Use `nm` to see all symbols and `c++filt` to demangle.

Example:

    nm -an foo | c++filt

The profiling tool I use already knows the symbols and source code, [since it is just the debugger][1]. I can build the app with symbols included, even with full optimization.


  [1]: https://stackoverflow.com/questions/375913/what-can-i-use-to-profile-c-code-in-linux/378024#378024

Say I have the following :

    var a = $(&quot;#a&quot;);
    var b = $(&quot;#b&quot;);
    
    //I want to do something as such as the following : 

    $(a,b).click(function () {/* */}); // &lt;= does not work

    //instead of attaching the handler to each one separately

Obviously the above does not work because in the `$` function, the second argument is the [`context`][1], not another element.

So how can I attach the event to both the elements at one go ?


----------

**[Update]**

[peirix][2] posted an interesting snippet in which he combines elements with the `&amp;` sign; But something I noticed this : 

    $(a &amp; b).click(function () { /* */ }); // &lt;= works (event is attached to both)

    $(a &amp; b).attr(&quot;disabled&quot;, true); // &lt;= doesn&#39;t work (nothing happens)

From what you can see above, apparently, the combination with the `&amp;` sign works only when attaching events...?


  [1]: http://docs.jquery.com/Core/jQuery#expressioncontext
  [2]: https://stackoverflow.com/questions/1388018/jquery-attaching-an-event-to-multiple-elements-at-one-go/1388087#1388087

Attaching an event to multiple elements at one go

Why are some exceptions in Java not caught by `catch (Exception ex)`?  This is code is completely failing out with an unhandled exception.  (Java Version 1.4).

	public static void main(String[] args) {
		try {
			//Code ...
		} catch (Exception ex) {
            System.err.println(&quot;Caught Exception&quot;);
			ex.printStackTrace();
			exitCode = app.FAILURE_EXIT_CODE;
		}
		finally {
			app.shutdown();
		}
		System.exit(exitCode);
	}

I get a `Exception in thread &quot;main&quot; java.lang.NoSuchMethodError`

But this works

	public static void main(String[] args) {
		int exitCode = app.SUCCESS_EXIT_CODE;
		try {
			//Code ...
		} catch (java.lang.NoSuchMethodError mex){
			System.err.println(&quot;Caught NoSuchMethodError&quot;);
			mex.printStackTrace();
			exitCode = app.FAILURE_EXIT_CODE;
		} catch (Exception ex) {
            System.err.println(&quot;Caught Exception&quot;);
			ex.printStackTrace();
			exitCode = app.FAILURE_EXIT_CODE;
		}
		finally {
			app.shutdown();
		}
		System.exit(exitCode);
	}

I get `Caught NoSuchMethodError java.lang.NoSuchMethodError: `

I thought catching exceptions would catch all exceptions?  How can I catch all exceptions in java?


Java exception not caught

Which tools do you guys use? How do demangle c++ symbols do be able to pass it to profiler tools, such as [opannotate][1]?

Thanks


  [1]: http://oprofile.sourceforge.net/doc/opannotate.html

How can I see symbols of (C and C++) binary on linux?

<p>Which tools do you guys use? How do demangle c++ symbols do be able to pass it to profiler tools, such as <a href="http://oprofile.sourceforge.net/doc/opannotate.html" target="_blank" rel="noopener noreferrer">opannotate</a>?</p>
<p>Thanks</p>


It seems that many projects slowly come upon a need to do matrix math, and fall into the trap of first building some vector classes and slowly adding in functionality until they get caught building a half-assed custom linear algebra library, and depending on it. 

I&#39;d like to avoid that while not building in a dependence on some tangentially related library (e.g. OpenCV, OpenSceneGraph). 

What are the commonly used matrix math/linear algebra libraries out there, and why would decide to use one over another? Are there any that would be advised against using for some reason? I am specifically using this in a geometric/time context*(2,3,4 Dim)* but may be using higher dimensional data in the future. 

I&#39;m looking for differences with respect to any of: API, speed, memory use, breadth/completeness, narrowness/specificness, extensibility, and/or maturity/stability.

Update
---

I ended up using Eigen3 which I am extremely happy with.


What are the most widely used C++ vector/matrix math/linear algebra libraries, and their cost and benefit tradeoffs?

How does one go about sorting a vector containing custom (i.e. user defined) objects.  
Probably, standard STL algorithm **sort** along with a predicate (a function or a function object) which would operate on one of the fields (as a key for sorting) in the custom object should be used.  
Am I on the right track?

Sorting a vector of custom objects

I&#39;ve got a fstream my_file(&quot;test.txt&quot;), but I don&#39;t know if test.txt exists. In case it exists, I would like to know if I can read it, too. How to do that?

