What's the easiest way to catch an overflow exception in C++?  For example, when I'm writing something like  int a = 10000, b = 100000; int c = a * b;   or (optionally)  std::cout &lt;&lt; a * b;   I'd like to catch an exception (or notification). How to do so? Maybe there is any native solution for GNU C++, isn't there?
I was writing a program in C++ to find all solutions of ab = c, where a, b and c together use all the digits 0-9 exactly once. The program looped over values of a and b, and it ran a digit-counting routine each time on a, b and ab to check if the digits condition was satisfied.  However, spurious solutions can be generated when ab overflows the integer limit. I ended up checking for this using code like:  unsigned long b, c, c_test; ... c_test=c*b;         // Possible overflow if (c_test/b != c) {/* There has been an overflow*/} else c=c_test;      // No overflow   Is there a better way of testing for overflow? I know that some chips have an internal flag that is set when overflow occurs, but I've never seen it accessed through C or C++.    Beware that signed int overflow is undefined behaviour in C and C++, and thus you have to detect it without actually causing it. For signed int overflow before addition, see .
OpenLayers and OSGB 1936 (CRS 27700) I've been working with loads of shapefiles projected according to OSGB 1936 (CRS 27700). The project CRS is set to EPSG:27700 and "On the fly reprojection" to EPSG:27700 is set (I keep this as a default as I work with OSGB 1936 95% of my time).  I decided to download OSM layers from the OpenLayers plugin. When I load this, the EPSG in the bottom right of the screen goes from EPSG:27700 to EPSG:3857   Question 1: should this be happening anyway as it would suggest that the whole project has been re-projected to EPSG:3857?   As soon as the OSM layer is loaded it's way out of alignment but a quick pan seems to bring it altogether quiet nicely.   What I have noted is that (Question 2), if I try to re-specify the CRS to 27700, then the shapefiles "move" by a few tens of meters with respect to the OSM. Does this suggest that QGIS is doing a second re-projection (from what to what?)?   Also (Question 3), does it mean that if I import another shapefile that would be originally a dataset digitised with EPSG:27700 it would be re-projected to EPSG:3857 because the CRS in the bottom right of the screen was set to EPSG:3857 after the OSM import. This is all a bit confusing and logic would suggest that the import of a non-ESPG:27700 (project default CRS) should not go and change the EPSG setting in the bottom right of the screen. Anita Graser's book says on page 34 "Your project CRS will automatically be changed to Pseudo Mercator when you load a background map using the OpenLayers plugin option".   Does that mean there is no way of keeping ESPG:27700 active in the project when importing basemaps from OpenLayers? If so, what alternatives are there?  What I am trying to bottom out is to understand the correct way of importing basemaps (usually Google, Bing or OSM through the OpenLayers plugin) into my projects (always EPSG:27700) without losing alignment and getting layers to correctly re-project. I'm trying to support greater use of QGIS in my company but don't want to lose credibility by promoting the use of a tool that is misaligning datasets. Don't get me wrong. QGIS is a great tool and I am very fond of it but importing layers with different CRS's is quite common these days and getting this right from the start is half the job done.  I did quite an extensive Google search before posting and didn't come up with a recent, clear cut answer to my questions above. There is a bit of content out there on problems with older versions of QGIS, PROJ4, etc. but nothing recent for QGIS 2.0 so worth an update. Generating list of manually installed packages and querying individual packages I'd like to get a list of packages installed manually by apt or aptitude and be able to find out whether a foobar package was installed manually or automatically. Is there any neat way of doing that from the command line? Why could the pictures and paintings in Hogwarts talk and the photos of Harry's parents couldn't? Why am I allowed to turn my focusing ring beyond infinity? Why $9$ & $11$ are special in divisibility tests using decimal digit sums? (casting out nines & elevens) Requesting raw data from previously published research How to diagnose slow booting or logon in Windows? When I start my PC, it boots into Windows (Windows 7 32-bit) quite happily, I login and the main Windows screen appears. At that point, however, the system is extremely unresponsive for up to 5 minutes - if I click on Firefox to start it, nothing appears to happen for a long time, etc, etc. The mouse and Windows UI is responsive, but programs take forever to start, webpages seem to hang (or at least load extremely slowly) and so on.  I imagine that the issue is with one or more programs that run on startup, but I don't know quite how to identify which one it might be. The event log shows nothing of any obvious interest. I can't see any high CPU activity in task manager or Process Explorer, and I can't hear any high disk activity.  I'd rather understand what's happening and then work out how to address it, than have to go for a blind "switch things off and see what helps" approach, but maybe that's being optimistic :-)  I suspect disk bottlenecks or network, but I don't know how I could set something up to diagnose this (and in particular, given that I can't get programs to start in a timely manner, I'd prefer something that automatically starts and logs data for later analysis than something like Process Explorer, which always leaves me worrying that by the time it started the problem had gone away :-)  I guess my ideal would be 2 things:   Something that gave me an overall "what are the current key bottlenecks in this system" summary (ideally, which could be set to run in the background and collect data for later analysis). Some means of starting a program (say, Firefox) and have it record what was going on in terms of waits and delays in the system.   