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• Understanding CLR 2.0 Memory Model

  - by Eloff

  Joe Duffy, gives 6 rules that describe the CLR 2.0+ memory model (it's actual implementation, not any ECMA standard) I'm writing down my attempt at figuring this out, mostly as a way of rubber ducking, but if I make a mistake in my logic, at least someone here will be able to catch it before it causes me grief. Rule 1: Data dependence among loads and stores is never violated. Rule 2: All stores have release semantics, i.e. no load or store may move after one. Rule 3: All volatile loads are acquire, i.e. no load or store may move before one. Rule 4: No loads and stores may ever cross a full-barrier (e.g. Thread.MemoryBarrier, lock acquire, Interlocked.Exchange, Interlocked.CompareExchange, etc.). Rule 5: Loads and stores to the heap may never be introduced. Rule 6: Loads and stores may only be deleted when coalescing adjacent loads and stores from/to the same location. I'm attempting to understand these rules. x = y y = 0 // Cannot move before the previous line according to Rule 1. x = y z = 0 // equates to this sequence of loads and stores before possible re-ordering load y store x load 0 store z Looking at this, it appears that the load 0 can be moved up to before load y, but the stores may not be re-ordered at all. Therefore, if a thread sees z == 0, then it also will see x == y. If y was volatile, then load 0 could not move before load y, otherwise it may. Volatile stores don't seem to have any special properties, no stores can be re-ordered with respect to each other (which is a very strong guarantee!) Full barriers are like a line in the sand which loads and stores can not be moved over. No idea what rule 5 means. I guess rule 6 means if you do: x = y x = z Then it is possible for the CLR to delete both the load to y and the first store to x. x = y z = y // equates to this sequence of loads and stores before possible re-ordering load y store x load y store z // could be re-ordered like this load y load y store x store z // rule 6 applied means this is possible? load y store x // but don't pop y from stack (or first duplicate item on top of stack) store z What if y was volatile? I don't see anything in the rules that prohibits the above optimization from being carried out. This does not violate double-checked locking, because the lock() between the two identical conditions prevents the loads from being moved into adjacent positions, and according to rule 6, that's the only time they can be eliminated. So I think I understand all but rule 5, here. Anyone want to enlighten me (or correct me or add something to any of the above?)

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• Android problem: BufferedReader wont read whole stream into a string

  - by Levara

  Hi all! I'm making an android program that retrieves content of a webpage using HttpURLConnection. I'm new to both Java and Android. Problem is: Reader reads whole page source, but in the last while iteration it doesn't append to stringBuffer that last part. Using debbuger I have determined that, in the last loop iteration, string buff is created, but stringBuffer just doesnt append it. I need to parse retrieved content. Is there any better way to handle the content for parsing than using strings. I've read on numerous other sites that string size in Java is limited only by available heap size. Anyone know what could be the problem. Btw feel free to suggest any improvements to the code. Thanks! URL u; try { u = new URL("http://feeds.timesonline.co.uk/c/32313/f/440134/index.rss"); HttpURLConnection c = (HttpURLConnection) u.openConnection(); c.setRequestProperty("User-agent","Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322; InfoPath.1; .NET CLR 2.0.50727)"); c.setRequestMethod("GET"); c.setDoOutput(true); c.setReadTimeout(3000); c.connect(); StringBuffer stringBuffer = new StringBuffer(""); InputStream in = c.getInputStream(); InputStreamReader inp = new InputStreamReader(in); BufferedReader reader = new BufferedReader(inp); char[] buffer = new char[3072]; int len1 = 0; while ( (len1 = reader.read(buffer)) != -1 ) { String buff = new String(buffer,0,len1); stringBuffer.append(buff); } String stranica = new String(stringBuffer); c.disconnect(); reader.close(); inp.close(); in.close();

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• PHP Processes reaching limit along with FastCGI timeouts

  - by Constant M

  I have a problem similar to http://stackoverflow.com/questions/1168384/how-to-troubleshoot-php-processes, but with a twist. We have a couple of managed servers that recently migrated to FastCGI. Since then we've been having problems. We have a content management system at a central place that we manage all our sites with. All the sites run on the same managed server. So basically its one PHP script that generates pages on the same server. The catch comes in where it works perfectly on some, and gives FCGI timeout errors on others. At the same time our support is saying that the PHP processes heap up to their limit and then causes Apache to stop working. I'm convinced this is a fault on their side, but would like to get my side clean too. Anyway have any suggestions where I can start looking for what's going wrong? I know it's a really broad question, but any help or pointers would be great. Thanks Just to add to that, here's a PS printout from support: happyh 13853 21556 0 01:04 ? 00:00:00 /usr/bin/php5-cgi happyh 13869 13853 0 01:04 ? 00:00:00 /usr/bin/php5-cgi mamedc 13914 21556 0 05:14 ? 00:00:00 /usr/bin/php5-cgi wealthf 13947 21556 0 01:21 ? 00:00:00 /usr/bin/php5-cgi wealthf 13961 13947 0 01:21 ? 00:00:00 /usr/bin/php5-cgi mamedc 14032 13914 0 05:14 ? 00:00:00 /usr/bin/php5-cgi lookgrt 14157 21556 0 04:47 ? 00:00:00 /usr/bin/php5-cgi lookgrt 14178 14157 0 04:47 ? 00:00:00 /usr/bin/php5-cgi wolfie 14262 21556 0 01:08 ? 00:00:00 /usr/bin/php5-cgi wolfie 14276 14262 0 01:08 ? 00:00:00 /usr/bin/php5-cgi yaukrl 14352 21556 0 01:21 ? 00:00:00 /usr/bin/php5-cgi yaukrl 14361 14352 0 01:21 ? 00:00:00 /usr/bin/php5-cgi itpays2 14538 21556 0 01:33 ? 00:00:00 /usr/bin/php5-cgi itpays2 14547 14538 0 01:33 ? 00:00:00 /usr/bin/php5-cgi brichmbx 14732 21556 0 04:47 ? 00:00:00 /usr/bin/php5-cgi brichmbx 14803 14732 0 04:47 ? 00:00:00 /usr/bin/php5-cgi greatl 14969 21556 0 01:00 ? 00:00:00 /usr/bin/php5-cgi

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• C++ Program Always Crashes While doing a std::string assign

  - by bbazso

  I have been trying to debug a crash in my application that crashes (i.e. asserts a * glibc detected free(): invalid pointer: 0x000000000070f0c0 **) while I'm trying to do a simple assign to a string. Note that I'm compiling on a linux system with gcc 4.2.4 with an optimization level set to -O2. With -O0 the application no longer crashes. E.g. std::string abc; abc = "testString"; but if I changed the code as follows it no longer crashes std::string abc("testString"); So again I scratched my head! But the interesting pattern was that the crash moved later on in the application, AGAIN at another string. I found it weird that the application was continuously crashing on a string assign. A typical crash backtrace would look as follows: #0 0x00007f2c2663bfb5 in raise () from /lib64/libc.so.6 (gdb) bt #0 0x00007f2c2663bfb5 in raise () from /lib64/libc.so.6 #1 0x00007f2c2663dbc3 in abort () from /lib64/libc.so.6 #2 0x00000000004d8cb7 in people_streamingserver_sighandler (signum=6) at src/peoplestreamingserver.cpp:487 #3 <signal handler called> #4 0x00007f2c2663bfb5 in raise () from /lib64/libc.so.6 #5 0x00007f2c2663dbc3 in abort () from /lib64/libc.so.6 #6 0x00007f2c26680ce0 in ?? () from /lib64/libc.so.6 #7 0x00007f2c270ca7a0 in std::string::assign (this=0x7f2c21bc8d20, __str=<value optimized out>) at /home/bbazso/ThirdParty/sources/gcc-4.2.4/x86_64-pc-linux-gnu/libstdc++-v3/include/bits/basic_string.h:238 #8 0x00007f2c21bd874a in PEOPLESProtocol::GetStreamName (this=<value optimized out>, pRawPath=0x2342fd8 "rtmp://127.0.0.1/mp4:pop.mp4", lStreamName=@0x7f2c21bc8d20) at /opt/trx-HEAD/gcc/4.2.4/lib/gcc/x86_64-pc-linux-gnu/4.2.4/../../../../include/c++/4.2.4/bits/basic_string.h:491 #9 0x00007f2c21bd9daa in PEOPLESProtocol::SignalProtocolCreated (pProtocol=0x233a4e0, customParameters=@0x7f2c21bc8de0) at peoplestreamer/src/peoplesprotocol.cpp:240 This was really weird behavior and so I started to poke around further in my application to see if there was some sort of memory corruption (either heap or stack) error that could be occurring that could be causing this weird behavior. I even checked for ptr corruptions and came up empty handed. In addition to visual inspection of the code I also tried the following tools: Valgrind using both memcheck and exp-ptrcheck electric fence libsafe I compiled with -fstack-protector-all in gcc I tried MALLOC_CHECK_ set to 2 I ran my code through lint checks as well as cppcheck (to check for mistakes) And I stepped through the code using gdb So I tried a lot of stuff and still came up empty handed. So I was wondering if it could be something like a linker issue or a library issue of some sort that could be causing this problem. Are there any know issues with the std::string that make is susceptible to crashing in -O2 or maybe it has nothing to do with the optimization level? But the only pattern that I can see thus far in my problem is that it always seems to crash on a string and so I was wondering if anyone knew of any issues that my be causing this type of behavior. Thanks a lot!

