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  • Is it legal for a C++ reference to be NULL?

    - by BCS
    A while back I ran into a bug the looked something like this: void fn(int &i) { printf(&i == NULL ? "NULL\n" : "!NULL\n"); } int main() { int i; int *ip = NULL; fn(i); // prints !NULL fn(*ip); // prints NULL return 0; } More recently, I ran into this comment about C++ references: [References arguments make] it clear, unlike with pointers, that NULL is not a possible value. But, as show above, NULL is a possible value. So where is the error? In the language spec? (Unlikely.) Is the compiler in error for allowing that? Is that coding guide in error (or a little ambiguous)? Or am I just wandering into the minefield known as undefined behavior?

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  • Dynamically creating/inserting into an associative array in PHP

    - by emil.mp
    I'm trying to build an associative array in PHP dynamically, and not quite getting my strategy right. Basically, I want to insert a value at a certain depth in the array structure, for instance: $array['first']['second']['third'] = $val; Now, the thing is, I'm not sure if that depth is available, and if it isn't, I want to create the keys (and arrays) for each level, and finally insert the value at the correct level. Since I'm doing this quite a lot in my code, I grew tired of doing a whole bunch of "array_key_exists", so I wanted to do a function that builds the array for me, given a list of the level keys. Any help on a good strategy for this is appreciated. I'm sure there is a pretty simple way, I'm just not getting it...

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  • IPTABLES syntax help to forward Remote Desktop requests to a VM [CentOS host]

    - by NVRAM
    I've a VM running MSWindows XP hosted on my CentOS 5.4 machine. I can rdesktop into it from the hosting machine and work just fine using the private ddress (192.168.122.65), but I now need to allow Remote Desktop access from other computers (not just the machine hosting the VM). [Edit] I only need to allow access for a day or so, so don't want to add a NIC (for XP activation reasons). Could someone help me with the iptables syntax? The VM is on a private/virtual network: 192.168.122.65 and my CentOS machine is on a physical network, at 10.1.3.38 (and 192.168.122.1 as the GW for the virtual net). I found this question, but none of the answers seemed to work and I'm a bit timid at blindly trying variations. My FORWARD rules are as listed. Thanks in advance. # iptables -L FORWARD Chain FORWARD (policy ACCEPT) target prot opt source destination ACCEPT all -- anywhere 192.168.122.0/24 state RELATED,ESTABLISHED ACCEPT all -- 192.168.122.0/24 anywhere ACCEPT all -- anywhere anywhere REJECT all -- anywhere anywhere reject-with icmp-port-unreachable REJECT all -- anywhere anywhere reject-with icmp-port-unreachable RH-Firewall-1-INPUT all -- anywhere anywhere [Edit] If I do play "blindly" is there a simple way to reset the settings on CentOS (a la service network restart)?

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  • How much faster are register based architectures than stack architectures?

    - by drozzy
    Studying compilers course, I am left wondering why use registers at all. It is often the case that the caller or callee must save the register value and then restore it. In a way they always end up using the stack anyway. Is creating additional complexity by using registers really worth it? Excuse my ignorance. Update: Please, I know that registers are faster than RAM and other types of cache. My main concern is that one has to "save" the value that is in the register and the "restore" it to. In both cases we are accessing some kind of cache. Would it not be better to use cache in the first place?

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  • How to ORDER BY non-column field?

    - by Phil Bolduc
    I am trying to create an Entity SQL that is a union of two sub-queries. (SELECT VALUE DISTINCT ROW(e.ColumnA, e.ColumnB, 1 AS Rank) FROM Context.Entity AS E WHERE ...) UNION ALL (SELECT VALUE DISTINCT ROW(e.ColumnA, e.ColumnB, 2 AS Rank) FROM Context.Entity AS E WHERE ...) ORDER BY *??* LIMIT 50 I have tried: ORDER BY Rank and ORDER BY e.Rank but I keep getting: System.Data.EntitySqlException: The query syntax is not valid. Near keyword 'ORDER' I do not think it is a problem with the Rank column. I do think it is how I am trying to apply an order by to two different esql statements joined by union all. Could someone suggest: How to apply a ORDER BY to this kind of UNION/UNION ALL statment How to order by the non-entity column expression. Thanks.

