You need:

 - a reference so you can access the exception polymorphically
 - a const to increase performance, and tell the compiler you&#39;re not going to modify the object

The latter is not *as much* important as the former, but the only real reason to drop const would be to signal that you want to do changes to the exception (usually useful only if you want to rethrow it with added context into a higher level).

There is basically no reason at all.

Exception objects live in their own memory space&lt;sup&gt;&amp;dagger;&lt;/sup&gt; so you don&#39;t have to worry about catching exceptions created in temporary expressions.

All you&#39;re doing is promising that you won&#39;t modify the exception object, but since exception objects should have [an immutable interface](reliablecpp.com/blog/2013-08-writing-immutable-data-structures)&lt;sup&gt;&amp;Dagger;&lt;/sup&gt;, there is really nothing practical here.

However, it might make you feel warm and cosy when you read it &amp;mdash; that&#39;s how it is for me!

&lt;sub&gt;&lt;sup&gt;&amp;dagger;&lt;/sup&gt; They have their own, special, thread-local stack.&lt;/sub&gt;  
&lt;sub&gt;&lt;sup&gt;&amp;Dagger;&lt;/sup&gt; **Disclaimer:** Boost.Exception breaks this in order to do funky stuff and add exception details, post-construction. But this is hackery!&lt;/sub&gt;

It tells the compiler that you won&#39;t be calling any function which modify the exception, which may help to optimize the code.  Probably doesn&#39;t make much of a difference, but the cost of doing it is very small too.

are you going to modify the exception? if not, it may as well be const.  same reason you SHOULD use const anywhere else (I say SHOULD because it doesn&#39;t really make that much difference on the surface, might help compilers, and also help coders use your code properly and not do stuff they shouldn&#39;t)

exception handlers, may be platform specific, and may put exceptions in funny places because they aren&#39;t expecting them to change?

Some users are reporting occasional JS errors on my site. The error message says &quot;Expected identifier, string or number&quot; and the line number is 423725915, which is just an arbitrary number and changes for each report when this occurs. 
This mostly happens with IE7/ Mozilla 4.0 browsers.

I scanned my code a bunch of times and ran jslint but it didn&#39;t pick anything up - anyone know of the general type of JS problems that lead to this error message?

Possible cases for Javascript error: &quot;Expected identifier, string or number&quot;

I&#39;m looking for a &quot;top ten&quot; list of reasons why we should be connecting to remote databases via web service instead of directly connecting to the db. This is an internal debate right now and I&#39;m pro-web service but losing the argument. I have a basic grasp of WCF / web services, no one else does. We can do whatever we want moving forward but we need to stick with whatever we choose now.

Here is what I&#39;ve come up with. Any more?

1. WCF web services can, if configured correctly, be more secure.
2. Changes to the DB only need to be made at the service level (config file or recompile service).
3. Once setup and hosted, web services are easier to consume.



Why should a developer use web services instead of direct connections to a db?

I&#39;ve heard and read many times that it is better to catch an exception as reference-to-const rather than as reference. Why is:

    try {
        // stuff
    } catch (const std::exception&amp; e) {
        // stuff
    }

better than:

    try {
        // stuff
    } catch (std::exception&amp; e) {
        // stuff
    }



Why catch an exception as reference-to-const?

I've heard and read many times that it is better to catch an exception as reference-to-const rather than as reference. Why is:
<pre><code class="hljs language-php">try {
 // stuff
} catch (const std::exception&#x26; e) {
 // stuff
}
</code></pre>
better than:
<pre><code class="hljs language-php">try {
 // stuff
} catch (std::exception&#x26; e) {
 // stuff
}
</code></pre>

I want to jump from the middle of a `switch` statement, to the loop statement in the following code:

    while (something = get_something())
    {
        switch (something)
        {
        case A:
        case B:
            break;
        default:
            // get another something and try again
            continue;
        }
        // do something for a handled something
        do_something();
    }

Is this a valid way to use `continue`? Are `continue` statements ignored by `switch` statements? Do C and C++ differ on their behaviour here?

Using continue in a switch statement

Are there any downsides with using `make_shared&lt;T&gt;()` instead of using `shared_ptr&lt;T&gt;(new T)`.