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• How do I prove I should put a table of values in source code instead of a database table?

  - by FastAl

  <tldr>looking for a reference to a book or other undeniably authoritative source that gives reasons when you should choose a database vs. when you should choose other storage methods. I have provided an un-authoritative list of reasons about 2/3 of the way down this post.</tldr> I have a situation at my company where a database is being used where it would be better to use another solution (in this case, an auto-generated piece of source code that contains a static lookup table, searched by binary sort). Normally, a database would be an OK solution even though the problem does not require a database, e.g, none of the elements of ACID are needed, as it is read-only data, updated about every 3-5 years (also requiring other sourcecode changes), and fits in memory, and can be keyed into via binary search (a tad faster than db, but speed is not an issue). The problem is that this code runs on our enterprise server, but is shared with several PC platforms (some disconnected, some use a central DB, etc.), and parts of it are managed by multiple programming units, parts by the DBAs, parts even by mathematicians in another department, etc. These hit their own platform’s version of their databases (containing their own copy of the static data). What happens is that every implementation, every little change, something different goes wrong. There are many other issues as well. I can’t even use a flatfile, because one mode of running on our enterprise server does not have permission to read files (only databases, and of course, its own literal storage, e.g., in-source table). Of course, other parts of the system use databases in proper, less obscure manners; there is no problem with those parts. So why don’t we just change it? I don’t have administrative ability to force a change. But I’m affected because sometimes I have to help fix the problems, but mostly because it causes outages and tons of extra IT time by other programmers and d*mmit that makes me mad! The reason neither management, nor the designers of the system, can see the problem is that they propose a solution that won’t work: increase communication; implement more safeguards and standards; etc. But every time, in a different part of the already-pared-down but still multi-step processes, a few different diligent, hard-working, top performing IT personnel make a unique subtle error that causes it to fail, sometimes after the last round of testing! And in general these are not single-person failures, but understandable miscommunications. And communication at our company is actually better than most. People just don't think that's the case because they haven't dug into the matter. However, I have it on very good word from somebody with extensive formal study of sociology and psychology that the relatively small amount of less-than-proper database usage in this gigantic cross-platform multi-source, multi-language project is bureaucratically un-maintainable. Impossible. No chance. At least with Human Beings in the loop, and it can’t be automated. In addition, the management and developers who could change this, though intelligent and capable, don’t understand the rigidity of this ‘how humans are’ issue, and are not convincible on the matter. The reason putting the static data in sourcecode will solve the problem is, although the solution is less sexy than a database, it would function with no technical drawbacks; and since the sharing of sourcecode already works very well, you basically erase any database-related effort from this section of the project, along with all the drawbacks of it that are causing problems. OK, that’s the background, for the curious. I won’t be able to convince management that this is an unfixable sociological problem, and that the real solution is coding around these limits of human nature, just as you would code around a bug in a 3rd party component that you can’t change. So what I have to do is exploit the unsuitableness of the database solution, and not do it using logic, but rather authority. I am aware of many reasons, and posts on this site giving reasons for one over the other; I’m not looking for lists of reasons like these (although you can add a comment if I've miss a doozy): WHY USE A DATABASE? instead of flatfile/other DB vs. file: if you need... Random Read / Transparent search optimization Advanced / varied / customizable Searching and sorting capabilities Transaction/rollback Locks, semaphores Concurrency control / Shared users Security 1-many/m-m is easier Easy modification Scalability Load Balancing Random updates / inserts / deletes Advanced query Administrative control of design, etc. SQL / learning curve Debugging / Logging Centralized / Live Backup capabilities Cached queries / dvlp & cache execution plans Interleaved update/read Referential integrity, avoid redundant/missing/corrupt/out-of-sync data Reporting (from on olap or oltp db) / turnkey generation tools [Disadvantages:] Important to get right the first time - professional design - but only b/c it's meant to last s/w & h/w cost Usu. over a network, speed issue (best vs. best design vs. local=even then a separate process req's marshalling/netwk layers/inter-p comm) indicies and query processing can stand in the way of simple processing (vs. flatfile) WHY USE FLATFILE: If you only need... Sequential Row processing only Limited usage append only (no reading, no master key/update) Only Update the record you're reading (fixed length recs only) Too big to fit into memory If Local disk / read-ahead network connection Portability / small system Email / cut & Paste / store as document by novice - simple format Low design learning curve but high cost later WHY USE IN-MEMORY/TABLE (tables, arrays, etc.): if you need... Processing a single db/ff record that was imported Known size of data Static data if hardcoding the table Narrow, unchanging use (e.g., one program or proc) -includes a class that will be shared, but encapsulates its data manipulation Extreme speed needed / high transaction frequency Random access - but search is dependent on implementation Following are some other posts about the topic: http://stackoverflow.com/questions/1499239/database-vs-flat-text-file-what-are-some-technical-reasons-for-choosing-one-over http://stackoverflow.com/questions/332825/are-flat-file-databases-any-good http://stackoverflow.com/questions/2356851/database-vs-flat-files http://stackoverflow.com/questions/514455/databases-vs-plain-text/514530 What I’d like to know is if anybody could recommend a hard, authoritative source containing these reasons. I’m looking for a paper book I can buy, or a reputable website with whitepapers about the issue (e.g., Microsoft, IBM), not counting the user-generated content on those sites. This will have a greater change to elicit a change that I’m looking for: less wasted programmer time, and more reliable programs. Thanks very much for your help. You win a prize for reading such a large post!

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• How to optimize this SQL query for a rectangular region?

  - by Andrew B.

  I'm trying to optimize the following query, but it's not clear to me what index or indexes would be best. I'm storing tiles in a two-dimensional plane and querying for rectangular regions of that plane. The table has, for the purposes of this question, the following columns: id: a primary key integer world_id: an integer foreign key which acts as a namespace for a subset of tiles tileY: the Y-coordinate integer tileX: the X-coordinate integer value: the contents of this tile, a varchar if it matters. I have the following indexes: "ywot_tile_pkey" PRIMARY KEY, btree (id) "ywot_tile_world_id_key" UNIQUE, btree (world_id, "tileY", "tileX") "ywot_tile_world_id" btree (world_id) And this is the query I'm trying to optimize: ywot=> EXPLAIN ANALYZE SELECT * FROM "ywot_tile" WHERE ("world_id" = 27685 AND "tileY" <= 6 AND "tileX" <= 9 AND "tileX" >= -2 AND "tileY" >= -1 ); QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------- Bitmap Heap Scan on ywot_tile (cost=11384.13..149421.27 rows=65989 width=168) (actual time=79.646..80.075 rows=96 loops=1) Recheck Cond: ((world_id = 27685) AND ("tileY" <= 6) AND ("tileY" >= (-1)) AND ("tileX" <= 9) AND ("tileX" >= (-2))) -> Bitmap Index Scan on ywot_tile_world_id_key (cost=0.00..11367.63 rows=65989 width=0) (actual time=79.615..79.615 rows=125 loops=1) Index Cond: ((world_id = 27685) AND ("tileY" <= 6) AND ("tileY" >= (-1)) AND ("tileX" <= 9) AND ("tileX" >= (-2))) Total runtime: 80.194 ms So the world is fixed, and we are querying for a rectangular region of tiles. Some more information that might be relevant: All the tiles for a queried region may or may not be present The height and width of a queried rectangle are typically about 10x10-20x20 For any given (world, X) or (world, Y) pair, there may be an unbounded number of matching tiles, but the worst case is currently around 10,000, and typically there are far fewer. New tiles are created far less frequently than existing ones are updated (changing the 'value'), and that itself is far less frequent that just reading as in the query above. The only thing I can think of would be to index on (world, X) and (world, Y). My guess is that the database would be able to take those two sets and intersect them. The problem is that there is a potentially unbounded number of matches for either for either of those. Is there some other kind of index that would be more appropriate?