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  • what's a good way to implement something that looks like Dictionary<string, string, Dictionary<strin

    - by jcollum
    I've got a data structure that is Key, Value, OtherValues(key, Value). So the OtherValues are attached to the first Key and aren't always there. I can do this as Dictionary<Key, ValueAndListOfOptionalValues> where ValueAndListOfOptionalValues is a class with a string and a Dictionary<string, string>. I'm wondering if that's really the best way to do it? Sometimes I think that I'm missing some important classes in the Generics namespace, maybe there are better classes out there that I'm not aware of.

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  • Javascript function programming — receiving elaborate parameters

    - by Barney
    I'm writing a Javascript function that would manipulate an array written on-the-fly and sent as a parameter. The function is written as follows: function returnJourney(animation,clean){ var properties = {}; // loads of other inane stuff for(i in animation[0]) properties[animation[0][i]] = animation[0].i; // heaps more inane stuff } The animation in question is a set of parameters for a jQuery animation. Typically it takes the format of ({key:value,key:value},speedAsInteger,modifierAsString). So to kick off initial debugging I call it with: returnJouney(({'foo':'bar'},3000),1); And straight off the bat things are way off. As far as I see it this would have returnJourney acknowledge clean === 1, and animation being an array with an object as its first child and the number 3000 as its second. Firebug tells me animation evaluates as the number 3000. What am I doing wrong?

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  • Help in setting the setClientInfo with JPA

    - by enrique
    i am trying to set to jpa the new JDBC method which allows the application to be identified with a name it is the setClientInfo() and i could do it using pure JDBC using the lines Properties jdbcProperties = new Properties(); jdbcProperties.put("user", "system"); jdbcProperties.put("password", "sw01"); jdbcProperties.put("v$session.program", "Clients"); Connection connection = DriverManager.getConnection(url,jdbcProperties); However i have new requirements and i need to make it with JPA EclipseLink i have been googling and could not find something substantial on how to set this property out in JPA i guess it is by annotating something but i do not know what, i was trying to setting the persistence unit by putting the following in the persistence unit: <properties> <property name="toplink.ddl-generation" value="create-tables"/> <property name="v$session.program" value="Clients"/> </properties> but no lucky ...does somebody know how to do it or any idea...? thanks in advanced.-

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  • Create an event to recognise when text on a page changes?

    - by DaveDev
    There's a page that I'm trying to trigger a jQuery event for when a certain span's value changes to 1. There's a countdown timer on the page. When the timer reaches 1, I'd like to trigger a click event. The difficulty I'm having is getting a script that i'm running via Jash to know when the timer changes to 1. The value of the timer can read with: $('#tCounter_474754 .bid_time_highlight').text(); But how can I get jQuery to trigger the click when this timer reaches 1?

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  • Problem intialising 2D array

    - by TeeJay
    Ok, so I have a 2D Array that is initialised with values from a file (format: x y z). My file reads in the values correctly but when adding the z value to the matrix/2DArray, I run into a segfault and I have no idea why. It is possibly incorrect use of pointers? I still don't quite have the hang of them yet. This is my intialiser, works fine, even intialises all "z" values to 0. int** make2DArray(int rows, int columns) { int** newArray; newArray = (int**)malloc(rows*sizeof(int*)); if (newArray == NULL) { printf("out of memory for newArray.\n"); } for (int i = 0; i < rows; i++) { newArray[i] = (int*)malloc(columns*sizeof(int)); if (newArray[i] == NULL) { printf("out of memory for newArray[%d].\n", i); } } //intialise all values to 0 for (int i = 0; i < rows; i++) { for (int j = 0; j < columns; j++) { newArray[i][j] = 0; } } return newArray; } This is how I call the initialiser (and problem function). int** map = make2DArray(rows, columns); fillMatrix(&map, mapFile); And this is the problem code. void fillMatrix(int*** inMatrix, FILE* inFile) { int x, y, z; char line[100]; while(fgets(line, sizeof(line), inFile) != NULL) { sscanf(line, "%d %d %d", &x, &y, &z); *inMatrix[x][y] = z; } } From what I can gather through the use of ddd, the problem comes when y gets to 47. The map file has a max "x" value of 47 and a max "y" value of 63, I'm pretty sure I haven't got the order mixed up, so I don't know why the program is segfault-ing? I'm sure it's some newbie mistake...