*I use Linux.*

How to check if a file exists and is readable in C++?

Reading some questions here on SO about conversion operators and constructors got me thinking about the interaction between them, namely when there is an &#39;ambiguous&#39; call. Consider the following code:

    class A;
    
    class B { 
          public: 
             B(){} 
             
             B(const A&amp;) //conversion constructor
             { 
                  cout &lt;&lt; &quot;called B&#39;s conversion constructor&quot; &lt;&lt; endl; 
             } 
    };
    
    class A { 
          public: 
             operator B() //conversion operator
             { 
                  cout &lt;&lt; &quot;called A&#39;s conversion operator&quot; &lt;&lt; endl; 
                  return B(); 
             } 
    };
    
    int main()
    {
        B b = A(); //what should be called here? apparently, A::operator B()
        return 0;
    }

The above code displays &quot;called A&#39;s conversion operator&quot;, meaning that the conversion operator is called as opposed to the constructor. If you remove/comment out the `operator B()` code from `A`, the compiler will happily switch over to using the constructor instead (with no other changes to the code). 

My questions are:

 1. Since the compiler doesn&#39;t consider `B b = A();` to be an ambiguous call, there must be some type of precedence at work here. Where exactly is this precedence established? (a reference/quote from the C++ standard would be appreciated)
 2. From an object-oriented philosophical standpoint, is this the way the code should behave? Who knows more about how an `A` object should become a `B` object, `A` or `B`? According to C++, the answer is `A` -- is there anything in object-oriented practice that suggests this should be the case? To me personally, it would make sense either way, so I&#39;m interested to know how the choice was made.

Thanks in advance

Conversion constructor vs. conversion operator: precedence

After a Windows API call, how can I get the last error message in a textual form?

`GetLastError()` returns an integer value, not a text message.


How to get the error message from the error code returned by GetLastError()?

I came across these two methods to concatenate strings:

Common part:

    char* first= &quot;First&quot;;
    char* second = &quot;Second&quot;;
    char* both = malloc(strlen(first) + strlen(second) + 2);

Method 1:

    strcpy(both, first);
    strcat(both, &quot; &quot;);       // or space could have been part of one of the strings
    strcat(both, second);

Method 2:

    sprintf(both, &quot;%s %s&quot;, first, second);

In both cases the content of &lt;code&gt;both&lt;/code&gt; would be &lt;code&gt;&quot;First Second&quot;&lt;/code&gt;.

I would like to know which one is more efficient (I have to perform several concatenation operations), or if you know a better way to do it.


Concatenating strings in C, which method is more efficient?

I want to learn more about using the [SSE](http://en.wikipedia.org/wiki/Streaming_SIMD_Extensions).

What ways are there to learn, besides the obvious reading the [Intel&#174; 64 and IA-32 Architectures Software Developer&#39;s Manuals](http://www.intel.com/products/processor/manuals/)?

Mainly I&#39;m interested to work with the [GCC X86 Built-in Functions](http://gcc.gnu.org/onlinedocs/gcc-4.4.1/gcc/X86-Built_002din-Functions.html#X86-Built_002din-Functions).

Getting started with Intel x86 SSE SIMD instructions

I was facing this unique problem of generating a bit-mask based on the input parameter. For example,

if param = 2, then the mask will be 0x3  (11b)
if param = 5, then the mask will be 0x1F (1 1111b)

This I implemented using a for-loop in C, something like

    int nMask = 0;
    for (int i = 0; i &lt; param; i ++) {
    
        nMask |= (1 &lt;&lt; i);
    }

I would like to know if there is a better algorithm ~~~

Algorithm to generate bit mask

Why is `sizeof` considered an operator and not a function?

What property is necessary to qualify as an operator?


Why is sizeof considered an operator?

I&#39;ve always avoided Java reflection soley based on its reputation for slowness. I reached a point in the design of my current project where being able to use it would make my code much more readable and elegant, so I decided to give it a go. 