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• Autocomplete server-side implementation

  - by toluju

  What is a fast and efficient way to implement the server-side component for an autocomplete feature in an html input box? I am writing a service to autocomplete user queries in our web interface's main search box, and the completions are displayed in an ajax-powered dropdown. The data we are running queries against is simply a large table of concepts our system knows about, which matches roughly with the set of wikipedia page titles. For this service obviously speed is of utmost importance, as responsiveness of the web page is important to the user experience. The current implementation simply loads all concepts into memory in a sorted set, and performs a simple log(n) lookup on a user keystroke. The tailset is then used to provide additional matches beyond the closest match. The problem with this solution is that it does not scale. It currently is running up against the VM heap space limit (I've set -Xmx2g, which is about the most we can push on our 32 bit machines), and this prevents us from expanding our concept table or adding more functionality. Switching to 64-bit VMs on machines with more memory isn't an immediate option. I've been hesitant to start working on a disk-based solution as I am concerned that disk seek time will kill performance. Are there possible solutions that will let me scale better, either entirely in memory or with some fast disk-backed implementations? Edits: @Gandalf: For our use case it is important the the autocompletion is comprehensive and isn't just extra help for the user. As for what we are completing, it is a list of concept-type pairs. For example, possible entries are [("Microsoft", "Software Company"), ("Jeff Atwood", "Programmer"), ("StackOverflow.com", "Website")]. We are using Lucene for the full search once a user selects an item from the autocomplete list, but I am not yet sure Lucene would work well for the autocomplete itself. @Glen: No databases are being used here. When I'm talking about a table I just mean the structured representation of my data. @Jason Day: My original implementation to this problem was to use a Trie, but the memory bloat with that was actually worse than the sorted set due to needing a large number of object references. I'll read on the ternary search trees to see if it could be of use.

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• How can I pass managed objects from one AppDomain to another?

  - by Dennis P

  I have two assemblies that I'm trying to link together. One is a sort of background process that's built with WinForms and will be designed to run as a Windows Service. I have a second project that will act as a UI for the background process whenever a user launches it. I've never tried attempting something like this with managed code before, so I've started trying to use windows messages to communicate between the two processes. I'm struggling when it comes to passing more than just IntPtrs back and forth, however. Here's the code from a control in my UI project that registers itself with the background process: public void Init() { IntPtr hwnd = IntPtr.Zero; Process[] ps = Process.GetProcessesByName("BGServiceApp"); Process mainProcess = null; if(ps == null || ps.GetLength(0) == 0) { mainProcess = LaunchApp(); } else { mainProcess = ps[0]; } SendMessage(mainProcess.MainWindowHandle, INIT_CONNECTION, this.Handle, IntPtr.Zero); } protected override void WndProc(ref Message m) { if(m.Msg == INIT_CONFIRMED && InitComplete != null) { string message = Marshal.PtrToStringAuto(m.WParam); Marshal.FreeHGlobal(m.WParam); InitComplete(message, EventArgs.Empty); } base.WndProc(ref m); } This is the code from the background process that's supposed to receive a request from the UI process to register for status updates and send a confirmation message. protected override void WndProc(ref Message m) { if(m.Msg == INIT_CONNECTION) { RegisterUIDispatcher(m.WParam); Respond(m.WParam); } if(m.Msg == UNINIT_CONNECTION) { UnregisterUIDispatcher(m.WParam); if(m_RegisteredDispatchers.Count == 0) { this.Close(); } } base.WndProc(ref m); } private void Respond(IntPtr caller) { string test = "Registration confirmed!"; IntPtr ptr = Marshal.StringToHGlobalAuto(test); SendMessage(caller, INIT_CONFIRMED, ptr, IntPtr.Zero); } } The UI process receives the INIT_CONFIRMED message from my background process, but when I try to marshal the IntPtr back into a string, I get an empty string. Is the area of heap I'm using out of scope to the other process or am I missing some security attribute maybe? Is there a better and cleaner way to go about something like this using an event driven model?

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• Parallel.For maintain input list order on output list

  - by romeozor

  I'd like some input on keeping the order of a list during heavy-duty operations that I decided to try to do in a parallel manner to see if it boosts performance. (It did!) I came up with a solution, but since this was my first attempt at anything parallel, I'd need someone to slap my hands if I did something very stupid. There's a query that returns a list of card owners, sorted by name, then by date of birth. This needs to be rendered in a table on a web page (ASP.Net WebForms). The original coder decided he would construct the table cell-by-cell (TableCell), add them to rows (TableRow), then each row to the table. So no GridView, allegedly its performance is bad, but the performance was very poor regardless :). The database query returns in no time, the most time is spent on looping through the results and adding table cells etc. I made the following method to maintain the original order of the list: private TableRow[] ComposeRows(List<CardHolder> queryResult) { int queryElementsCount = queryResult.Count(); // array with the query's size var rowArray = new TableRow[queryElementsCount]; Parallel.For(0, queryElementsCount, i => { var row = new TableRow(); var cell = new TableCell(); // various operations, including simple ones such as: cell.Text = queryResult[i].Name; row.Cells.Add(cell); // here I'm adding the current item to it's original index // to maintain order in the output list rowArray[i] = row; }); return rowArray; } So as you can see, because I'm returning a very different type of data (List<CardHolder> -> TableRow[]), I can't just simply omit the ordering from the original query to do it after the operations. Also, I also thought it would be a good idea to Dispose() the objects at the end of each loop, because the query can return a huge list and letting cell and row objects pile up in the heap could impact performance.(?) How badly did I do? Does anyone have a better solution in case mine is flawed?

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• Java Runtime.freeMemory() returning bizarre results when adding more objects

  - by Sotirios Delimanolis

  For whatever reason, I wanted to see how many objects I could create and populate a LinkedList with. I used Runtime.getRuntime().freeMemory() to get the approximation of free memory in my JVM. I wrote this: public static void main(String[] arg) { Scanner kb = new Scanner(System.in); List<Long> mem = new LinkedList<Long>(); while (true) { System.out.println("Max memory: " + Runtime.getRuntime().maxMemory() + ". Available memory: " + Runtime.getRuntime().freeMemory() + " bytes. Press enter to use more."); String s = kb.nextLine(); if (s.equals("m")) for (int i = 0; i < 1000000; i++) { mem.add(new Long((new Random()).nextLong())); } } } If I write in m, the app adds a million Long objects to the list. You would think the more objects (to which we have references, so can't be gc'ed), the less free memory. Running the code: Max memory: 1897725952. Available memory: 127257696 bytes. m Max memory: 1897725952. Available memory: 108426520 bytes. m Max memory: 1897725952. Available memory: 139873296 bytes. m Max memory: 1897725952. Available memory: 210632232 bytes. m Max memory: 1897725952. Available memory: 137268792 bytes. m Max memory: 1897725952. Available memory: 239504784 bytes. m Max memory: 1897725952. Available memory: 169507792 bytes. m Max memory: 1897725952. Available memory: 259686128 bytes. m Max memory: 1897725952. Available memory: 189293488 bytes. m Max memory: 1897725952. Available memory: 387686544 bytes. The available memory fluctuates. How does this happen? Is the GC cleaning up other things (what other things are there on the heap to really clean up?), is the freeMemory() method returning an approximation that's way off? Am I missing something or am I crazy?

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• Who calls the Destructor of the class when operator delete is used in multiple inheritance.