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  • Three boolean values saved in one tinyint

    - by Casper
    Hello, probably a simple question but I seem to be suffering from programmer's block. :) I have three boolean values: A, B, and C. I would like to save the state combination as an unsigned tinyint (max 255) into a database and be able to derive the states from the saved integer. Even though there are only a limited number of combinations, I would like to avoid hard-coding each state combination to a specific value (something like if A=true and B=true has the value 1). I tried to assign values to the variables so (A=1, B=2, C=3) and then adding, but I can't differentiate between A and B being true from i.e. only C being true. I am stumped but pretty sure that it is possible. Thanks

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  • Best practice question

    - by sid_com
    Hello! Which version would you prefer? #!/usr/bin/env perl use warnings; use strict; use 5.010; my $p = 7; # 33 my $prompt = ' : '; my $key = 'very important text'; my $value = 'Hello, World!'; my $length = length $key . $prompt; $p -= $length; Option 1: $key = $key . ' ' x $p . $prompt; Option 2: if ( $p > 0 ) { $key = $key . ' ' x $p . $prompt; } else { $key = $key . $prompt; } say "$key$value"

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  • Why is Dictionary.First() so slow?

    - by Rotsor
    Not a real question because I already found out the answer, but still interesting thing. I always thought that hash table is the fastest associative container if you hash properly. However, the following code is terribly slow. It executes only about 1 million iterations and takes more than 2 minutes of time on a Core 2 CPU. The code does the following: it maintains the collection todo of items it needs to process. At each iteration it takes an item from this collection (doesn't matter which item), deletes it, processes it if it wasn't processed (possibly adding more items to process), and repeats this until there are no items to process. The culprit seems to be the Dictionary.Keys.First() operation. The question is why is it slow? Stopwatch watch = new Stopwatch(); watch.Start(); HashSet<int> processed = new HashSet<int>(); Dictionary<int, int> todo = new Dictionary<int, int>(); todo.Add(1, 1); int iterations = 0; int limit = 500000; while (todo.Count > 0) { iterations++; var key = todo.Keys.First(); var value = todo[key]; todo.Remove(key); if (!processed.Contains(key)) { processed.Add(key); // process item here if (key < limit) { todo[key + 13] = value + 1; todo[key + 7] = value + 1; } // doesn't matter much how } } Console.WriteLine("Iterations: {0}; Time: {1}.", iterations, watch.Elapsed); This results in: Iterations: 923007; Time: 00:02:09.8414388. Simply changing Dictionary to SortedDictionary yields: Iterations: 499976; Time: 00:00:00.4451514. 300 times faster while having only 2 times less iterations. The same happens in java. Used HashMap instead of Dictionary and keySet().iterator().next() instead of Keys.First().

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  • MySQL update query, how to skip empty values?

    - by Pawel
    I've got such query: $sql = "UPDATE test_accs SET acc_owner = '$owner_id', acc_policy_version = '$version', acc_policy_last_update = '$approved', acc_policy_next_update = '$renewed' WHERE acc_id = '1'"; Now, all of these values on the web folmular are optional, one can set one of these values, two, or so. Now, after I submit the form, it goes in the query like that: UPDATE test_accs SET acc_owner = '2', acc_policy_version = '1.2', acc_policy_last_update = '2012-12-19', acc_policy_next_update = '2012-12-18' WHERE acc_id = '1' It works only when I submit all values from the form. Can you please show me how could it work even if not all the values has been sent, just for example one of them? When I set one value (f.ex. policy version), it looks like that: UPDATE test_accs SET acc_owner = '', acc_policy_version = '1.2', acc_policy_last_update = '', acc_policy_next_update = '' WHERE acc_id = '1' and it isn't working. It might be possible cause of the acc_owner table values? #1366 - Incorrect integer value: '' for column 'acc_owner' at row 1 Thanks in advice.

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  • Why have private fields in data contracts modified through public ones?

    - by Nordvind
    When you make a new WCF project, sample service is generated for you. The default data contract is (I've just changed the string type field title): [DataContract] public class CompositeType { bool boolValue = true; string name = ""; [DataMember] public bool BoolValue { get { return boolValue; } set { boolValue = value; } } [DataMember] public string Name { get { return name; } set { name = value; } } } What is the point of having those private fields boolValue and name? Is it a good practice writing some data sanitizing or some other manipulations in contract, thus bloating it? It seems the only sane reason for me not writing to fields directly. So is it a bloatware or it has some reason behind it?