I was simply astonished by the difference, I noticed at times almost 100x longer run times. Even in this simple example where it just instantiates an empty class, it&#39;s unbelievable.

    class B {
    	
    }
    
    public class Test {
    	
    	public static long timeDiff(long old) {
    		return System.currentTimeMillis() - old;
    	}
    	
    	public static void main(String args[]) throws Exception {
    		
    		long numTrials = (long) Math.pow(10, 7);
    		
    		long millis;
    		
    		millis = System.currentTimeMillis();
    		
    		for (int i=0; i&lt;numTrials; i++) {
    			new B();
    		}
    		System.out.println(&quot;Normal instaniation took: &quot;
                     + timeDiff(millis) + &quot;ms&quot;);
    		
    		millis = System.currentTimeMillis();
    		
    		Class&lt;B&gt; c = B.class;
    		
    		for (int i=0; i&lt;numTrials; i++) {
    			c.newInstance();
    		}
    		
    		System.out.println(&quot;Reflecting instantiation took:&quot; 
                  + timeDiff(millis) + &quot;ms&quot;);
    		
    	}
    }

So really, my questions are

 - Why is it this slow? Is there something I&#39;m doing wrong? (even the example above demonstrates the difference). I have a hard time believing that it can really be 100x slower than normal instantiation.

 - Is there something else that can be better used for treating code as Data (bear in mind I&#39;m stuck with Java for now)



Java Reflection: Why is it so slow?

Does it actually matter which CDN you use to link to your jquery file or any javascript file for that matter.  Is one potentially faster than the other?  What other factors could play a role in which cdn you decide to use?  I know that Microsoft, Yahoo, and Google all have CDN&#39;s now.

Microsoft CDN for jQuery or Google CDN?

We have a table with a composite Primary key consisting of three fields (and it is in MySQL 5.1). There are near 200 inserts and 200 selects per second on this table, and the size of the table is around 1 million rows and it is increasing. 

My question is: does the &quot;Composite Primary Key&quot; decrease the performance of the Inserts and Selects on this table? 

Should I be using a simple Auto-Increasing INT ID field instead of a Composite Primary Key? (I think the answer is very much related to the way MySQL handles the Indexes on multiple columns)

Composite Primary Key performance drawback in MySQL

Is there a better way of doing a query like this:

    SELECT COUNT(*) 
    FROM (SELECT DISTINCT DocumentId, DocumentSessionId
          FROM DocumentOutputItems) AS internalQuery

I need to count the number of distinct items from this table but the distinct is over two columns.

My query works fine but I was wondering if I can get the final result using just one query (without using a sub-query)

Counting DISTINCT over multiple columns

I want to limit the maximum memory used by the JVM. Note, this is not just the heap, I want to limit the total memory used by this process.

How to set the maximum memory usage for JVM?

I&#39;m looking to find bottlenecks in my Java application in [Eclipse][1]. I&#39;m thinking this might be useful:

http://www.eclipse.org/projects/project_summary.php?projectid=tptp.performance

Any other good plug-ins to use?

**EDIT** OK, it doesn&#39;t necessarily have to be an Eclipse plug-in. But it would be nice. And, I&#39;m most interested in speed.

  [1]: http://en.wikipedia.org/wiki/Eclipse_(software)


Profiling a Java Application in Eclipse? (plug-in)

I’ve got a lot of plugins enabled when using Vim – I have collected plugins over the years.  I’m a bit fed up with how long Vim takes to start now, so I’d like to profile its startup and see which of the many plugins I have are responsible.

Is there any way to profile Vim’s startup or script-running?  Ideally I’d like to know how long Vim spends in each Vim script it loads.


Profiling Vim startup time

I&#39;m experimenting with [MATLAB][1] [OOP][2], as a start I mimicked my C++&#39;s Logger classes and I&#39;m putting all my string helper functions in a String class, thinking it would be great to be able to do things like `a + b`, `a == b`, `a.find( b )` instead 
of `strcat( a b )`, `strcmp( a, b )`, retrieve first element of `strfind( a, b )`, etc.

**The problem: slowdown**

I put the above things to use and immediately noticed a *drastic* slowdown. Am I doing it wrong (which is certainly possible as I have rather limited MATLAB experience), or does MATLAB&#39;s OOP just introduce a lot of overhead?

**My test case**

Here&#39;s the simple test I did for string, basically just appending a string and removing the appended part again:

&gt; Note: Don&#39;t actually write a String class like this in real code! Matlab has a native `string` array type now, and you should use that instead.

    classdef String &lt; handle
      ....
      properties
        stringobj = &#39;&#39;;
      end
      function o = plus( o, b )
        o.stringobj = [ o.stringobj b ];
      end
      function n = Length( o )
        n = length( o.stringobj );
      end
      function o = SetLength( o, n )
        o.stringobj = o.stringobj( 1 : n );
      end
    end

    function atest( a, b ) %plain functions
      n = length( a );
      a = [ a b ];
      a = a( 1 : n );

    function btest( a, b ) %OOP
      n = a.Length();
      a = a + b;
      a.SetLength( n );

    function RunProfilerLoop( nLoop, fun, varargin )
      profile on;
      for i = 1 : nLoop
        fun( varargin{ : } );
      end
      profile off;
      profile report;

    a = &#39;test&#39;;
    aString = String( &#39;test&#39; );
    RunProfilerLoop( 1000, @(x,y)atest(x,y), a, &#39;appendme&#39; );
    RunProfilerLoop( 1000, @(x,y)btest(x,y), aString, &#39;appendme&#39; );