  - by dicaprio-leonard

  This question may sound too silly, however , I don't find concrete answer any where else. With little knowledge on how late binding works and virtual keyword used in inheritance. As in the code sample, when in case of inheritance where a base class pointer pointing to a derived class object created on heap and delete operator is used to deallocate the memory , the destructor of the of the derived and base will be called in order only when the base destructor is declared virtual function. Now my question is : 1) When the destructor of base is not virtual, why the problem of not calling derived dtor occur only when in case of using "delete" operator , why not in the case given below: derived drvd; base *bPtr; bPtr = &drvd; //DTOR called in proper order when goes out of scope. 2) When "delete" operator is used, who is reponsible to call the destructor of the class? The operator delete will have an implementation to call the DTOR ? or complier writes some extra stuff ? If the operator has the implementation then how does it looks like , [I need sample code how this would have been implemented]. 3) If virtual keyword is used in this example, how does operator delete now know which DTOR to call? Fundamentaly i want to know who calls the dtor of the class when delete is used. Sample Code class base { public: base() { cout<<"Base CTOR called"<<endl; } virtual ~base() { cout<<"Base DTOR called"<<endl; } }; class derived:public base { public: derived() { cout<<"Derived CTOR called"<<endl; } ~derived() { cout<<"Derived DTOR called"<<endl; } }; I'm not sure if this is a duplicate, I couldn't find in search. int main() { base *bPtr = new derived(); delete bPtr;// only when you explicitly try to delete an object return 0; }

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• Good style for handling constructor failure of critical object

  - by mtlphil

  I'm trying to decide between two ways of instantiating an object & handling any constructor exceptions for an object that is critical to my program, i.e. if construction fails the program can't continue. I have a class SimpleMIDIOut that wraps basic Win32 MIDI functions. It will open a MIDI device in the constructor and close it in the destructor. It will throw an exception inherited from std::exception in the constructor if the MIDI device cannot be opened. Which of the following ways of catching constructor exceptions for this object would be more in line with C++ best practices Method 1 - Stack allocated object, only in scope inside try block #include <iostream> #include "simplemidiout.h" int main() { try { SimpleMIDIOut myOut; //constructor will throw if MIDI device cannot be opened myOut.PlayNote(60,100); //..... //myOut goes out of scope outside this block //so basically the whole program has to be inside //this block. //On the plus side, it's on the stack so //destructor that handles object cleanup //is called automatically, more inline with RAII idiom? } catch(const std::exception& e) { std::cout << e.what() << std::endl; std::cin.ignore(); return 1; } std::cin.ignore(); return 0; } Method 2 - Pointer to object, heap allocated, nicer structured code? #include <iostream> #include "simplemidiout.h" int main() { SimpleMIDIOut *myOut; try { myOut = new SimpleMIDIOut(); } catch(const std::exception& e) { std::cout << e.what() << std::endl; delete myOut; return 1; } myOut->PlayNote(60,100); std::cin.ignore(); delete myOut; return 0; } I like the look of the code in Method 2 better, don't have to jam my whole program into a try block, but Method 1 creates the object on the stack so C++ manages the object's life time, which is more in tune with RAII philosophy isn't it? I'm still a novice at this so any feedback on the above is much appreciated. If there's an even better way to check for/handle constructor failure in a siatuation like this please let me know.

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• Memory Leak with Swing Drag and Drop

  - by tom

  I have a JFrame that accepts top-level drops of files. However after a drop has occurred, references to the frame are held indefinitely inside some Swing internal classes. I believe that disposing of the frame should release all of its resources, so what am I doing wrong? Example import java.awt.datatransfer.DataFlavor; import java.io.File; import java.util.List; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.TransferHandler; public class DnDLeakTester extends JFrame { public static void main(String[] args) { new DnDLeakTester(); //Prevent main from returning or the jvm will exit while (true) { try { Thread.sleep(10000); } catch (InterruptedException e) { } } } public DnDLeakTester() { super("I'm leaky"); add(new JLabel("Drop stuff here")); setTransferHandler(new TransferHandler() { @Override public boolean canImport(final TransferSupport support) { return (support.isDrop() && support .isDataFlavorSupported(DataFlavor.javaFileListFlavor)); } @Override public boolean importData(final TransferSupport support) { if (!canImport(support)) { return false; } try { final List<File> files = (List<File>) support.getTransferable().getTransferData(DataFlavor.javaFileListFlavor); for (final File f : files) { System.out.println(f.getName()); } } catch (Exception e) { e.printStackTrace(); } return true; } }); setDefaultCloseOperation(DISPOSE_ON_CLOSE); pack(); setVisible(true); } } To reproduce, run the code and drop some files on the frame. Close the frame so it's disposed of. To verify the leak I take a heap dump using JConsole and analyse it with the Eclipse Memory Analysis tool. It shows that sun.awt.AppContext is holding a reference to the frame through its hashmap. It looks like TransferSupport is at fault. What am I doing wrong? Should I be asking the DnD support code to clean itself up somehow? I'm running JDK 1.6 update 19.

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• Basic Custom String Class for C++

  - by wdow88

  Hey all, I'm working on building my own string class with very basic functionality. I am having difficulty understand what is going on with the basic class that I have define, and believe there is some sort of error dealing with the scope occurring. When I try to view the objects I created, all the fields are described as (obviously bad pointer). Also, if I make the data fields public or build an accessor method, the program crashes. For some reason the pointer for the object is 0xccccccccc which points to no where. How can a I fix this? Any help/comments are much appreciated. //This is a custom string class, so far the only functions are //constructing and appending #include<iostream> using namespace std; class MyString1 { public: MyString1() { //no arg constructor char *string; string = new char[0]; string[0] ='\0'; std::cout << string; size = 1; } //constructor receives pointer to character array MyString1(char* chars) { int index = 0; //Determine the length of the array while (chars[index] != NULL) index++; //Allocate dynamic memory on the heap char *string; string = new char[index+1]; //Copy the contents of the array pointed by chars into string, the char array of the object for (int ii = 0; ii < index; ii++) string[ii] = chars[ii]; string[index+1] = '\0'; size = index+1; } MyString1 append(MyString1 s) { //determine new size of the appended array and allocate memory int newsize = s.size + size; MyString1 MyString2; char *newstring; newstring = new char[newsize+1]; int index = 0; //load the first string into the array while (string[index] != NULL) { newstring[index] = string[index]; index++; } //load the second string while (s.string[index] != NULL) { newstring[index] = s.string[index]; index++; } //null terminate newstring[newsize+1] = '\0'; delete string; //generate the object for return MyString2.string=newstring; MyString2.size=newsize; return MyString2; } private: char *string; int size; }; int main() { MyString1 string1; MyString1 string2("Hello There"); MyString1 string3("Buddy"); string2.append(string3); return 0; }

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• StringBuffer wont read whole stream into a string (JAVA/Android)

  - by Levara

  Hi all! I'm making an android program that retrieves content of a webpage using HttpURLConnection. I'm new to both Java and Android. Problem is: Reader reads whole page source, but in the last while iteration it doesn't append to stringBuffer that last part. Using debbuger I have determined that, in the last loop iteration, string buff is created, but stringBuffer just doesnt append it. I need to parse retrieved content. Is there any better way to handle the content for parsing than using strings. I've read on numerous other sites that string size in Java is limited only by available heap size. I've tried with StringBuilder too. Anyone know what could be the problem. Btw feel free to suggest any improvements to the code. Thanks! URL u; try { u = new URL("http://feeds.timesonline.co.uk/c/32313/f/440134/index.rss"); HttpURLConnection c = (HttpURLConnection) u.openConnection(); c.setRequestProperty("User-agent","Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322; InfoPath.1; .NET CLR 2.0.50727)"); c.setRequestMethod("GET"); c.setDoOutput(true); c.setReadTimeout(3000); c.connect(); StringBuffer stringBuffer = new StringBuffer(""); InputStream in = c.getInputStream(); InputStreamReader inp = new InputStreamReader(in); BufferedReader reader = new BufferedReader(inp); char[] buffer = new char[3072]; int len1 = 0; while ( (len1 = reader.read(buffer)) != -1 ) { String buff = new String(buffer,0,len1); stringBuffer.append(buff); } String stranica = new String(stringBuffer); c.disconnect(); reader.close(); inp.close(); in.close();

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• File using .net sockets, transferring problem