[Boost documentation][1] states 

&gt; There have been repeated requests from
&gt; users for a factory function that
&gt; creates an object of a given type and
&gt; returns a shared_ptr to it. Besides
&gt; convenience and style, such a function
&gt; is also exception safe and
&gt; considerably faster because it can use
&gt; a single allocation for both the
&gt; object and its corresponding control
&gt; block, eliminating a significant
&gt; portion of shared_ptr&#39;s construction
&gt; overhead. This eliminates one of the
&gt; major efficiency complaints about
&gt; shared_ptr.

  [1]: http://www.boost.org/doc/libs/1_41_0/libs/smart_ptr/make_shared.html

Are there any downsides with using make_shared to create a shared_ptr

I am learning C++, but I am confused about abstract class and concrete class. Some real world examples would be appreciated.

What is the difference between a concrete class and an abstract class?

I&#39;m implementing a custom container with an STL-like interface.  I have to provide a regular iterator and a const iterator.  Most of the code for the two versions of the iterators is identical .  How can I avoid this duplication?

For example, my container class is `Foo`, and I&#39;m implementating `FooIterator` and `FooConstIterator`.  Both of the iterators have to provide methods like `operator++()` which are identical.

My question is similar to [How do I remove code duplication between similar const and non-const member functions?][1], but the answer to that one is specific to const and non-const methods, especially accessors.  I don&#39;t see how that might generalize to the iterator problem.

Should I have `FooIterator` derive from `FooConstIterator` and extend it with additional non-const methods?  That either leads to virtual methods or method hiding, which seem inappropriate here.

Perhaps `FooIterator` should contain a `FooConstIterator`.  Although that approach does reduce implementation duplication, it seems to re-introduce a lot of boilerplate method definitions.

Is there clever template technique for generating the two iterators from a single definition?  Or perhaps there&#39;s a way to--shudder--use the preprocessor to stamp out these nearly identical classes.

I&#39;ve tried looking at my local STL implementation to see how it handle this.  There are so many helper classes that I&#39;m having trouble grokking the design, but it looks like the functionality is simply duplicated.

In previous projects, my custom container was built on top of a standard STL container, so I didn&#39;t have to provide my own iterators.  That&#39;s not an option in this case.

  [1]: https://stackoverflow.com/questions/123758/how-do-i-remove-code-duplication-between-similar-const-and-non-const-member-funct

How to avoid code duplication implementing const and non-const iterators?

See title. I have a template. I want to force a particular instance of a template to instantiate. How do I do this?

More specifically, can you force an abstract template class to instantiate?

******

I might elaborate as I have the same question.  In my case I am building a library, some of the template implementations are large and include lots of stuff, but are only generated for a couple of types.  I want to compile them in the library and export all the methods, but not include the header with the code everywhere.

ie:

    template&lt;class T&gt;
    OS_EXPORT_DECL class MyTmpl
    {
        T *item1;
    public:
        inline T *simpleGetT() { return(item1); } /* small inline code in here */ } 
        T *doSomeReallyBigMergeStuff(T *b); // note only declaration here
    };

    // *** implementation source file only seen inside library

    template&lt;class T&gt;
    MyTmpl&lt;T&gt;::doSomeReallyBigMergeStuff(T *b)
    {
        ... a really big method, but don&#39;t want to duplicate it, 
            so it is a template ...
    }

I could of course reference all the methods inside the library which would force them to compile and export but the desire isn&#39;t to add un-needed code to the library like the argument formatting for the items and the code to call them etc.

?????  specifically I am building the library for several versions of MSC and GCC and intel compilers.
  

How do I force a particular instance of a C++ template to instantiate?

I am trying to access HTTP link using `HttpURLConnection` in Android to download a file, but I am getting this warning in `LogCat`:

&gt;WARN/System.err(223): java.net.SocketException: Permission denied (maybe missing INTERNET permission) 

I have added `android.Manifest.permission` to my application but it&#39;s still giving the same exception.

How to add manifest permission to an application?

I have code that is logging `Exception.Message`. However, I read an article which states that it&#39;s better to use `Exception.ToString()`. With the latter, you retain more crucial information about the error.

Is this true, and is it safe to go ahead and replace all code logging `Exception.Message`?

I&#39;m also using an XML based layout for [log4net][1]. Is it possible that `Exception.ToString()` may contain invalid XML characters, which may cause issues?

  [1]: http://logging.apache.org/log4net/

Exception.Message vs Exception.ToString()

Someone please explain the difference between `java.lang.RuntimeException` and `java.lang.Exception`?  How do I decide which one to extend if I create my own exception?

