
    import sys

    class window(QWidget):
	def __init__(self,parent=None):
		super().__init__(parent)
		self.setWindowTitle(&#39;test&#39;)
		self.resize(250,200)

    app=QApplication(sys.argv)
    w=window()
    w.show()
    sys.exit(app.exec())
    #sys.exit(app.exec_())

I know `exec` is a language keyword in Python. But code on [Official PyQt5 Documentation][1] *(specifically the **Object Destruction on Exit** part)*. I see that example shows use of `app.exec()` which confuses me.

When I tested it on my machine. I found there is no any visible difference from my end. Both with and without `_` produces the same output in no time difference.

My question is:

 - Is there anything wrong going when I use `app.exec()`? like clashing with Python&#39;s internal `exec`? I suspect because both `exec`&#39;s are executing something.
 - If not, can I use both interchangeably?

  [1]: http://pyqt.sourceforge.net/Docs/PyQt5/pyqt4_differences.html#object-destruction-on-exit

Should I use `app.exec()` or `app.exec_()` in my PyQt application?

I wanted to know if there is a way to do a silent install of the Qt run installer on Ubuntu Server?  
I mean by-pass the options of the installer and do a default install?

Silent install Qt run installer on ubuntu server

PIMPL stands for **P**ointer to **IMPL**ementation. The implementation stands for &quot;implementation detail&quot;: something that the users of the class need not to be concerned with.

Qt&#39;s own class implementations cleanly separate out the interfaces from the implementations through the use of the PIMPL idiom. Yet, the mechanisms provided by Qt are undocumented. How to use them?

I&#39;d like this to be the canonical question about &quot;how do I PIMPL&quot; in Qt. The answers are to be motivated by a simple coordinate entry dialog interface shown below.

The motivation for the use of PIMPL becomes apparent when we have anything with a semi-complex implementation. Further motivation is given in [this question][1]. Even a fairly simple class has to pull in a lot of other headers in its interface.

![dialog screenshot][2]

The PIMPL-based interface is fairly clean and readable. 

    // CoordinateDialog.h
    #include &lt;QDialog&gt;
    #include &lt;QVector3D&gt;
    
    class CoordinateDialogPrivate;
    class CoordinateDialog : public QDialog
    {
      Q_OBJECT
      Q_DECLARE_PRIVATE(CoordinateDialog)
    #if QT_VERSION &lt;= QT_VERSION_CHECK(5,0,0)
      Q_PRIVATE_SLOT(d_func(), void onAccepted())
    #endif
      QScopedPointer&lt;CoordinateDialogPrivate&gt; const d_ptr;
    public:
      CoordinateDialog(QWidget * parent = 0, Qt::WindowFlags flags = 0);
      ~CoordinateDialog();
      QVector3D coordinates() const;
      Q_SIGNAL void acceptedCoordinates(const QVector3D &amp;);
    };
    Q_DECLARE_METATYPE(QVector3D)

A Qt 5, C++11 based interface doesn&#39;t need the `Q_PRIVATE_SLOT` line.

Compare that to a non-PIMPL interface that tucks implementation details into the private section of the interface. Note how much other code has to be included.

    // CoordinateDialog.h
    #include &lt;QDialog&gt;
    #include &lt;QVector3D&gt;
    #include &lt;QFormLayout&gt;
    #include &lt;QDoubleSpinBox&gt;
    #include &lt;QDialogButtonBox&gt;
    
    class CoordinateDialog : public QDialog
    {
      QFormLayout m_layout;
      QDoubleSpinBox m_x, m_y, m_z;
      QVector3D m_coordinates;
      QDialogButtonBox m_buttons;
      Q_SLOT void onAccepted();
    public:
      CoordinateDialog(QWidget * parent = 0, Qt::WindowFlags flags = 0);
      QVector3D coordinates() const;
      Q_SIGNAL void acceptedCoordinates(const QVector3D &amp;);
    };
    Q_DECLARE_METATYPE(QVector3D)

Those two interfaces are *exactly equivalent* as far as their public interface is concerned. They have the same signals, slots and public methods.

  [1]: https://stackoverflow.com/q/8972588/1329652
  [2]: http://i.stack.imgur.com/DshC2.png

How to use the Qt&#39;s PIMPL idiom?

I have seen references to all three of these applications on various parts of the Qt website but am completely unclear as to the exact differences between them and whether they are actually separate things or just different names for the same thing, or the name changed over time? Or is one no longer supported? What&#39;s the deal with these?


Qt Designer vs Qt Quick Designer vs Qt Creator?

What is the difference between them?

I know that u-boot needs a kernel in uImage format.

The system I use first boots from stage 1 loader and then it calls u-boot. I want to discard u-boot and directly boot from stage 1 loader. Which type of kernel image do I have to use? 

Image vs zImage vs uImage

I need to write an SPI Linux character device driver for omap4 from scratch.
I know some basics of writing device drivers. But, I don&#39;t know how to start writing platform specific device driver from scratch.

I&#39;ve written some basic char drivers, and I thought writing SPI device driver would be similar to it. Char drivers have a structure `file_operations` which contains the functions implemented in the driver.

    struct file_operations Fops = {
    	.read = device_read,
    	.write = device_write,
    	.ioctl = device_ioctl,
    	.open = device_open,
    	.release = device_release,	/* a.k.a. close */
    };

Now, I am going through [spi-omap2-mcspi.c][1] code as a reference to get an idea to start developing SPI driver from scratch.

But, I don&#39;t see functions such as open, read, write etc.
Don&#39;t know from where the program starts.


  [1]: http://lxr.free-electrons.com/source/drivers/spi/spi-omap2-mcspi.c

How to write a simple Linux device driver?