  - by Sergei

  I have a client and server, client sending file to server. When i transfer files on my computer(in local) everything is ok(try to sen file over 700mb). When i try to sent file use Internet to my friend in the end of sending appears error on server "Input string is not in correct format".This error appears in this expression fSize = Convert::ToUInt64(tokenes[0]); - and i don't mind wht it's appear. File should be transfered and wait other transferring ps: sorry for too much code, but i want to find solution private: void CreateServer() { try{ IPAddress ^ipAddres = IPAddress::Parse(ipAdress); listener = gcnew System::Net::Sockets::TcpListener(ipAddres, port); listener->Start(); clientsocket =listener->AcceptSocket(); bool keepalive = true; array<wchar_t,1> ^split = gcnew array<wchar_t>(1){ '\0' }; array<wchar_t,1> ^split2 = gcnew array<wchar_t>(1){ '|' }; statusBar1->Text = "Connected" ; // while (keepalive) { array<Byte>^ size1 = gcnew array<Byte>(1024); clientsocket->Receive(size1); System::String ^notSplited = System::Text::Encoding::GetEncoding(1251)->GetString(size1); array<String^> ^ tokenes = notSplited->Split(split2); System::String ^fileName = tokenes[1]->ToString(); statusBar1->Text = "Receiving file" ; unsigned long fSize = 0; //IN THIS EXPRESSIN APPEARS ERROR fSize = Convert::ToUInt64(tokenes[0]); if (!Directory::Exists("Received")) Directory::CreateDirectory("Received"); System::String ^path = "Received\\"+ fileName; while (File::Exists(path)) { int dotPos = path->LastIndexOf('.'); if (dotPos == -1) { path += "[1]"; } else { path = path->Insert(dotPos, "[1]"); } } FileStream ^fs = gcnew FileStream(path, FileMode::CreateNew, FileAccess::Write); BinaryWriter ^f = gcnew BinaryWriter(fs); //bytes received unsigned long processed = 0; pBarFilesTr->Visible = true; pBarFilesTr->Minimum = 0; pBarFilesTr->Maximum = (int)fSize; // Set the initial value of the ProgressBar. pBarFilesTr->Value = 0; pBarFilesTr->Step = 1024; //loop for receive file array<Byte>^ buffer = gcnew array<Byte>(1024); while (processed < fSize) { if ((fSize - processed) < 1024) { int bytes ; array<Byte>^ buf = gcnew array<Byte>(1024); bytes = clientsocket->Receive(buf); if (bytes != 0) { f->Write(buf, 0, bytes); processed = processed + (unsigned long)bytes; pBarFilesTr->PerformStep(); } break; } else { int bytes = clientsocket->Receive(buffer); if (bytes != 0) { f->Write(buffer, 0, 1024); processed = processed + 1024; pBarFilesTr->PerformStep(); } else break; } } statusBar1->Text = "File was received" ; array<Byte>^ buf = gcnew array<Byte>(1); clientsocket->Send(buf,buf->Length,SocketFlags::None); f->Close(); fs->Close(); SystemSounds::Beep->Play(); } }catch(System::Net::Sockets::SocketException ^es) { MessageBox::Show(es->ToString()); } catch(System::Exception ^es) { MessageBox::Show(es->ToString()); } } private: void CreateClient() { clientsock = gcnew System::Net::Sockets::TcpClient(ipAdress, port); ns = clientsock->GetStream(); sr = gcnew StreamReader(ns); statusBar1->Text = "Connected" ; } private:void Send() { try{ OpenFileDialog ^openFileDialog1 = gcnew OpenFileDialog(); System::String ^filePath = ""; System::String ^fileName = ""; //file choose dialog if (openFileDialog1->ShowDialog() == System::Windows::Forms::DialogResult::OK) { filePath = openFileDialog1->FileName; fileName = openFileDialog1->SafeFileName; } else { MessageBox::Show("You must select a file", "Error", MessageBoxButtons::OK, MessageBoxIcon::Exclamation); return; } statusBar1->Text = "Sending file" ; NetworkStream ^writerStream = clientsock->GetStream(); System::Runtime::Serialization::Formatters::Binary::BinaryFormatter ^format = gcnew System::Runtime::Serialization::Formatters::Binary::BinaryFormatter(); array<Byte>^ buffer = gcnew array<Byte>(1024); FileStream ^fs = gcnew FileStream(filePath, FileMode::Open); BinaryReader ^br = gcnew BinaryReader(fs); //file size unsigned long fSize = (unsigned long)fs->Length; //transfer file size + name bFSize = Encoding::GetEncoding(1251)->GetBytes(Convert::ToString(fs->Length+"|"+fileName+"|")); writerStream->Write(bFSize, 0, bFSize->Length); //status bar pBarFilesTr->Visible = true; pBarFilesTr->Minimum = 0; pBarFilesTr->Maximum = (int)fSize; pBarFilesTr->Value = 0; // Set the initial value of the ProgressBar. pBarFilesTr->Step = 1024; //bytes transfered unsigned long processed = 0; int bytes = 1024; //loop for transfer while (processed < fSize) { if ((fSize - processed) < 1024) { bytes = (int)(fSize - processed); array<Byte>^ buf = gcnew array<Byte>(bytes); br->Read(buf, 0, bytes); writerStream->Write(buf, 0, buf->Length); pBarFilesTr->PerformStep(); processed = processed + (unsigned long)bytes; break; } else { br->Read(buffer, 0, 1024); writerStream->Write(buffer, 0, buffer->Length); pBarFilesTr->PerformStep(); processed = processed + 1024; } } array<Byte>^ bufsss = gcnew array<Byte>(100); writerStream->Read(bufsss,0,bufsss->Length); statusBar1->Text = "File was sent" ; btnSend->Enabled = true; fs->Close(); br->Close(); SystemSounds::Beep->Play(); newThread->Abort(); } catch(System::Net::Sockets::SocketException ^es) { MessageBox::Show(es->ToString()); } } UPDATE: ok, i can add checking if clientsocket->Receive(size1); equal zero, but why he begin receiving data again , in the ending of receiving. UPDATE:After adding this checking problem remains. AND WIN RAR SAY TO OPENING ARCHIVE - unexpected end of file! UPDATE:http://img153.imageshack.us/img153/3760/erorr.gif I think it continue receiving some bytes from client(that remains in the stream), but why existes cicle while (processed < fSize)

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• Learning... anything really

  - by WebDevHobo

  I'm particularly interested in Windows PowerShell, but here's a somewhat more general complaint: When asking for help on learning something new, be it a small subject on PHP or understanding a class in Java, what usually happens is that people direct me towards the documentation pages. What I'm looking for is somewhat of a course. A deep explanation of why something works the way it does. I know my basic programming, like Java and C#. I've never seen C or C++, though I have seen a bit of assembler. I know what the Stack and Heap are, how boxing and unboxing works, why you have to deep-copy an array instead of copying the pointer and some other things. Windows PowerShell on the other hand, I know nothing about. And I notice that when reading the small document or some code, I usually forget what it does or why it works. What I am looking for is preferably, a nice tutorial that explains the beginnings, the concepts, and goes to more difficult things at a steady pace. The only thing documentation can do is explain what a function does. That's no good to me since I don't know what I want to do yet. I could read about a thousand functions, and forget about most of them, because I don't need to implement them right after it. Randomly wandering through the documentation doesn't do me any good. So conclude, what is a good tutorial on Windows Powershell? One which explains in clear language what is happening, one which builds on previous things learned. I don't think googling this is a good idea. Doing a Google search on this would turn up numerous tutorials. And experience tells me that you have to look long and hard to find the gem you're looking for. That's why I'm asking here. Because this is the place where you can find more experienced people. Many of the PowerShell guys among you will know the good ones already, and by asking you, I avoid wasting time that could be spent learning. So to summarize: I will not google this!

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• How do I create a thread-safe write-once read-many value in Java?

  - by Software Monkey

  This is a problem I encounter frequently in working with more complex systems and which I have never figured out a good way to solve. It usually involves variations on the theme of a shared object whose construction and initialization are necessarily two distinct steps. This is generally because of architectural requirements, similar to applets, so answers that suggest I consolidate construction and initialization are not useful. By way of example, let's say I have a class that is structured to fit into an application framework like so: public class MyClass { private /*ideally-final*/ SomeObject someObject; MyClass() { someObject=null; } public void startup() { someObject=new SomeObject(...arguments from environment which are not available until startup is called...); } public void shutdown() { someObject=null; // this is not necessary, I am just expressing the intended scope of someObject explicitly } } I can't make someObject final since it can't be set until startup() is invoked. But I would really like it to reflect it's write-once semantics and be able to directly access it from multiple threads, preferably avoiding synchronization. The idea being to express and enforce a degree of finalness, I conjecture that I could create a generic container, like so: public class WoRmObject<T> { private T object; WoRmObject() { object=null; } public WoRmObject set(T val) { object=val; return this; } public T get() { return object; } } and then in MyClass, above, do: private final WoRmObject<SomeObject> someObject; MyClass() { someObject=new WoRmObject<SomeObject>(); } public void startup() { someObject.set(SomeObject(...arguments from environment which are not available until startup is called...)); } Which raises some questions for me: Is there a better way, or existing Java object (would have to be available in Java 4)? Is this thread-safe provided that no other thread accesses someObject.get() until after it's set() has been called. The other threads will only invoke methods on MyClass between startup() and shutdown() - the framework guarantees this. Given the completely unsynchronized WoRmObject container, it is ever possible under either JMM to see a value of object which is neither null nor a reference to a SomeObject? In other words, does has the JMM always guaranteed that no thread can observe the memory of an object to be whatever values happened to be on the heap when the object was allocated.