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  • Sum up values in SQL once all values are available

    - by James Brown
    I have events flowing into a MySQL database and I need to group and sum the events to transactions and store away into another table. The data looks like: +----+---------+------+-------+ | id | transid | code | value | +----+---------+------+-------+ | 1 | 1 | b | 12 | | 2 | 1 | i | 23 | | 3 | 2 | b | 34 | | 4 | 1 | e | 45 | | 5 | 3 | b | 56 | | 6 | 2 | i | 67 | | 7 | 2 | e | 78 | | 8 | 3 | i | 89 | | 9 | 3 | i | 90 | +----+---------+------+-------+ The events arrive in batches and I would like to create the transaction by summing up the values for each transid, like: select transid, sum(value) from eventtable group by transid; but only after all the events for that transid have arrived. That is determined by the event with the code e (b for the beginning, e for the end and i for varying amount of intermediates). Being a novice in SQL, how could I implement the requirement for the existance of the end code before the summing?

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  • Prevent printing -0

    - by fishinear
    If I do the following in Objective-C: NSString *result = [NSString stringWithFormat:@"%1.1f", -0.01]; It will give result @"-0.0" Does anybody know how I can force a result @"0.0" (without the "-") in this case? EDIT: I tried using NSNumberFormatter, but it has the same issue. The following also produces @"-0.0": double value = -0.01; NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init]; [numberFormatter setNumberStyle:NSNumberFormatterDecimalStyle]; [numberFormatter setMaximumFractionDigits:1]; [numberFormatter setMinimumFractionDigits:1]; NSString *result = [numberFormatter stringFromNumber:[NSNumber numberWithDouble:value]];

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  • How to get rid of "d»z" or "" characters

    - by Cassandra
    I have website based on Umbraco 5. I have installed contact form plugin (http://cultivjupitercontact.codeplex.com/). And on the web page at the end of this contact form there are always characters "d»z". It looks like that: ... <input type="submit" value="Send" /> </fieldset> <input name='uformpostroutevals' type='hidden' value='somevalue' /></form>d»z I suspect there is something wrong with encoding. I have tried to change it(to ANSI or UTF-8 without BOM but it didn't helped. Perhaps I have changed it in wrong file, cause I don't really know where exactly this 'd»z'is coming from. All I know it came with this plugin. On different server those extra characters are "". How can I get rid of those extra characters? Any help much appreciated!

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  • Updating a module level shared dictionary

    - by Vishal
    Hi, A module level dictionary 'd' and is accessed by different threads/requests in a django web application. I need to update 'd' every minute with a new data and the process takes about 5 seconds. What could be best solution where I want the users to get either the old value or the new value of d and nothing in between. I can think of a solution where a temp dictionary is constructed with a new data and assigned to 'd' but not sure how this works! Appreciate your ideas. Thanks

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  • Track only iframe history

    - by evanwong
    I have a page which contains an iframe and I want to track the history of the iframe only. I tried to use the history object like this: <!DOCTYPE html> <html> <head> <title></title> <script type="text/javascript"> function checkFrameHistory() { alert(window.frames["test2"].history.length); } function checkThisHistory() { alert(history.length); } </script> </head> <body> <iframe name="test2" src="test2.html"></iframe> <div> <input type="button" onclick="checkFrameHistory()" value="Frame history"/> <input type="button" onclick="checkThisHistory()" value="This history"/> </div> </body> </html> test2.html <!DOCTYPE html> <html> <head> <title></title> <script type="text/javascript"> function checkMyHistory() { alert(history.length); } </script> </head> <body> <div> Test2 </div> <div> <input type="button" onclick="checkMyHistory()" value="My history"/> </div> </body> </html> but it actually gave me the history including the parent window. For instance, I went to another site in the main window and came back to my iframe test site. Both window.frames["test2"].history.length and history.length still gave me the same count by increasing the length by 2. Did I do it wrong? Is there a way to track only the iframe history?

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  • error while converting the byte arry to image ,after modifying the byte array and the byte array is

    - by geehta
    Hi, this is my code. Here i hv formed the byte array of img, i am trying to add some vlue to this byte array say 10 and i'll take care that the value is not exceeding 255. later if i try to redraw the image via the following code i am getting error at this line... what can be the problem.. without modification if i try to draw the image it is coming but if i cahnge some value it is not drawing.. public Image btoi(byte[] bt) { ms = new MemoryStream(bt, 0, bt.Length); img = Image.FromStream (ms, true); // error at this line ms.Close(); return img; }

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