Difference between java.lang.RuntimeException and java.lang.Exception

I&#39;ve recently started programming in Ruby, and I am looking at exception handling.

I was wondering if `ensure` was the Ruby equivalent of `finally` in C#? Should I have:
  
    file = File.open(&quot;myFile.txt&quot;, &quot;w&quot;)
    
    begin
      file &lt;&lt; &quot;#{content} \n&quot;
    rescue
      #handle the error here
    ensure
      file.close unless file.nil?
    end
  

or should I do this?

    #store the file
    file = File.open(&quot;myFile.txt&quot;, &quot;w&quot;)
    
    begin
      file &lt;&lt; &quot;#{content} \n&quot;
      file.close
    rescue
      #handle the error here
    ensure
      file.close unless file.nil?
    end

Does `ensure` get called no matter what, even if an exception isn&#39;t raised?

Begin, Rescue and Ensure in Ruby?

What is the upper level exception that I can catch SQLAlechmy exceptions with ?

    &gt;&gt;&gt; from sqlalchemy import exc
    &gt;&gt;&gt; dir(exc)
    [&#39;ArgumentError&#39;, &#39;CircularDependencyError&#39;, &#39;CompileError&#39;, &#39;ConcurrentModificationError&#39;, &#39;DBAPIError&#39;, &#39;DataError&#39;, &#39;DatabaseError&#39;, &#39;DisconnectionError&#39;, &#39;FlushError&#39;, &#39;IdentifierError&#39;, &#39;IntegrityError&#39;, &#39;InterfaceError&#39;, &#39;InternalError&#39;, &#39;InvalidRequestError&#39;, &#39;NoReferenceError&#39;, &#39;NoReferencedColumnError&#39;, &#39;NoReferencedTableError&#39;, &#39;NoSuchColumnError&#39;, &#39;NoSuchTableError&#39;, &#39;NotSupportedError&#39;, &#39;OperationalError&#39;, &#39;ProgrammingError&#39;, &#39;SADeprecationWarning&#39;, &#39;SAPendingDeprecationWarning&#39;, &#39;SAWarning&#39;, &#39;SQLAlchemyError&#39;, &#39;SQLError&#39;, &#39;TimeoutError&#39;, &#39;UnboundExecutionError&#39;, &#39;UnmappedColumnError&#39;, &#39;__builtins__&#39;, &#39;__doc__&#39;, &#39;__file__&#39;, &#39;__name__&#39;, &#39;__package__&#39;]
    &gt;&gt;&gt; 



catching SQLAlchemy exceptions

Can I mix extern and const, as *extern const*? If yes, does the *const* qualifier impose it&#39;s reign only within the scope it&#39;s declared in or should it exactly match the declaration of the translational unit it&#39;s declared in? I.e. can I declare say `extern const int i;` even when the actual *i* is not a const and vice versa?

Mixing extern and const

Selecting constants without referring to a table is perfectly legal in an SQL statement:

    SELECT 1, 2, 3

The result set that the latter returns is a single row containing the values. I was wondering if there is a way to select multiple rows at once using a constant expression, something kind of:

    SELECT ((1, 2, 3), (4, 5, 6), (7, 8, 9))

I would want something like the above that works and returns a result set with 3 rows and 3 columns.

How to select multiple rows filled with constants?

Is there a way in PHP to include a constant in a string without concatenating?

    define(&#39;MY_CONSTANT&#39;, 42);
    
    echo &quot;This is my constant: MY_CONSTANT&quot;;

Include constant in string without concatenating

Can someone explain the difference between a `static` and `const` variable?

Content Type	Original Author	Original Content on Stackoverflow
Question	cairol	View Question on Stackoverflow
Solution 1 - C++	Kornel Kisielewicz	View Answer on Stackoverflow
Solution 2 - C++	Lightness Races in Orbit	View Answer on Stackoverflow
Solution 3 - C++	Warpin	View Answer on Stackoverflow
Solution 4 - C++	matt	View Answer on Stackoverflow
Solution 5 - C++	Aryabhatta	View Answer on Stackoverflow

Why catch an exception as reference-to-const?

C++ Problem Overview

C++ Solutions

Solution 1 - C++

Solution 2 - C++

Solution 3 - C++

Solution 4 - C++

Solution 5 - C++

Why should a developer use web services instead of direct connections to a db?

Possible cases for Javascript error: "Expected identifier, string or number"

Attributions