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• implementing keepalives with Java

  - by Bilal

  Hi All, I am biulding a client-server application where I have to implement a keepalive mechanism in order to detect that the client has crashed or not. I have separate threads on both client and server side. the client thread sends a "ping" then sleeps for 3 seconds, while the server reads the BufferedInput Stream and checks whether ping is received, if so it makes the ping counter eqauls zero, else it increments the counter by +1, the server thread then sleeps for 3 seconds, if the ping counter reaches 3, it daclares the client as dead. The problem is that when the server reads the input stream, its a blocking call, and it blocks untill the next ping is received, irrespective of how delayed it is, so the server never detects a missed ping. any suggestions, so that I can read the current value of the stream and it doesn't block if there is nothing on the incoming stream. Thanks,

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• Computation overhead in C# - Using getters/setters vs. modifying arrays directly and casting speeds

  - by Jeffrey Kern

  I was going to write a long-winded post, but I'll boil it down here: I'm trying to emulate the graphical old-school style of the NES via XNA. However, my FPS is SLOW, trying to modify 65K pixels per frame. If I just loop through all 65K pixels and set them to some arbitrary color, I get 64FPS. The code I made to look-up what colors should be placed where, I get 1FPS. I think it is because of my object-orented code. Right now, I have things divided into about six classes, with getters/setters. I'm guessing that I'm at least calling 360K getters per frame, which I think is a lot of overhead. Each class contains either/and-or 1D or 2D arrays containing custom enumerations, int, Color, or Vector2D, bytes. What if I combined all of the classes into just one, and accessed the contents of each array directly? The code would look a mess, and ditch the concepts of object-oriented coding, but the speed might be much faster. I'm also not concerned about access violations, as any attempts to get/set the data in the arrays will done in blocks. E.g., all writing to arrays will take place before any data is accessed from them. As for casting, I stated that I'm using custom enumerations, int, Color, and Vector2D, bytes. Which data types are fastest to use and access in the .net Framework, XNA, XBox, C#? I think that constant casting might be a cause of slowdown here. Also, instead of using math to figure out which indexes data should be placed in, I've used precomputed lookup tables so I don't have to use constant multiplication, addition, subtraction, division per frame. :)

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• Masking a bit in C returning unexpected result

  - by Eamorr

  0x7F000000 is 0111 1111 0000 0000 0000 0000 0000 0000 in 32 bit binary. 0x01000058 is 0000 0001 0000 0000 0000 0000 0101 1000. When I AND the two numbers together I expect 0000 0001 0000 0000 0000 0000 0000 0000, but for some reason I get 0. Here is my code: #define MASK_binop 0x80000000 #define MASK_operation 0x7F000000 int instruction=atoi(line); if((MASK_binop & instruction)>0) printf("binop\n"); else if((MASK_operation & instruction)>0) printf("operation\n"); Each of the above comparisons keeps returning zero. Is it something to do with 32/64 bits? I'm using 64-bit compiler.

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• how can i substitute a NULL value for a 0 in an SQL Query result

  - by Name.IsNullOrEmpty

  SELECT EmployeeMaster.EmpNo, Sum(LeaveApplications.LeaveDaysTaken) AS LeaveDays FROM EmployeeMaster FULL OUTER JOIN LeaveApplications ON EmployeeMaster.id = LeaveApplications.EmployeeRecordID INNER JOIN LeaveMaster ON EmployeeMaster.id = LeaveMaster.EmpRecordID GRoup BY EmployeeMaster.EmpNo order by LeaveDays Desc with the above query, if an employee has no leave application record in table LeaveApplications, then their Sum(LeaveApplications.LeaveDaysTaken) AS LeaveDays column returns NULL. What i would like to do is place a value of 0 (Zero) instead of NULL. I want to do this because i have a calculated column in the same query whose formular depends on the LeaveDays returned and when LeaveDays is NULL, the formular some how fails. Is there away i can put 0 for NULL such that that i can get my desired result.