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• Python - pickling fails for numpy.void objects

  - by I82Much

  >>> idmapfile = open("idmap", mode="w") >>> pickle.dump(idMap, idmapfile) >>> idmapfile.close() >>> idmapfile = open("idmap") >>> unpickled = pickle.load(idmapfile) >>> unpickled == idMap False idMap[1] {1537: (552, 1, 1537, 17.793827056884766, 3), 1540: (4220, 1, 1540, 19.31205940246582, 3), 1544: (592, 1, 1544, 18.129131317138672, 3), 1675: (529, 1, 1675, 18.347782135009766, 3), 1550: (4048, 1, 1550, 19.31205940246582, 3), 1424: (1528, 1, 1424, 19.744396209716797, 3), 1681: (1265, 1, 1681, 19.596025466918945, 3), 1560: (3457, 1, 1560, 20.530569076538086, 3), 1690: (477, 1, 1690, 17.395542144775391, 3), 1691: (554, 1, 1691, 13.446117401123047, 3), 1436: (3010, 1, 1436, 19.596025466918945, 3), 1434: (3183, 1, 1434, 19.744396209716797, 3), 1441: (3570, 1, 1441, 20.589576721191406, 3), 1435: (476, 1, 1435, 19.640911102294922, 3), 1444: (527, 1, 1444, 17.98480224609375, 3), 1478: (1897, 1, 1478, 19.596025466918945, 3), 1575: (614, 1, 1575, 19.371648788452148, 3), 1586: (2189, 1, 1586, 19.31205940246582, 3), 1716: (3470, 1, 1716, 19.158674240112305, 3), 1590: (2278, 1, 1590, 19.596025466918945, 3), 1463: (991, 1, 1463, 19.31205940246582, 3), 1594: (1890, 1, 1594, 19.596025466918945, 3), 1467: (1087, 1, 1467, 19.31205940246582, 3), 1596: (3759, 1, 1596, 19.744396209716797, 3), 1602: (3011, 1, 1602, 20.530569076538086, 3), 1547: (490, 1, 1547, 17.994071960449219, 3), 1605: (658, 1, 1605, 19.31205940246582, 3), 1606: (1794, 1, 1606, 16.964881896972656, 3), 1719: (1826, 1, 1719, 19.596025466918945, 3), 1617: (583, 1, 1617, 11.894925117492676, 3), 1492: (3441, 1, 1492, 20.500667572021484, 3), 1622: (3215, 1, 1622, 19.31205940246582, 3), 1628: (2761, 1, 1628, 19.744396209716797, 3), 1502: (1563, 1, 1502, 19.596025466918945, 3), 1632: (1108, 1, 1632, 15.457141876220703, 3), 1468: (3779, 1, 1468, 19.596025466918945, 3), 1642: (3970, 1, 1642, 19.744396209716797, 3), 1518: (612, 1, 1518, 18.570245742797852, 3), 1647: (854, 1, 1647, 16.964881896972656, 3), 1650: (2099, 1, 1650, 20.439058303833008, 3), 1651: (540, 1, 1651, 18.552841186523438, 3), 1653: (613, 1, 1653, 19.237197875976563, 3), 1532: (537, 1, 1532, 18.885730743408203, 3)} >>> unpickled[1] {1537: (64880, 1638, 56700, -1.0808743559293829e+18, 152), 1540: (64904, 1638, 0, 0.0, 0), 1544: (54472, 1490, 0, 0.0, 0), 1675: (6464, 1509, 0, 0.0, 0), 1550: (43592, 1510, 0, 0.0, 0), 1424: (43616, 1510, 0, 0.0, 0), 1681: (0, 0, 0, 0.0, 0), 1560: (400, 152, 400, 2.1299736657737219e-43, 0), 1690: (408, 152, 408, 2.7201111331839077e+26, 34), 1435: (424, 152, 61512, 1.0122952080313192e-39, 0), 1436: (400, 152, 400, 20.250289916992188, 3), 1434: (424, 152, 62080, 1.0122952080313192e-39, 0), 1441: (400, 152, 400, 12.250144958496094, 3), 1691: (424, 152, 42608, 15.813941955566406, 3), 1444: (400, 152, 400, 19.625289916992187, 3), 1606: (424, 152, 42432, 5.2947192852601414e-22, 41), 1575: (400, 152, 400, 6.2537390010262572e-36, 0), 1586: (424, 152, 42488, 1.0122601755697111e-39, 0), 1716: (400, 152, 400, 6.2537390010262572e-36, 0), 1590: (424, 152, 64144, 1.0126357235581501e-39, 0), 1463: (400, 152, 400, 6.2537390010262572e-36, 0), 1594: (424, 152, 32672, 17.002994537353516, 3), 1467: (400, 152, 400, 19.750289916992187, 3), 1596: (424, 152, 7176, 1.0124003054161436e-39, 0), 1602: (400, 152, 400, 18.500289916992188, 3), 1547: (424, 152, 7000, 1.0124003054161436e-39, 0), 1605: (400, 152, 400, 20.500289916992188, 3), 1478: (424, 152, 42256, -6.0222748507426518e+30, 222), 1719: (400, 152, 400, 6.2537390010262572e-36, 0), 1617: (424, 152, 16472, 1.0124283313854301e-39, 0), 1492: (400, 152, 400, 6.2537390010262572e-36, 0), 1622: (424, 152, 35304, 1.0123190301052127e-39, 0), 1628: (400, 152, 400, 6.2537390010262572e-36, 0), 1502: (424, 152, 63152, 19.627988815307617, 3), 1632: (400, 152, 400, 19.375289916992188, 3), 1468: (424, 152, 38088, 1.0124213248931084e-39, 0), 1642: (400, 152, 400, 6.2537390010262572e-36, 0), 1518: (424, 152, 63896, 1.0127436235399031e-39, 0), 1647: (400, 152, 400, 6.2537390010262572e-36, 0), 1650: (424, 152, 53424, 16.752857208251953, 3), 1651: (400, 152, 400, 19.250289916992188, 3), 1653: (424, 152, 50624, 1.0126497365427934e-39, 0), 1532: (400, 152, 400, 6.2537390010262572e-36, 0)} The keys come out fine, the values are screwed up. I tried same thing loading file in binary mode; didn't fix the problem. Any idea what I'm doing wrong? Edit: Here's the code with binary. Note that the values are different in the unpickled object. >>> idmapfile = open("idmap", mode="wb") >>> pickle.dump(idMap, idmapfile) >>> idmapfile.close() >>> idmapfile = open("idmap", mode="rb") >>> unpickled = pickle.load(idmapfile) >>> unpickled==idMap False >>> unpickled[1] {1537: (12176, 2281, 56700, -1.0808743559293829e+18, 152), 1540: (0, 0, 15934, 2.7457842047810522e+26, 108), 1544: (400, 152, 400, 4.9518498821046956e+27, 53), 1675: (408, 152, 408, 2.7201111331839077e+26, 34), 1550: (456, 152, 456, -1.1349175514578289e+18, 152), 1424: (432, 152, 432, 4.5939047815653343e-40, 11), 1681: (408, 152, 408, 2.1299736657737219e-43, 0), 1560: (376, 152, 376, 2.1299736657737219e-43, 0), 1690: (376, 152, 376, 2.1299736657737219e-43, 0), 1435: (376, 152, 376, 2.1299736657737219e-43, 0), 1436: (376, 152, 376, 2.1299736657737219e-43, 0), 1434: (376, 152, 376, 2.1299736657737219e-43, 0), 1441: (376, 152, 376, 2.1299736657737219e-43, 0), 1691: (376, 152, 376, 2.1299736657737219e-43, 0), 1444: (376, 152, 376, 2.1299736657737219e-43, 0), 1606: (25784, 2281, 376, -3.2883343074537754e+26, 34), 1575: (24240, 2281, 376, 2.1299736657737219e-43, 0), 1586: (24240, 2281, 376, 2.1299736657737219e-43, 0), 1716: (24240, 2281, 376, -3.0093091599657311e-35, 26), 1590: (24240, 2281, 376, 2.1299736657737219e-43, 0), 1463: (24240, 2281, 376, 2.1299736657737219e-43, 0), 1594: (24240, 2281, 376, -4123208450048.0, 196), 1467: (25784, 2281, 376, 2.1299736657737219e-43, 0), 1596: (25784, 2281, 376, 2.1299736657737219e-43, 0), 1602: (25784, 2281, 376, -5.9963281433905448e+26, 76), 1547: (25784, 2281, 376, -218106240.0, 139), 1605: (25784, 2281, 376, -3.7138649803377281e+27, 56), 1478: (376, 152, 376, 2.1299736657737219e-43, 0), 1719: (25784, 2281, 376, 2.1299736657737219e-43, 0), 1617: (25784, 2281, 376, -1.4411779941597184e+17, 237), 1492: (25784, 2281, 376, 2.8596493694487798e-30, 80), 1622: (25784, 2281, 376, 184686084096.0, 93), 1628: (1336, 152, 1336, 3.1691839245470052e+29, 179), 1502: (1272, 152, 1272, -5.2042207205116645e-17, 99), 1632: (1208, 152, 1208, 2.1299736657737219e-43, 0), 1468: (1144, 152, 1144, 2.1299736657737219e-43, 0), 1642: (1080, 152, 1080, 2.1299736657737219e-43, 0), 1518: (1016, 152, 1016, 4.0240902787680023e+35, 145), 1647: (952, 152, 952, -985172619034624.0, 237), 1650: (888, 152, 888, 12094787289088.0, 66), 1651: (824, 152, 824, 2.1299736657737219e-43, 0), 1653: (760, 152, 760, 0.00018310768064111471, 238), 1532: (696, 152, 696, 8.8978061885676389e+26, 125)} OK I've isolated the problem, but don't know why it's so. First, apparently what I'm pickling are not tuples (though they look like it), but instead numpy.void types. Here is a series to illustrate the problem. first = run0.detections[0] >>> first (1, 19, 1578, 82.637763977050781, 1) >>> type(first) <type 'numpy.void'> >>> firstTuple = tuple(first) >>> theFile = open("pickleTest", "w") >>> pickle.dump(first, theFile) >>> theTupleFile = open("pickleTupleTest", "w") >>> pickle.dump(firstTuple, theTupleFile) >>> theFile.close() >>> theTupleFile.close() >>> first (1, 19, 1578, 82.637763977050781, 1) >>> firstTuple (1, 19, 1578, 82.637764, 1) >>> theFile = open("pickleTest", "r") >>> theTupleFile = open("pickleTupleTest", "r") >>> unpickledTuple = pickle.load(theTupleFile) >>> unpickledVoid = pickle.load(theFile) >>> type(unpickledVoid) <type 'numpy.void'> >>> type(unpickledTuple) <type 'tuple'> >>> unpickledTuple (1, 19, 1578, 82.637764, 1) >>> unpickledTuple == firstTuple True >>> unpickledVoid == first False >>> unpickledVoid (7936, 1705, 56700, -1.0808743559293829e+18, 152) >>> first (1, 19, 1578, 82.637763977050781, 1)

