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  • "Whole-team" C++ features?

    - by Blaisorblade
    In C++, features like exceptions impact your whole program: you can either disable them in your whole program, or you need to deal with them throughout your code. As a famous article on C++ Report puts it: Counter-intuitively, the hard part of coding exceptions is not the explicit throws and catches. The really hard part of using exceptions is to write all the intervening code in such a way that an arbitrary exception can propagate from its throw site to its handler, arriving safely and without damaging other parts of the program along the way. Since even new throws exceptions, every function needs to provide basic exception safety — unless it only calls functions which guarantee throwing no exception — unless you disable exceptions altogether in your whole project. Hence, exceptions are a "whole-program" or "whole-team" feature, since they must be understood by everybody in a team using them. But not all C++ features are like that, as far as I know. A possible example is that if I don't get templates but I do not use them, I will still be able to write correct C++ — or will I not?. I can even call sort on an array of integers and enjoy its amazing speed advantage wrt. C's qsort (because no function pointer is called), without risking bugs — or not? It seems templates are not "whole-team". Are there other C++ features which impact code not directly using them, and are hence "whole-team"? I am especially interested in features not present in C. Update: I'm especially looking for features where there's no language-enforced sign you need to be aware of them. The first answer I got mentioned const-correctness, which is also whole-team, hence everybody needs to learn about it; however, AFAICS it will impact you only if you call a function which is marked const, and the compiler will prevent you from calling it on non-const objects, so you get something to google for. With exceptions, you don't even get that; moreover, they're always used as soon as you use new, hence exceptions are more "insidious". Since I can't phrase this as objectively, though, I will appreciate any whole-team feature. Appendix: Why this question is objective (if you wonder) C++ is a complex language, so many projects or coding guides try to select "simple" C++ features, and many people try to include or exclude some ones according to mostly subjective criteria. Questions about that get rightfully closed regularly here on SO. Above, instead, I defined (as precisely as possible) what a "whole-team" language feature is, provide an example (exceptions), together with extensive supporting evidence in the literature about C++, and ask for whole-team features in C++ beyond exceptions. Whether you should use "whole-team" features, or whether that's a relevant concept, might be subjective — but that only means the importance of this question is subjective, like always.

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  • Zelda-style top-down RPG. How to store tile and collision data?

    - by Delerat
    I'm looking to build a Zelda: LTTP style top-down RPG. I've read a lot on the subject and am currently going back and forth on a few solutions. I'm using C#, MonoGame, and Tiled. For my tile maps, these are the choices I can see in front of me: Store each tile as its own array. Each one having 3-4 layers, texture/animation, depth, flags, and maybe collision(depending on how I do it). I've read warning about memory issues going this route, and my biggest map will probably be 160x120 tiles. My average map however will be about 40x30. The number of tiles might cut in half if I decide to double my tile size, which is currently 16x16. This is the most appealing approach for me, as I feel like I would know how to save maps, make changes, and separate it into chunks for collision checks. Store the static parts of my tile map in multiple arrays acting as the different layers. Then I would just use entities for anything that wasn't static. All of the other tile data such as collisions, depth, etc., would be stored in their own layers as well I guess? This way just seems messy to me though. Regardless of which one I choose, I'm also unsure how to plan all of that other tile data. I could write a bunch of code that would know which integer represents what tile and it's data, but if I changed a tileset in Tiled and exported it again, all of those integers could potentially change and I'd have to adjust a whole bunch of code. My other issue is about how I could do collision. I want to at least support angled collision that slides you around the corners of objects like LTTP does, if not more oddball shapes as well. So do I: Store collision as a flag for binary collision. Could I get this to support angles? Would it be fine to store collision as an integer and have each number represent a certain angle of collision? Store a list of rectangles or other shapes and do collision that way? Sorry for the large two-part(three-part?) question. I felt like these needed to be asked together as I believe each choice influences the other.

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  • RabbitMQ message consumers stop consuming messages

    - by Bruno Thomas
    Hi server fault, Our team is in a spike sprint to choose between ActiveMQ or RabbitMQ. We made 2 little producer/consumer spikes sending an object message with an array of 16 strings, a timestamp, and 2 integers. The spikes are ok on our devs machines (messages are well consumed). Then came the benchs. We first noticed that somtimes, on our machines, when we were sending a lot of messages the consumer was sometimes hanging. It was there, but the messsages were accumulating in the queue. When we went on the bench plateform : cluster of 2 rabbitmq machines 4 cores/3.2Ghz, 4Gb RAM, load balanced by a VIP one to 6 consumers running on the rabbitmq machines, saving the messages in a mysql DB (same type of machine for the DB) 12 producers running on 12 AS machines (tomcat), attacked with jmeter running on another machine. The load is about 600 to 700 http request per second, on the servlets that produces the same load of RabbitMQ messages. We noticed that sometimes, consumers hang (well, they are not blocked, but they dont consume messages anymore). We can see that because each consumer save around 100 msg/sec in database, so when one is stopping consumming, the overall messages saved per seconds in DB fall down with the same ratio (if let say 3 consumers stop, we fall around 600 msg/sec to 300 msg/sec). During that time, the producers are ok, and still produce at the jmeter rate (around 600 msg/sec). The messages are in the queues and taken by the consumers still "alive". We load all the servlets with the producers first, then launch all the consumers one by one, checking if the connexions are ok, then run jmeter. We are sending messages to one direct exchange. All consumers are listening to one persistent queue bounded to the exchange. That point is major for our choice. Have you seen this with rabbitmq, do you have an idea of what is going on ? Thank you for your answers.