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• c++ floating point precision loss: 3015/0.00025298219406977296

  - by SigTerm

  The problem. Microsoft Visual C++ 2005 compiler, 32bit windows xp sp3, amd 64 x2 cpu. Code: double a = 3015.0; double b = 0.00025298219406977296; //*((unsigned __int64*)(&a)) == 0x40a78e0000000000 //*((unsigned __int64*)(&b)) == 0x3f30945640000000 double f = a/b;//3015/0.00025298219406977296; the result of calculation (i.e. "f") is 11917835.000000000 (*((unsigned __int64*)(&f)) == 0x4166bb4160000000) although it should be 11917834.814763514 (i.e. *((unsigned __int64*)(&f)) == 0x4166bb415a128aef). I.e. fractional part is lost. Unfortunately, I need fractional part to be correct. Questions: 1) Why does this happen? 2) How can I fix the problem? Additional info: 0) The result is taken directly from "watch" window (it wasn't printed, and I didn't forget to set printing precision). I also provided hex dump of floating point variable, so I'm absolutely sure about calculation result. 1) The disassembly of f = a/b is: fld qword ptr [a] fdiv qword ptr [b] fstp qword ptr [f] 2) f = 3015/0.00025298219406977296; yields correct result (f == 11917834.814763514 , *((unsigned __int64*)(&f)) == 0x4166bb415a128aef ), but it looks like in this case result is simply calculated during compile-time: fld qword ptr [__real@4166bb415a128aef (828EA0h)] fstp qword ptr [f] So, how can I fix this problem? P.S. I've found a temporary workaround (i need only fractional part of division, so I simply use f = fmod(a/b)/b at the moment), but I still would like to know how to fix this problem properly - double precision is supposed to be 16 decimal digits, so such calculation isn't supposed to cause problems.

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• How to use SQL trigger to record the affected column's row number

  - by Freeman

  I want to have an 'updateinfo' table in order to record every update/insert/delete operations on another table. In oracle I've written this: CREATE TABLE updateinfo ( rnumber NUMBER(10), tablename VARCHAR2(100 BYTE), action VARCHAR2(100 BYTE), UPDATE_DATE date ) DROP TRIGGER TRI_TABLE; CREATE OR REPLACE TRIGGER TRI_TABLE AFTER DELETE OR INSERT OR UPDATE ON demo REFERENCING NEW AS NEW OLD AS OLD FOR EACH ROW BEGIN if inserting then insert into updateinfo(rnumber,tablename,action,update_date ) values(rownum,'demo', 'insert',sysdate); elsif updating then insert into updateinfo(rnumber,tablename,action,update_date ) values(rownum,'demo', 'update',sysdate); elsif deleting then insert into updateinfo(rnumber,tablename,action,update_date ) values(rownum,'demo', 'delete',sysdate); end if; -- EXCEPTION -- WHEN OTHERS THEN -- Consider logging the error and then re-raise -- RAISE; END TRI_TABLE; but when checking updateinfo, all rnumber column is zero. is there anyway to retrieve the correct row number?

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• Detecting coincident subset of two coincident line segments

  - by Jared Updike

  This question is related to: How do I determine the intersection point of two lines in GDI+? (great explanation of algebra but no code) How do you detect where two line segments intersect? (accepted answer doesn't actually work) But note that an interesting sub-problem is completely glossed over in most solutions which just return null for the coincident case even though there are three sub-cases: coincident but do not overlap touching just points and coincident overlap/coincident line sub-segment For example we could design a C# function like this: public static PointF[] Intersection(PointF a1, PointF a2, PointF b1, PointF b2) where (a1,a2) is one line segment and (b1,b2) is another. This function would need to cover all the weird cases that most implementations or explanations gloss over. In order to account for the weirdness of coincident lines, the function could return an array of PointF's: zero result points (or null) if the lines are parallel or do not intersect (infinite lines intersect but line segments are disjoint, or lines are parallel) one result point (containing the intersection location) if they do intersect or if they are coincident at one point two result points (for the overlapping part of the line segments) if the two lines are coincident

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• DBD::CSV: Problem with userdefined functions