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• File using sockets .net, tranfering problem

  - by Sergei

  I have a client and server, client sending file to server. When i transfer files on my computer(in local) everything is ok(try to sen file over 700mb). When i try to sent file use Internet to my friend in the end of sending appears error on server "Input string is not in correct format".This error appears in this expression fSize = Convert::ToUInt64(tokenes[0]); - and i don't mind wht it's appear. File should be transfered and wait other transferring ps: sorry for too much code, but i want to find solution private: void CreateServer() { try{ IPAddress ^ipAddres = IPAddress::Parse(ipAdress); listener = gcnew System::Net::Sockets::TcpListener(ipAddres, port); listener->Start(); clientsocket =listener->AcceptSocket(); bool keepalive = true; array<wchar_t,1> ^split = gcnew array<wchar_t>(1){ '\0' }; array<wchar_t,1> ^split2 = gcnew array<wchar_t>(1){ '|' }; statusBar1->Text = "Connected" ; // while (keepalive) { array<Byte>^ size1 = gcnew array<Byte>(1024); clientsocket->Receive(size1); System::String ^notSplited = System::Text::Encoding::GetEncoding(1251)->GetString(size1); array<String^> ^ tokenes = notSplited->Split(split2); System::String ^fileName = tokenes[1]->ToString(); statusBar1->Text = "Receiving file" ; unsigned long fSize = 0; //IN THIS EXPRESSIN APPEARS ERROR fSize = Convert::ToUInt64(tokenes[0]); if (!Directory::Exists("Received")) Directory::CreateDirectory("Received"); System::String ^path = "Received\\"+ fileName; while (File::Exists(path)) { int dotPos = path->LastIndexOf('.'); if (dotPos == -1) { path += "[1]"; } else { path = path->Insert(dotPos, "[1]"); } } FileStream ^fs = gcnew FileStream(path, FileMode::CreateNew, FileAccess::Write); BinaryWriter ^f = gcnew BinaryWriter(fs); //bytes received unsigned long processed = 0; pBarFilesTr->Visible = true; pBarFilesTr->Minimum = 0; pBarFilesTr->Maximum = (int)fSize; // Set the initial value of the ProgressBar. pBarFilesTr->Value = 0; pBarFilesTr->Step = 1024; //loop for receive file array<Byte>^ buffer = gcnew array<Byte>(1024); while (processed < fSize) { if ((fSize - processed) < 1024) { int bytes ; array<Byte>^ buf = gcnew array<Byte>(1024); bytes = clientsocket->Receive(buf); if (bytes != 0) { f->Write(buf, 0, bytes); processed = processed + (unsigned long)bytes; pBarFilesTr->PerformStep(); } break; } else { int bytes = clientsocket->Receive(buffer); if (bytes != 0) { f->Write(buffer, 0, 1024); processed = processed + 1024; pBarFilesTr->PerformStep(); } else break; } } statusBar1->Text = "File was received" ; array<Byte>^ buf = gcnew array<Byte>(1); clientsocket->Send(buf,buf->Length,SocketFlags::None); f->Close(); fs->Close(); SystemSounds::Beep->Play(); } }catch(System::Net::Sockets::SocketException ^es) { MessageBox::Show(es->ToString()); } catch(System::Exception ^es) { MessageBox::Show(es->ToString()); } } private: void CreateClient() { clientsock = gcnew System::Net::Sockets::TcpClient(ipAdress, port); ns = clientsock->GetStream(); sr = gcnew StreamReader(ns); statusBar1->Text = "Connected" ; } private:void Send() { try{ OpenFileDialog ^openFileDialog1 = gcnew OpenFileDialog(); System::String ^filePath = ""; System::String ^fileName = ""; //file choose dialog if (openFileDialog1->ShowDialog() == System::Windows::Forms::DialogResult::OK) { filePath = openFileDialog1->FileName; fileName = openFileDialog1->SafeFileName; } else { MessageBox::Show("You must select a file", "Error", MessageBoxButtons::OK, MessageBoxIcon::Exclamation); return; } statusBar1->Text = "Sending file" ; NetworkStream ^writerStream = clientsock->GetStream(); System::Runtime::Serialization::Formatters::Binary::BinaryFormatter ^format = gcnew System::Runtime::Serialization::Formatters::Binary::BinaryFormatter(); array<Byte>^ buffer = gcnew array<Byte>(1024); FileStream ^fs = gcnew FileStream(filePath, FileMode::Open); BinaryReader ^br = gcnew BinaryReader(fs); //file size unsigned long fSize = (unsigned long)fs->Length; //transfer file size + name bFSize = Encoding::GetEncoding(1251)->GetBytes(Convert::ToString(fs->Length+"|"+fileName+"|")); writerStream->Write(bFSize, 0, bFSize->Length); //status bar pBarFilesTr->Visible = true; pBarFilesTr->Minimum = 0; pBarFilesTr->Maximum = (int)fSize; pBarFilesTr->Value = 0; // Set the initial value of the ProgressBar. pBarFilesTr->Step = 1024; //bytes transfered unsigned long processed = 0; int bytes = 1024; //loop for transfer while (processed < fSize) { if ((fSize - processed) < 1024) { bytes = (int)(fSize - processed); array<Byte>^ buf = gcnew array<Byte>(bytes); br->Read(buf, 0, bytes); writerStream->Write(buf, 0, buf->Length); pBarFilesTr->PerformStep(); processed = processed + (unsigned long)bytes; break; } else { br->Read(buffer, 0, 1024); writerStream->Write(buffer, 0, buffer->Length); pBarFilesTr->PerformStep(); processed = processed + 1024; } } array<Byte>^ bufsss = gcnew array<Byte>(100); writerStream->Read(bufsss,0,bufsss->Length); statusBar1->Text = "File was sent" ; btnSend->Enabled = true; fs->Close(); br->Close(); SystemSounds::Beep->Play(); newThread->Abort(); } catch(System::Net::Sockets::SocketException ^es) { MessageBox::Show(es->ToString()); } }