I read a paper and it used terms **cold cache** and **warm cache**. I googled about this terms but I didn&#39;t find something useful (only a thread [here][1]). 

What do these terms mean? 



  [1]: https://web.archive.org/web/20150420002300/http://help.lockergnome.com/linux/Cold-cache-warm-cache--ftopict414393.html

What does it mean by cold cache and warm cache concept?

It&#39;s a question which has been asked many times, however there is no well supported answer I could find.

Many people suggest the use of top command, but if you run top once (because you have a script for example collecting Cpu usage every 1 second) it will always give the same Cpu usage result ([example 1][1], [example 2][2]).

A more accurate way to calculate CPU usage, is by reading the values from `/proc/stat`, but most of the answers use only the first 4 fields from `/proc/stat` to calculate it (one example [here][2]).

`/proc/stat/` has 10 fields per CPU core as of Linux kernel 2.6.33!

I also found this https://stackoverflow.com/questions/5514119/accurately-calculating-cpu-utilization-in-linux-using-proc-stat question which is pointing out the same issue, -that most other questions only take into consideration 4 out of the many fields- but still the answer given here starts with &quot;I think&quot; (not certain), and except that, it is only concerned about the first 7 fields (out of 10 in `/proc/stat/`)

[This][3] perl script uses all of the fields to calculate the CPU usage, which again I do not think is correct after some further investigation.

After taking a quick look into the kernel code [here][4], it looks like, for example, `guest_nice` and `guest fields` are always increasing together with `nice` and `user` (so they should not be included in the cpu usage calculation, since they are included in `nice` and `user` fields already)

    /*
     * Account guest cpu time to a process.
     * @p: the process that the cpu time gets accounted to
     * @cputime: the cpu time spent in virtual machine since the last update
     * @cputime_scaled: cputime scaled by cpu frequency
     */
    static void account_guest_time(struct task_struct *p, cputime_t cputime,
    			       cputime_t cputime_scaled)
    {
    	u64 *cpustat = kcpustat_this_cpu-&gt;cpustat;
    
    	/* Add guest time to process. */
    	p-&gt;utime += cputime;
    	p-&gt;utimescaled += cputime_scaled;
    	account_group_user_time(p, cputime);
    	p-&gt;gtime += cputime;
    
    	/* Add guest time to cpustat. */
    	if (task_nice(p) &gt; 0) {
    		cpustat[CPUTIME_NICE] += (__force u64) cputime;
    		cpustat[CPUTIME_GUEST_NICE] += (__force u64) cputime;
    	} else {
    		cpustat[CPUTIME_USER] += (__force u64) cputime;
    		cpustat[CPUTIME_GUEST] += (__force u64) cputime;
    	}
    }

So to sum up, what is an accurate way to calculate the CPU usage in Linux and which fields should be considered in the calculations and how (which fields are attributed to the idle time and which fields to non-idle time)?


  [1]: https://unix.stackexchange.com/questions/69185/getting-cpu-usage-same-every-time
  [2]: https://unix.stackexchange.com/questions/27076/how-can-i-receive-top-like-cpu-statistics-from-the-shell
  [3]: https://gist.github.com/creaktive/781248
  [4]: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/kernel/sched/cputime.c?h=v4.8#n169

Accurate calculation of CPU usage given in percentage in Linux?

    KDIR ?= $(shell uname -r)

What is the meaning of `?=`?

I have understood the difference between `:=`, `+=` and `=` from another thread available in Stack Overflow, but unable to find the explanation for `?=`.

What is ?= in Makefile

I see there is a new class for regular expressions - `QRegularExpression`. Is it just a typedef for QRegExp, or a new class, or what? And why do we need it, we already have QRegExp?

Is there any difference between QRegularExpression and QRegExp?

I&#39;ve added languages in Language Support but I do not see the language icon in the panel tray, nor can I switch between languages.

How does one add keyboard languages and switch between them in Linux Mint 16?

I just followed the tutorial located at https://www.digitalocean.com/community/articles/how-to-install-linux-apache-mysql-php-lamp-stack-on-ubuntu while fixing multiple other errors that I came across along the way and I&#39;m stuck with one last error. When I log in to phpMyAdmin, there&#39;s a huge red error at the bottom saying &quot;The mcrypt extension is missing. Please check your PHP configuration.&quot;.
I installed everything listed in the tutorial on Ubuntu 13.10 via putty.

The mcrypt extension is missing. Please check your PHP configuration

I have PostgreSQL `9.3` and `9.4` installed on my ***Linux Mint*** machine. 

***How can I restart PostgreSQL 9.4?*** 

A method to restart both versions together is also fine. 

How to restart Postgresql

I&#39;m trying to execute a [Python script](https://pastebin.com/jSjn1aaD), but I am getting the following error:

    Process finished with exit code 139 (interrupted by signal 11: SIGSEGV)

I&#39;m using python 3.5.2 on a Linux Mint 18.1 Serena OS

Can someone tell me why this happens, and how can I solve?


Content Type	Original Author	Original Content on Stackoverflow
Question	Indra	View Question on Stackoverflow
Solution 1 - C++	xor007	View Answer on Stackoverflow
Solution 2 - C++	Indra	View Answer on Stackoverflow
Solution 3 - C++	eSadr	View Answer on Stackoverflow

Qt Creator, ptrace: Operation not permitted. What is the permanent solution?

C++ Problem Overview

C++ Solutions

Solution 1 - C++

Solution 2 - C++

Solution 3 - C++

Line break in SSRS expression

What are the differences between rbenv, rvm, and chruby?

Attributions