  - by sid_com

  From the SQL::Statement::Functions documentation: Creating User-Defined Functions ... More complex functions can make use of a number of arguments always passed to functions automatically. Functions always receive these values in @_: sub FOO { my( $self, $sth, $rowhash, @params ); } #!/usr/bin/env perl use 5.012; use warnings; use strict; use DBI; my $dbh = DBI->connect( "DBI:CSV:", undef, undef, { RaiseError => 1, } ); my $table = 'wages'; my $array_ref = [ [ 'id', 'number' ], [ 0, 6900 ], [ 1, 3200 ], [ 2, 1800 ], ]; $dbh->do( "CREATE TEMP TABLE $table AS import( ? )", {}, $array_ref ); sub routine { my $self = shift; my $sth = shift; my $rowhash = shift; # return $_[0] / 30; }; $dbh->do( "CREATE FUNCTION routine" ); my $sth = $dbh->prepare( "SELECT id, routine( number ) AS result FROM $table" ); $sth->execute(); $sth->dump_results(); When I try this I get an error-message: DBD::CSV::st execute failed: Use of uninitialized value $_[0] in division (/) at ./so.pl line 27. [for Statement "SELECT id, routine( number ) AS result FROM "wages""] at ./so.pl line 34. When I comment out the third argument I works as expected ( because it looks as if the third argument is missing ): #!/usr/bin/env perl ... sub routine { my $self = shift; my $sth = shift; #my $rowhash = shift; return $_[0] / 30; }; ... 0, 230 1, 106.667 2, 60 3 rows Is this a bug?

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• Converting Byte[] to String - Interbase to C# - InvalidCastException

  - by NorthernOutpost

  I'm using OleDbDataReader rdr to read a "Comments" field in BLOB form (sub_type 1 segment size 80) into a string from an Interbase DB, and I keep getting exceptions. Any suggestions? Attempt #1 ls_Chap_Comments.Add((rdr["Comments"]).ToString()); InvalidCastException: The data value could not be converted for reasons other than sign mismatch or data overflow. For example, the data was corrupted in the data store but the row was still retrievable." Attempt #2 byte[] b = new byte[100]; b = (byte[])rdr["Comments"]; string s = System.Text.ASCIIEncoding.ASCII.GetString(b); InvalidCastException: Unable to cast object of type System.String to type System.Byte[] Attempt #3 // 17 is the BLOB column zero-based location for "Comments" retval = rdr.GetBytes(17, startIndex, outbyte, 0, bufferSize); InvalidCastException: Unable to cast object of type System.String to type System.Byte[]. Any suggestions would be really appreciated!

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• Right design to validate attributes of a class instance

  - by systempuntoout

  Having a simple Python class like this: class Spam(object): __init__(self, description, value): self.description = description self.value = value Which is the correct approach to check these constraints: "description cannot be empty" "value must be greater than zero" Should i: 1.validate data before creating spam object ? 2.check data on __init__ method ? 3.create an is_valid method on Spam class and call it with spam.isValid() ? 4.create an is_valid static method on Spam class and call it with Spam.isValid(description, value) ? 5.check data on setters? 6.... Could you recommend a well designed\Pythonic\not verbose (on class with many attributes)\elegant approach?

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• MySQL: Select pages that are not tagged?

  - by lauthiamkok

  Hi, I have a db with two tables like these below, page table pg_id title 1 a 2 b 3 c 4 d tagged table tagged_id pg_id 1 1 2 4 I want to select the pages which are tagged, I tried with this query below but doesn't work, SELECT * FROM root_pages LEFT JOIN root_tagged ON ( root_tagged.pg_id = root_pages.pg_id ) WHERE root_pages.pg_id != root_tagged.pg_id It returns zero - Showing rows 0 - 1 (2 total, Query took 0.0021 sec) But I want it to return pg_id title 2 b 3 c My query must have been wrong?? How can I return the pages which are not tagged correctly? Thanks.

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• C/C++ memory usage API in Linux/Windows

  - by minjang

  I'd like to obtain memory usage information for both per process and system wide. In Windows, it's pretty easy. GetProcessMemoryInfo and GlobalMemoryStatusEx do these jobs greatly and very easily. For example, GetProcessMemoryInfo gives "PeakWorkingSetSize" of the given process. GlobalMemoryStatusEx returns system wide available memory. However, I need to do it on Linux. I'm trying to find Linux system APIs that are equivalent GetProcessMemoryInfo and GlobalMemoryStatusEx. I found 'getrusage'. However, max 'ru_maxrss' (resident set size) in struct rusage is just zero, which is not implemented. Also, I have no idea to get system-wide free memory. Current workaround for it, I'm using "system("ps -p %my_pid -o vsz,rsz");". Manually logging to the file. But, it's dirty and not convenient to process the data. I'd like to know some fancy Linux APIs for this purpose.

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• Lazy sequence or recur for mathematical power function?