**The results**

Total time in seconds, for 1000 iterations:

&gt; btest 0.550 (with String.SetLength 0.138, String.plus 0.065, String.Length 0.057)
&gt;
&gt; atest 0.015

Results for the logger system are likewise: 0.1 seconds for 1000 calls 
to `frpintf( 1, &#39;test\n&#39; )`, 7 (!) seconds for 1000 calls to my system when using the String class internally (OK, it has a lot more logic in it, but to compare with C++: the overhead of my system that uses `std::string( &quot;blah&quot; )` and `std::cout` at the output side vs plain `std::cout &lt;&lt; &quot;blah&quot;` is on the order of 1 millisecond.)

**Is it just overhead when looking up class/package functions?**

Since MATLAB is interpreted, it has to look up the definition of a function/object at run time. So I was wondering that maybe much more overhead is involved in looking up class or package function vs functions that are in the path. I tried to test this, and it just gets stranger. To rule out the influence of classes/objects, I compared calling a function in the path vs a function in a package:

    function n = atest( x, y )
      n = ctest( x, y ); % ctest is in matlab path
    
    function n = btest( x, y )
      n = util.ctest( x, y ); % ctest is in +util directory, parent directory is in path

Results, gathered same way as above:

&gt; atest 0.004 sec, 0.001 sec in ctest
&gt;
&gt; btest 0.060 sec, 0.014 sec in util.ctest


So, is all this overhead just coming from MATLAB spending time looking up definitions for its OOP implementation, whereas this overhead is not there for functions that are directly in the path?

  [1]: http://en.wikipedia.org/wiki/MATLAB
  [2]: http://en.wikipedia.org/wiki/Object-oriented_programming


Is MATLAB OOP slow or am I doing something wrong?

What other programs do the same thing as gprof?

Alternatives to gprof

In Scala, what&#39;s the best way to dynamically instantiate an object and invoke a method using reflection?

I would like to do Scala-equivalent of the following Java code:

    Class class = Class.forName(&quot;Foo&quot;);
    Object foo = class.newInstance();
    Method method = class.getMethod(&quot;hello&quot;, null);
    method.invoke(foo, null);

In the above code, both the class name and the method name are passed in dynamically. The above Java mechanism could probably be used for `Foo` and `hello()`, but the Scala types don&#39;t match one-to-one with that of Java. For example, a class may be declared implicitly for a singleton object. Also Scala method allows all sorts of symbols to be its name. Both are resolved by name mangling. See [Interop Between Java and Scala][1].

Another issue seems to be the matching of parameters by resolving overloads and autoboxing, described in [Reflection from Scala - Heaven and Hell][2].  

  [1]: http://www.codecommit.com/blog/java/interop-between-java-and-scala
  [2]: http://www.familie-kneissl.org/Members/martin/blog/reflection-from-scala-heaven-and-hell

Scala: How do I dynamically instantiate an object and invoke a method using reflection?

Is there any way to get back the mangled name from demangled name in g++.

For example , I have the demangled name `func(char*, int)`, what should I do to get the mangled name i.e `_Z4funcPci` back? 

My question is g++ specific.

Getting mangled name from demangled name

I had an interview recently and one question asked was what is the use of `extern &quot;C&quot;` in C++ code. I replied that it is to use C functions in C++ code as C doesn&#39;t use name-mangling. I was asked why C doesn&#39;t use name-mangling and to be honest I couldn&#39;t answer.

I understand that when the C++ compiler compiles functions, it gives a special name to the function mainly because we can have overloaded functions of the same name in C++ which must be resolved at compile time. In C, the name of the function will stay the same, or maybe with an _ before it.

My query is: what&#39;s wrong with allowing the C++ compiler to mangle C functions also? I would have assumed that it doesn&#39;t matter what names the compiler gives to them. We call functions in the same way in C and C++. 


Content Type	Original Author	Original Content on Stackoverflow
Question	vehomzzz	View Question on Stackoverflow
Solution 1 - C++	Dan Moulding	View Answer on Stackoverflow
Solution 2 - C++	Mike Dunlavey	View Answer on Stackoverflow

How can I see symbols of (C and C++) binary on linux?

C++ Problem Overview

C++ Solutions

Solution 1 - C++

Solution 2 - C++

Java exception not caught

Attaching an event to multiple elements at one go

Attributions