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  • Operators vs Functions in C/C++

    - by user356106
    Someone recently asked me the difference between a C++ standard operator (e.g. new,delete,sizeof) and function (e.g. tan,delete, malloc). By "standard" I mean those provided by default by the compiler suite, and not user defined. Below were the answers I gave, though neither seemed satisfactory. (1) An operator doesn't need any headers to be included to use it : E.g. you can have a call to new without including any headers. However, a function (say free() ) does need headers included, compulsorily. (2) An operator is defined as such (ie as a class operator) somewhere in the standard headers. A function isn't. Can you critique these answers and give me a better idea of the difference?

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  • LinqToSql Sub Entiity Multiple And Operators

    - by halit
    Hi I have an Array of Featureset Id , My Vehicles table has got sub table as FeatureSets I wrote Sql Query Like SELECT [t0].[ID] FROM [dbo].[SearchResultView] AS [t0] Join [dbo].[VehicleFeatureSet] AS [t1] on t0.ID = t1.VehicleID where t1.FeatureSetID = 1 and t1.FeatureSetID= 2 and t1.FeatureSetID= 3 I tried. But I Couldn't var features = Request.QueryString["FeatureSets"].Split(',').ToList().ConvertAll(new Converter<string, int>(StrinToint)); IQueryable<SearchResultView> result = db.SearchResultViews.Where(m => m.Active == true); foreach (var featuree in features) { result = result.Where(m => m.VehicleFeatureSets.Any(c => c.FeatureSetID == featuree)); } How Can I write this LINQ Query

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  • Evaluation of (de)reference operators

    - by Micha
    I have an (uncommented...) source file which I'm trying to understand. static const Map *gCurMap; static std::vector<Map> mapVec; then auto e = mapVec.end(); auto i = mapVec.begin(); while(i!=e) { // ... const Map *map = gCurMap = &(*(i++)); // ... } I don't understand what &(*(i++)) does. It does not compile when just using i++, but to me it looks the same, because I'm "incrementing" i, then I'm requesting the value at the given address and then I'm requesting the address of this value?!

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  • Identity operators in Swift

    - by Tao
    If a is identical to c, b is identical to c, why a is not identical to b? var a = [1, 2, 3] var b = a var c = a[0...2] a === c // true b === c // true a === b // false If a, b, c are constants: let a = [1, 2, 3] let b = a let c = a[0...2] a === c // true b === c // true a === b // true

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  • Using enum values to represent binary operators (or functions)

    - by Bears will eat you
    I'm looking for an elegant way to use values in a Java enum to represent operations or functions. My guess is, since this is Java, there just isn't going to be a nice way to do it, but here goes anyway. My enum looks something like this: public enum Operator { LT, LTEQ, EQEQ, GT, GTEQ, NEQ; ... } where LT means < (less than), LTEQ means <= (less than or equal to), etc - you get the idea. Now I want to actually use these enum values to apply an operator. I know I could do this just using a whole bunch of if-statements, but that's the ugly, OO way, e.g.: int a = ..., b = ...; Operator foo = ...; // one of the enum values if (foo == Operator.LT) { return a < b; } else if (foo == Operator.LTEQ) { return a <= b; } else if ... // etc What I'd like to be able to do is cut out this structure and use some sort of first-class function or even polymorphism, but I'm not really sure how. Something like: int a = ..., b = ...; Operator foo = ...; return foo.apply(a, b); or even int a = ..., b = ...; Operator foo = ...; return a foo.convertToOperator() b; But as far as I've seen, I don't think it's possible to return an operator or function (at least, not without using some 3rd-party library). Any suggestions?