  - by StackedCrooked

  As an exercise I implemented the mathematical power function. Once using recur: (defn power [a n] (let [multiply (fn [x factor i] (if (zero? i) x (recur (* x factor) factor (dec i))))] (multiply a a (dec n)))) And once with lazy-seq: (defn power [a n] (letfn [(multiply [a factor] (lazy-seq (cons a (multiply (* a factor) factor))))] (nth (multiply a a) (dec n)))) Which implementation do you think is superior? I truly have no idea.. (I'd use recur because it's easier to understand.) I read that lazy-seq is fast because is uses internal caching. But I don't see any opportunities for caching in my sample. Am I overlooking something?

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• Length of an HTMLObjectCollection is incorrect in Internet Explorer

  - by Mayank Gupta

  I have three cells in different rows in a table having same name.e.g. <td name = "x"> is present in 3 different rows. I am using document.getElementsByName() to obtain a collection of these cells and trying to calculate the length of this collection. e.g. var obj = doucment.getElementsByName("X"); var length = obj.length; This code works fine in Google Chrome but in IE the length is return as 0(zero). Can anyone tell me how to sove this problem in IE?

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• Credit Card checksums and validations that do not require connection to the financial institution

  - by cjavapro

  The validations I know of are: Checksum the whole card number should add up to zero. (range is 0-9) Check the first digit(s) against the card type Check the length against the card type Check the CCV length against the card type (I think all the major types are 3 anyway) Of course make sure it is accepted card type as well as non expired. Are there any other validations :) (I expect many folks did not know about all of these) The reason I ask is because I overheard there was one to checksum number against expiration or CCV.. I just wanted to check.

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• How to use a value from one stored procedure in another?

  - by RoguePlanetoid

  I have the following statement in a Stored Procedure: DECLARE @Count INT EXEC @Count = GetItemCount 123 SELECT @Count Which calls another stored procedure with the following statement inside: SELECT COUNT(Item) FROM tblItem WHERE ID = @ID However when I test the call the EXEC outputs the value correctly but it is not assigned to the @Count Variable correctly. I've seen examples or stored procedures used like this, including here but none had a parameter and a return value used (that I could find). The ID Parameter is passed into the second statement which returns a count value used by the first StoredProcedure - all the info I have read seems to indicate this should work - but it doesn't the @Count value is aways zero, even when the GetItemCount returns always the correct value. This is in Microsoft SQL Server 2008 if that helps.

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• imap_open dies when being called

  - by blauwblaatje

  Hi, I've got the following code: The script dies. I get zero responds, nothing from apache, no "foo" or "bar", nothing. I can however connect to the imap server (nc localhost ...), I can also put the script on another server and connect to the same imap server. So, I think there's something wrong with the php on this server. But I can't figure out what I'm missing, forgetting or didn't install. phpinfo() tells me php is configured --with-imap and --with-imap-ssl. The OS is CentOS, btw.

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• GetDiskFreeSpaceEx in winCE 5.0 emulator?

  - by vidhyarthi

  Hi, I am trying to use GetDiskFreeSpaceEx in wince5.0 emulator. This is the following code I have written. ULARGE_INTEGER notused, totalBytes, freeBytes; GetDiskFreeSpaceEx(_T("\\Windows"),&notused,&totalBytes,&freeBytes); printf(" Error in disk %d ", GetLastError()); printf(" values = notused %d,totalBytes %d,freeBytes %d",notused,totalBytes,freeBytes); *Output * 14540 PID:3db620e TID:3e5c83e Error in disk 0 14540 PID:3db620e TID:3e5c83e values = notused 25987296,totalBytes 0,freeBytes 26234880 The total bytes that I get is zero. Am I missing something or in emulator is that OK?

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• Problems with variadic macros in C

  - by imikedaman

  Hi, I'm having a problem with optional arguments in #define statements in C, or more specifically with gcc 4.2: bool func1(bool tmp) { return false; } void func2(bool tmp, bool tmp2) {} #define CALL(func, tmp, ...) func(tmp, ##__VA_ARGS__) int main() { // this compiles CALL(func2, CALL(func1, false), false); // this fails with: Implicit declaration of function 'CALL' CALL(func2, false, CALL(func1, false)); } That's obviously a contrived example, but does show the problem. Does anyone know how I can get the optional arguments to "resolve" correctly? Additional information: If I remove the ## before _VA_ARGS_, and do something like this: bool func2(bool tmp, bool tmp2) { return false; } #define CALL(func, tmp, ...) func(tmp, __VA_ARGS__) int main() { CALL(func2, false, CALL(func2, false, false)); } That compiles, but it no longer works with zero arguments since it would resolve to func(tmp, )

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• Is there a standardized (Meta?) Tag for the Date of a Website?