Unfortunately, I've never really found anything like either of these.  I'm not a professional systems admin - my background is database admin - so if there are "obvious" tools to look at or try, then I'd be grateful to know of them (particularly if the information they give is easy for an amateur to analyze) :-) How to avoid noisy renders in Cycles? I know that this question is a bit old or maybe overdone, but I'm running the latest edition of Blender and when I use the Cycles engine I get really fuzzy results and I can't find a simple, non-compromising solution to the quality.  I don't know exactly what I'm doing wrong here, but I'm sure others share my frustration.  Leaving everything in default settings, I started a new project and switched to the Cycles render.  I duplicated the cube and set colors for two Diffuse BSDF shaders, then went ahead and made walls and a floor all sharing the same diffuse shader.  I made two windows to emit blue light.  The screenshot has gaps between the walls because of the setup:  I'm aware that it's considered very incomplete and many have come to terms with some amount of noise, but is this normal?  Furthermore, with default settings or not, I can't change the amount of noise produced.  Supposedly, using "progressively refine" in the rendering tab should make it refine itself indefinitely, however Cycles only counts to 10 refines and then stops, creating a render which is a pixel-perfect match of the ordinary rendering method when it's completed.  I understand that there are tricks that can be used to reduce noise, but at the cost of extra processing time and usually small quality conflicts, like blurring.  My question essentially boils down to is this Cycles' current limit? Do photons have acceleration? Determining whether two $k$-chromatic graphs are isomorphic (respecting vertex coloration) How to get rid of the smell from the fridge? check if numbers from command line are powers of 2 How does a USB 2.0 Wall Charger negotiate current output? I'm trying to use a mobile phone charger for my projects, and want a high current output. I have read , however my measurements show something else.  is a link to the Battery Charging Specification Rev. 1.2.  1.4.7 Dedicated Charging Port A Dedicated Charging Port (DCP) is a downstream port on a device that outputs power through a USB connector, but is not capable of enumerating a downstream device. A DCP shall source \$I_{DCP}\$ at an average voltage of \$V_{CHG}\$. A DCP shall short the D+ line to the D- line.   I verified on three different chargers, and all read \$R_{DCP\_DAT}\$ as ~1.5 Ohms. Now, if there is a short between the D+ and D-, there is no detection on the charging port side, and the charger should always output \$I_{DCP}\$ {0.5 - 5.0A max} on the VBUS line - is this correct? I tested the current output of three chargers, but they are all completely different. Charger 1 - Nokia Rated current output: 1.3A Measured current output: 1.34A Charger 2 - Asus Rated current output: 2.0A Measured current output: 0.7A - 1.1A (unstable) Charger 3 - HTC Rated current output: 1A Measurent current output: 0.1A If all these dedicated charging ports have no current negotiation, how come only one charger is showing it's rated output? N.B All three chargers can charge a mobile phone in a reasonable amount of time. How can we unlock an iPhone backup file if we don't know the password? persist port routing from 80 to 8080 I use amazon EC2 instance which works via ubuntu. By default according security restrictions I can't bin my application to port 80, so I just bind it port 8080 and then set routing redirect from port 80 to 8080 via the following command:  iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to 8080   But I found that when I reboot the server this settings no longer active untill I invoke this command again.  So my question is how to enable port's redirect work even if system was rebooted? A two column loop with one lead post I got a loop from internet (I forgot the site) for two column post view. It has a nice CSS for it too. But skipping that for the question now.  &lt;?php $counter = 1; ?&gt;                  &lt;?php query_posts( 'cat=3&amp;showposts=6' ); //Find whether the catID is 3 ?&gt;             &lt;?php while ( have_posts() ) : the_post() ?&gt;                   &lt;?php /* Two Column Support get class */ ?&gt;              &lt;?php $class = ( $counter % 2  ? ' one' : '' ) ?&gt;                  &lt;?php /* Two Column output open the div class */ ?&gt;              &lt;div class="column&lt;?php echo $class;// echo $first; ?&gt;"&gt;              &lt;?php news_format(); ?&gt;             &lt;/div&gt; &lt;!-- End Two Column Support close div class --&gt; &lt;?php $counter++; //Update counter ?&gt;   It printed my posts into 2 columns like:  ========= | 1 | 2 | --------- | 3 | 4 | --------- | 5 | 6 | =========  It's fine. But I want to print it like this:  ========= |   1   | --------- | 2 | 3 | --------- | 4 | 5 | --------- | 6 | 7 | =========  What the modification I need to do? I can't pass any custom limit into the WordPress' custom loop &lt;?php while ( have_posts() ) : the_post() ?&gt;. It's for a custom theme. I did it, but the problem is, it's showing like:  ========= |   1   | --------- | 1 | 2 | --------- | 3 | 4 | --------- | 5 | 6 | =========   is my whole bunch of code. What's wrong with this derivation that $i\hbar = 0$? How can the following inequation be proven?  $$a^2 + b^2 + c^2 \ge ab + bc + ca$$ The square roots of different primes are linearly independent over the field of rationals Local file access with JavaScript Is there local file manipulation that's been done with JavaScript? I'm looking for a solution that can be accomplished with no install footprint like requiring .  Specifically, I'd like to read the contents from a file and write those contents to another file. At this point I'm not worried about gaining permissions and am just assuming I already have full permissions to these files.