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  • DWORD to bytes using bitwise shift operators

    - by Dave18
    I can't get it to work correctly. #include <windows.h> int main() { DWORD i = 6521; BYTE first = i >> 32; BYTE second = i >> 24; BYTE third = i >> 16; BYTE fourth = i >> 8; i = (((DWORD)fourth) << 24) | (((DWORD)third) << 16) | (((DWORD)second) << 8) | first; }

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  • Turning logical expression around

    - by BluePrint
    I have the following code: bool s = true; for (...; ...; ...) { // code that defines A, B, C, D // and w, x, y, z if (!(A < w) && s == true) { s = false; } if (!(B < x) && s == true) { s = false; } if (!(C < y) && s == true) { s = false; } if (!(D < z) && s == true) { s = false; } } This code is working well. However, I want to, for several (unimportant) reasons, change the code so that I can initiate s = false; and set it to true inside the if-statement. It tried the following: bool s = false; for (...; ...; ...) { // code that defines A, B, C, D // and w, x, y, z if (A >= w && s == false) { s = true; } if (B >= x && s == false) { s = true; } if (C >= y && s == false) { s = true; } if (D >= z && s == false) { s = true; } } However, this is not working properly as the code above is working. I know thought wrong somewhere in the logic, but I can't figure out where. Does anbyone see my probably obvious error? EDIT: Added three more if-statemets. Missed them since they were commented away.

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  • Ternary operators in C#

    - by pm_2
    With the ternary operator, it is possible to do something like the following (assuming Func1() and Func2() return an int: int x = (x == y) ? Func1() : Func2(); However, is there any way to do the same thing, without returning a value? For example, something like (assuming Func1() and Func2() return void): (x == y) ? Func1() : Func2(); I realise this could be accomplished using an if statement, I just wondered if there was a way to do it like this.

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  • SQL - logical AND among multiple rows

    - by potrnd
    Hello, First of all sorry that I could not think of a more descriptive title. What I want to do is the following using only SQL: I have some lists of strings, list1, list2 and list3. I have a dataset that contains two interesting columns, A and B. Column A contains a TransactionID and column B contains an ItemID. Naturally, there can be multiple rows that share the same TransactionIDs. I need to catch those transactions that have at least one item ID that exists whithin each list (list1, list2 AND list3). I also need to count how many times does that happen for each transaction. I hope that makes enough sense, perhaps I will be able to explain it better with a clear head. Thanks in advance

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  • Is It Possible To Recover A Partial LVM Logical Volume?

    - by Terry Wang
    Background It is an Ubuntu 12.04 VirtualBox VM with 5 virtual HDDs (VDI), NOTE this is just a test VM, so not well planned ahead: ubuntu.vdi for / (/dev/mapper/ubuntu-root AKA /dev/ubuntu/root) and /home (/dev/mapper/ubuntu-home) weblogic.vdi - /dev/sdb (mounted on /bea for weblogic and other stuff) btrfs1.vdi - /dev/sdc (part of btrfs -m raid1 -d raid1 configuration) btrfs2.vdi - /dev/sdd (part of btrfs -m raid1 -d raid1 configuration) more.vdi - /dev/sde (added this virtual HDD because / ran out of inodes and it wasn't easy to figure out what to delete so as to free up inodes, so I just added the new virtual HDD, created PV, added it to existing volume group ubuntu, grew the root logical volume to work around the inode issue -_-) What happened? Last Friday, before finishing up I wanted to free up some disk space on that box, for some reason I thought the more.vdi was useless and tried to detach it from the VM, I then clicked delete (should have clicked keep files damn!) by mistake when detaching. Unfortunately I didn't have backup for it. All too late. What I have tried Tried to undelete (use testdisk and photorec) the vdi files but it takes too long and recovered heaps of .vdi files that I didn't want (huge, filled the disk, damn!). I finally gave up. Fortunately most of data is on separate ext4 partition and btrfs volumes. Out of curiosity, I still tried to mount the logical volumes and see if it is possible to at least recover the /var and /etc I tried to use system rescue cd to boot and activate the volume groups, I got: Couldn't find device with uuid xxxx. Refusing activation of the partial LV root. Use --partial to override. 1 logical volume(s) in volume group "ubuntu" now active. I was able to mount home LV but not root LV. I am wondering if it is possible to access the root LV any more. Under the bonnet, data (on LV root - /) was striped to more.vdi (PV), I know it's almost impossible to to recover. But I am still curious about how system administrator/DevOps guys deal with this sort of situation;-) Thanks in advance.