  - by Michael Stum

  One thing that search engines really suck with is the date when a website was created. You know the problem: You search for some CSS or JavaScript problem and Google returns a ton of results from 2002 explaining how to fix the problem in IE 5.5 and Netscape 4.6 while the helpful articles are buried on Page 3. There is only one use for Page 3, and meaningful search results are not it. Anyway, I just wonder if there is a standardized or at least generally accepted tag or meta tag that I can put on my own pages to indicate the date they were created? Not that it helps filtering out the old crap out of search results (especially since the people at #1 with their 2002 articles have zero incentive to change), but I'd just like to do my part :P

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• Simple, Custom Parsing with c++

  - by bradkovach

  Hi! I have been reading SO for some time now, but I truly cannot find any help for my problem. I have a c++ assignment to create an IAS simulator. Here is some sample code... 0 1 a 1 2 b 2 c 3 1 10 begin 11 . load a, subtract b and offset by -1 for jump+ 11 load M(0) 12 sub M(1) 13 sub M(3) 14 halt Using c++, I need to be able to read these lines and store them in a "memory register" class that I already have constructed... For example, the first line would need to store "1 a" in register zero. How can I parse out the number at the line beginning and then store the rest as a string? I have setup storage using a class that is called using mem.set(int, string);. int is the memory location at the beginning of the line and string is the stored instruction.

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• Can you call compiled JRuby classes from java?

  - by John Baker

  So I came up with the general idea to write some code in JRuby, then access all the classes via Java. I have no idea if this is at all possible but I wanted to ask anyway. Lets say I have some JRuby code: class adder def addme return 22 end end If I compiled this with jrubyc is there any way I could then possibly do something like this in java: import adder; class anything { void testMethod() { adder a = new adder(); int x = a.addme(); } } After looking at it now it sort of makes me think that Java will have zero idea what sort of item test addme is going to return so that might not work. I don't know but I wanted to throw it out there anyway. Thanks

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• C++ deleting a pointer

  - by eSKay

  On this page, its written that One reason is that the operand of delete need not be an lvalue. Consider: delete p+1; delete f(x); Here, the implementation of delete does not have a pointer to which it can assign zero. Adding a number to a pointer shifts it forward in memory by those many number of sizeof(*p) units. So, what is the difference between delete p and delete p+1, and why would making the pointer 0 only be a problem with delete p+1?

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• F# operator over-loading question

  - by jyoung

  The following code fails in 'Evaluate' with: "This expression was expected to have type Complex but here has type double list" Am I breaking some rule on operator over-loading on '(+)'? Things are OK if I change '(+)' to 'Add'. open Microsoft.FSharp.Math /// real power series [kn; ...; k0] => kn*S^n + ... + k0*S^0 type Powers = double List let (+) (ls:Powers) (rs:Powers) = let rec AddReversed (ls:Powers) (rs:Powers) = match ( ls, rs ) with | ( l::ltail, r::rtail ) -> ( l + r ) :: AddReversed ltail rtail | ([], _) -> rs | (_, []) -> ls ( AddReversed ( ls |> List.rev ) ( rs |> List.rev) ) |> List.rev let Evaluate (ks:Powers) ( value:Complex ) = ks |> List.fold (fun (acc:Complex) (k:double)-> acc * value + Complex.Create(k, 0.0) ) Complex.Zero

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• Python 3: Recursivley find if number is even

  - by pythonhack

  I am writing a program that must find if a number is even or not. It needs to follow this template. I can get it to find if a number is even or not recursively (call function and subtract 2, base case zero), but I am having a hard time following this template, based on how the isEven function is called in the main function. Any help would be greatly appreciated. Write a recursive function called isEven that finds whether a number is even or not: def isEven() #recursivley determine whether number is even or not def main(): number=int(input(“Enter a number : “)) if (isEven(number)): print(“Number is even”) else: print(“Number is not even”) main() Thank you! Appreciate it.

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