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• C++: Trouble with Pointers, loop variables, and structs

  - by Rosarch

  Consider the following example: #include <iostream> #include <sstream> #include <vector> #include <wchar.h> #include <stdlib.h> using namespace std; struct odp { int f; wchar_t* pstr; }; int main() { vector<odp> vec; ostringstream ss; wchar_t base[5]; wcscpy_s(base, L"1234"); for (int i = 0; i < 4; i++) { odp foo; foo.f = i; wchar_t loopStr[1]; foo.pstr = loopStr; // wchar_t* = wchar_t ? Why does this work? foo.pstr[0] = base[i]; vec.push_back(foo); } for (vector<odp>::iterator iter = vec.begin(); iter != vec.end(); iter++) { cout << "Vec contains: " << iter->f << ", " << *(iter->pstr) << endl; } } This produces: Vec contains: 0, 52 Vec contains: 1, 52 Vec contains: 2, 52 Vec contains: 3, 52 I would hope that each time, iter->f and iter->pstr would yield a different result. Unfortunately, iter->pstr is always the same. My suspicion is that each time through the loop, a new loopStr is created. Instead of copying it into the struct, I'm only copying a pointer. The location that the pointer writes to is getting overwritten. How can I avoid this? Is it possible to solve this problem without allocating memory on the heap?

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• Understanding C++ dynamic allocation

  - by kiokko89

  Consider the following code: class CString { private: char* buff; size_t len; public: CString(const char* p):len(0), buff(nullptr) { cout << "Constructor called!"<<endl; if (p!=nullptr) { len= strlen(p); if (len>0) { buff= new char[len+1]; strcpy_s(buff, len+1, p); } } } CString (const CString& s) { cout << "Copy constructor called!"<<endl; len= s.len; buff= new char[len+1]; strcpy_s(buff, len+1, s.buff); } CString& operator = (const CString& rhs) { cout << "Assignment operator called!"<<endl; if (this != &rhs) { len= rhs.len; delete[] buff; buff= new char[len+1]; strcpy_s(buff, len+1, rhs.buff); } return *this; } CString operator + (const CString& rhs) const { cout << "Addition operator called!"<<endl; size_t lenght= len+rhs.len+1; char* tmp = new char[lenght]; strcpy_s(tmp, lenght, buff); strcat_s(tmp, lenght, rhs.buff); return CString(tmp); } ~CString() { cout << "Destructor called!"<<endl; delete[] buff; } }; int main() { CString s1("Hello"); CString s2("World"); CString s3 = s1+s2; } My problem is that I don't know how to delete the memory allocated in the addition operator function(char* tmp = new char[length]). I couldn't do this in the constructor(I tried delete[] p) because it is also called from the main function with arrays of chars as parameters which are not allocated on the heap...How can I get around this? (Sorry for my bad English...)

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• WinForm-style Invoke() in unmanaged C++

  - by Matt Green

  I've been playing with a DataBus-type design for a hobby project, and I ran into an issue. Back-end components need to notify the UI that something has happened. My implementation of the bus delivers the messages synchronously with respect to the sender. In other words, when you call Send(), the method blocks until all the handlers have called. (This allows callers to use stack memory management for event objects.) However, consider the case where an event handler updates the GUI in response to an event. If the handler is called, and the message sender lives on another thread, then the handler cannot update the GUI due to Win32's GUI elements having thread affinity. More dynamic platforms such as .NET allow you to handle this by calling a special Invoke() method to move the method call (and the arguments) to the UI thread. I'm guessing they use the .NET parking window or the like for these sorts of things. A morbid curiosity was born: can we do this in C++, even if we limit the scope of the problem? Can we make it nicer than existing solutions? I know Qt does something similar with the moveToThread() function. By nicer, I'll mention that I'm specifically trying to avoid code of the following form: if(! this->IsUIThread()) { Invoke(MainWindowPresenter::OnTracksAdded, e); return; } being at the top of every UI method. This dance was common in WinForms when dealing with this issue. I think this sort of concern should be isolated from the domain-specific code and a wrapper object made to deal with it. My implementation consists of: DeferredFunction - functor that stores the target method in a FastDelegate, and deep copies the single event argument. This is the object that is sent across thread boundaries. UIEventHandler - responsible for dispatching a single event from the bus. When the Execute() method is called, it checks the thread ID. If it does not match the UI thread ID (set at construction time), a DeferredFunction is allocated on the heap with the instance, method, and event argument. A pointer to it is sent to the UI thread via PostThreadMessage(). Finally, a hook function for the thread's message pump is used to call the DeferredFunction and de-allocate it. Alternatively, I can use a message loop filter, since my UI framework (WTL) supports them. Ultimately, is this a good idea? The whole message hooking thing makes me leery. The intent is certainly noble, but are there are any pitfalls I should know about? Or is there an easier way to do this?

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• Printing a variable only when it changes?

  - by user1781639

  First off, my question was a little vague or confusing since I'm not really sure how to phrase my question to be specific. I'm trying to query a database of stockists for a Knitting company (school project using PHP) but I'm looking to print the city as a heading instead of with each stockists information. Here is what I have at the moment: $sql = "SELECT * FROM mc16korustockists where locale = 'south'"; $result = pg_exec($sql); $nrows = pg_numrows($result); print $nrows; $items = pg_fetch_all($result); print_r($items); for ($i=0; $i<$nrows2; $i++) { print "<h2>"; print $items[$i]['city']; print "</h2>"; print $items[$i]['name']; print $items[$i]['address']; print $items[$i]['city']; print $items[$i]['phone']; print "<br />"; print "<br />"; } I'm querying the database for all of the data in it, the rows being ref, name, address, city and phone, and executing it. Querying the number of rows then using that to determine how many iterations for the loop to run is all fine but what I'd like to have is for the h2 heading to appear above the for ($i=0;) line. Trying just breaks my page so that might be out of the question. I figure I'd have to count the number of entries in 'city' until it detects a change then change the heading to that name I think? That or make a heap of queries and set a variable for each name but at point, I might as well do it manually (and I highly doubt it would be best practice). Oh, and I'd welcome any critiques to my PHP since I'm just starting out. Thanks and if you need any more information, just ask! P.S. Our class is learning with PostgreSQL instead of MySQL as you can see in the tags.

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• Can I use the [] operator in C++ to create virtual arrays

  - by Shane MacLaughlin

  I have a large code base, originally C ported to C++ many years ago, that is operating on a number of large arrays of spatial data. These arrays contain structs representing point and triangle entities that represent surface models. I need to refactor the code such that the specific way these entities are stored internally varies for specific scenarios. For example if the points lie on a regular flat grid, I don't need to store the X and Y coordinates, as they can be calculated on the fly, as can the triangles. Similarly, I want to take advantage of out of core tools such as STXXL for storage. The simplest way of doing this is replacing array access with put and get type functions, e.g. point[i].x = XV; becomes Point p = GetPoint(i); p.x = XV; PutPoint(i,p); As you can imagine, this is a very tedious refactor on a large code base, prone to all sorts of errors en route. What I'd like to do is write a class that mimics the array by overloading the [] operator. As the arrays already live on the heap, and move around with reallocs, the code already assumes that references into the array such as point *p = point + i; may not be used. Is this class feasible to write? For example writing the methods below in terms of the [] operator; void MyClass::PutPoint(int Index, Point p) { if (m_StorageStrategy == RegularGrid) { int xoffs,yoffs; ComputeGridFromIndex(Index,xoffs,yoffs); StoreGridPoint(xoffs,yoffs,p.z); } else m_PointArray[Index] = p; } } Point MyClass::GetPoint(int Index) { if (m_StorageStrategy == RegularGrid) { int xoffs,yoffs; ComputeGridFromIndex(Index,xoffs,yoffs); return GetGridPoint(xoffs,yoffs); // GetGridPoint returns Point } else return m_PointArray[Index]; } } My concern is that all the array classes I've seen tend to pass by reference, whereas I think I'll have to pass structs by value. I think it should work put other than performance, can anyone see any major pitfalls with this approach. n.b. the reason I have to pass by value is to get point[a].z = point[b].z + point[c].z to work correctly where the underlying storage type varies.

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