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  • What is logical cohesion, and why is it bad or undesirable?

    - by Matt Fenwick
    From the c2wiki page on coupling & cohesion: Cohesion (interdependency within module) strength/level names : (from worse to better, high cohesion is good) Coincidental Cohesion : (Worst) Module elements are unrelated Logical Cohesion : Elements perform similar activities as selected from outside module, i.e. by a flag that selects operation to perform (see also CommandObject). i.e. body of function is one huge if-else/switch on operation flag Temporal Cohesion : operations related only by general time performed (i.e. initialization() or FatalErrorShutdown?()) Procedural Cohesion : Elements involved in different but sequential activities, each on different data (usually could be trivially split into multiple modules along linear sequence boundaries) Communicational Cohesion : unrelated operations except need same data or input Sequential Cohesion : operations on same data in significant order; output from one function is input to next (pipeline) Informational Cohesion: a module performs a number of actions, each with its own entry point, with independent code for each action, all performed on the same data structure. Essentially an implementation of an abstract data type. i.e. define structure of sales_region_table and its operators: init_table(), update_table(), print_table() Functional Cohesion : all elements contribute to a single, well-defined task, i.e. a function that performs exactly one operation get_engine_temperature(), add_sales_tax() (emphasis mine). I don't fully understand the definition of logical cohesion. My questions are: what is logical cohesion? Why does it get such a bad rap (2nd worst kind of cohesion)?

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  • how to refer to the current struct in an overloaded operator?

    - by genesys
    Hi! I have a struct for which i want to define a relative order by defining < , , <= and = operators. actually in my order there won't be any equality, so if one struct is not smaller than another, it's automatically larger. I defined the first operator like this: struct MyStruct{ ... ... bool operator < (const MyStruct &b) const {return (somefancycomputation);} }; now i'd like to define the other operators based on this operator, such that <= will return the same as < and the other two will simply return the oposite. so for example for the operator i'd like to write something like bool operator > (const MyStruct &b) const {return !(self<b);} but i don't know how to refere to this 'self' since i can refere only to the fields inside the current struct. whole is in C++ hope my question was understandable :) thank you for the help!

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  • Putting indexes in separate filegroup kills our queries

    - by womp
    Can anyone shed some light on this? On our dev boxes, our database resides entirely in the PRIMARY filegroup, and everything works fine. On one of our production servers, recently upgraded from 2005 to 2008, we noticed it was performing slower than it should. On this machine, there are two filegroups - PRIMARY and INDEXES. Both filegroups contain 1 file per logical volume, one logical volume per CPU, (and each logical volume is a RAID 10 of 4 physical disks). We isolated a few queries that were performing fast on the dev boxes and slow (up to 40x slower) on the production machine. Turned out these queries were using the non-clustered indexes that resided in the INDEXES filegroup. Tweaking some of the queries to only use clustered indexes that were in the PRIMARY filegroup dropped their times back to normal. As a final confirmation, we redeployed the same database on the same machine to have everything in PRIMARY, and things went back to normal! Here's the statistics output of one of the queries, run identically on the machine with different filegroup configurations (table names changed to protect the innocent): FAST (everything in PRIMARY filegroup): (3 row(s) affected) Table '0'. Scan count 2, logical reads 14, ... Table '1'. Scan count 0, logical reads 0, ... Table '1'. Scan count 0, logical reads 0, ... Table '2'. Scan count 2, logical reads 7, ... Table '3'. Scan count 2, logical reads 1012, ... Table '4'. Scan count 1, logical reads 3, ... SQL Server Execution Times: CPU time = 437 ms, elapsed time = 445 ms. SLOW (indexes split into their own filegroup): (3 row(s) affected) Table '0'. Scan count 209, logical reads 428, ... Table '1'. Scan count 0, logical reads 0,... Table '2'. Scan count 1021, logical reads 9043,.... Table '3'. Scan count 209, logical reads 105754, .... Table '4'. Scan count 0, logical reads 0, .... Table '5'. Scan count 1, logical reads 695, ... **Table '#46DA8CA9'. Scan count 205, logical reads 205, ...** Table '6'. Scan count 6, logical reads 436, ... Table '7'. Scan count 1, logical reads 12,.... SQL Server Execution Times: CPU time = 17581 ms, elapsed time = 17595 ms. Notice the weird temp table and extra tables involved in the slow query. It seems clear that having a second file group is making SQL Server batty with choosing an execution plan. What the heck is going on?

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  • Change the logical name of sql server express 2005 database file?

    - by oob
    In Microsoft SQL Server Management Studio Express for Sql Server Express 2005, I needed to copy a database for testing and keep it on the same server as the old database. I did the following: Right Click on Databases Created new database Detached the database I wanted to copy "Restored" my new database from the backup file of my old database. I did this by clicking the 'Overwrite the existing database' box on the Options pane, and I changed the paths in the 'restore as' options so that they pointed to my new .mdf and .ldf files. Everything is working like I want. Problem is, when I right-click - Properties - Files on my new database, the logical name of the .mdf file is the same as the logical name of the old .mdf file. They are actually different files - they just share the same logical name? I guess maybe this isn't a short-term problem, but I can see it confusing somebody down the road. Any way to change the logical name of the .mdf file? UPDATE EDIT - Apparently you can just change the logical name through the GUI by, get this, clicking on it and typing a new name. I could swear that was not possible when I posted this, but maybe it was and I somehow missed it! Either way - the solution below should still work but doing it through the GUI is also an option.

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  • Java operator precedence guidelines

    - by trashgod
    Misunderstanding Java operator precedence is a source of frequently asked questions and subtle errors. I was intrigued to learn that even the Java Language Specification says, "It is recommended that code not rely crucially on this specification." JLS §15.7 Preferring clear to clever, are there any useful guidelines in this area? Here are a number of resources on the topic: JLS Operators JLS Precedence Java Glossary Princeton Sun Tutorial University of West Florida Usenet discussion Additions or corrections welcome.

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  • How to use ternary operator instead of if-else in PHP

    - by Mac Taylor
    hey guys i need to shorten or better to say ., harden my codes this is my original code : if ($type = "recent") { $OrderType = "sid DESC"; }elseif ($type = "pop"){ $OrderType = "counter DESC"; }else { $OrderType = "RAND()"; } now how can i use markers like this : $OrderType = ($type = "recent") ? "sid DESC" : "counter DESC" ; i tried but i didnt know how to write elseif in operators

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  • Perl ||= operator for PHP and Javascript

    - by zaf
    Just been re-introduced to the Perl '||=' operator from the classic Orcish Maneuver example: keys my %or_cache = @in; @out = sort { ($or_cache{$a} ||= KEY($a)) cmp ($or_cache{$b} ||= KEY($b)) } @in; Is this operator available in PHP and Javascript? And if not, do these two languages allow user defined operators?

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  • 'AND' vs '&&' as operator

    - by ts
    Actually, i am facing a codebase where developpers decided to use 'AND' and 'OR' instead of '&&' and '||'. I know that there is difference in operators precedence (&& goes before 'and'), but with given framework (prestashop to be precise) is clearly not a reason. So, my question: which version are you using? Is 'and' more readable than '&&'? || there is ~ difference?

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  • In what situation should the built-in 'operator' module be used in python?

    - by apphacker
    I'm speaking of this module: http://docs.python.org/library/operator.html From the article: The operator module exports a set of functions implemented in C corresponding to the intrinsic operators of Python. For example, operator.add(x, y) is equivalent to the expression x+y. The function names are those used for special class methods; variants without leading and trailing __ are also provided for convenience. I'm not sure I understand the benefit or purpose of this module.

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  • Are +=, |=, &= etc atomic?

    - by SF.
    Are the "modify" operators like +=, |=, &= etc atomic? I know ++ is atomic (if you perform x++; in two different threads "simultaneously", you will always end up with x increased by 2, as opposed to x=x+1 with optimization switched off.) What I wonder is whether variable |= constant, and the likes are thread-safe or do I have to protect them with a mutex? (...or is it CPU-dependent? In this case, how is it on ARM?)

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