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  • Doing arithmetic and passing it to the next command

    - by neurolysis
    I know how to do this in /bin/sh, but I'm struggling a bit in Windows. I know you can do arithmetic on 32-bit signed integers with SET /a 2+2 4 But how do I pass this to the next command? For example, the process I want to perform is as follows. Consumer editions of Windows have no native automated sleep function (I believe?) -- the best way to perform a sleep is to use PING in association with the -n switch to get that many seconds, minus one, of sleep. The following command is effective for a silent sleep: PING localhost -n 3 > NUL But I want to alias this into a sleep command. I'd like to have it elegant so that you enter the actual number of seconds you want to sleep after the command, right now I can do DOSKEY SLEEP=PING 127.0.0.1 -n $1 > NUL Which works, but it's always 1 second less than your input, so if you wanted to sleep for one second you would have to use the command SLEEP 2. That's not exactly ideal. Is there some way for me to pass the arithmetic of $1+1 and pass it on to the next command in Windows? I assume there is some way of using STDOUT...

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  • Criticize my code, please

    - by Micky
    Hey, I was applying for a position, and they asked me to complete a coding problem for them. I did so and submitted it, but I later found out I was rejected from the position. Anyways, I have an eclectic programming background so I'm not sure if my code is grossly wrong or if I just didn't have the best solution out there. I would like to post my code and get some feedback about it. Before I do, here's a description of a problem: You are given a sorted array of integers, say, {1, 2, 4, 4, 5, 8, 9, 9, 9, 9, 9, 9, 10, 10, 10, 11, 13 }. Now you are supposed to write a program (in C or C++, but I chose C) that prompts the user for an element to search for. The program will then search for the element. If it is found, then it should return the first index the entry was found at and the number of instances of that element. If the element is not found, then it should return "not found" or something similar. Here's a simple run of it (with the array I just put up): Enter a number to search for: 4 4 was found at index 2. There are 2 instances for 4 in the array. Enter a number to search for: -4. -4 is not in the array. They made a comment that my code should scale well with large arrays (so I wrote up a binary search). Anyways, my code basically runs as follows: Prompts user for input. Then it checks if it is within bounds (bigger than a[0] in the array and smaller than the largest element of the array). If so, then I perform a binary search. If the element is found, then I wrote two while loops. One while loop will count to the left of the element found, and the second while loop will count to the right of the element found. The loops terminate when the adjacent elements do not match with the desired value. EX: 4, 4, 4, 4, 4 The bold 4 is the value the binary search landed on. One loop will check to the left of it, and another loop will check to the right of it. Their sum will be the total number of instances of the the number four. Anyways, I don't know if there are any advanced techniques that I am missing or if I just don't have the CS background and made a big error. Any constructive critiques would be appreciated! #include <stdio.h> #include <stdlib.h> #include <string.h> #include <stddef.h> /* function prototype */ int get_num_of_ints( const int* arr, size_t r, int N, size_t* first, size_t* count ); int main() { int N; /* input variable */ int arr[]={1,1,2,3,3,4,4,4,4,5,5,7,7,7,7,8,8,8,9,11,12,12}; /* array of sorted integers */ size_t r = sizeof(arr)/sizeof(arr[0]); /* right bound */ size_t first; /* first match index */ size_t count; /* total number of matches */ /* prompts the user to enter input */ printf( "\nPlease input the integer you would like to find.\n" ); scanf( "%d", &N ); int a = get_num_of_ints( arr, r, N, &first, &count ); /* If the function returns -1 then the value is not found. Else it is returned */ if( a == -1) printf( "%d has not been found.\n", N ); else if(a >= 0){ printf( "The first matching index is %d.\n", first ); printf( "The total number of instances is %d.\n", count ); } return 0; } /* function definition */ int get_num_of_ints( const int* arr, size_t r, int N, size_t* first, size_t* count ) { int lo=0; /* lower bound for search */ int m=0; /* middle value obtained */ int hi=r-1; /* upper bound for search */ int w=r-1; /* used as a fixed upper bound to calculate the number of right instances of a particular value. */ /* binary search to find if a value exists */ /* first check if the element is out of bounds */ if( N < arr[0] || arr[hi] < N ){ m = -1; } else{ /* binary search to find a value, if it exists, within given parameters */ while(lo <= hi){ m = (hi + lo)/2; if(arr[m] < N) lo = m+1; else if(arr[m] > N) hi = m-1; else if(arr[m]==N){ m=m; break; } } if (lo > hi) /* if it doesn't we assign it -1 */ m = -1; } /* If the value is found, then we compute the left and right instances of it */ if( m >= 0 ){ int j = m-1; /* starting with the first term to the left */ int L = 0; /* total number of left instances */ /* while loop computes total number of left instances */ while( j >= 0 && arr[j] == arr[m] ){ L++; j--; } /* There are six possible outcomes of this. Depending on the outcome, we must assign the first index variable accordingly */ if( j > 0 && L > 0 ) *first=j+1; else if( j==0 && L==0) *first=m; else if( j > 0 && L==0 ) *first=m; else if(j < 0 && L==0 ) *first=m; else if( j < 0 && L > 0 ) *first=0; else if( j=0 && L > 0 ) *first=j+1; int h = m + 1; /* starting with the first term to the right */ int R = 0; /* total number of right instances */ /* while loop computes total number of right instances */ /* we fixed w earlier so that it's value does not change */ while( arr[h]==arr[m] && h <= w ){ R++; h++; } *count = (R + L + 1); /* total number of instances stored as value of count */ return *first; /* first instance index stored here */ } /* if value does not exist, then we return a negative value */ else if( m==-1) return -1; }

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  • Unix sort 10x slower with keys specified

    - by KenFar
    My data: It's a 71 MB file with 1.5 million rows. It has 6 fields, four of which are strings of avg. 15 characters, two are integers. Three of the fields are sometimes empty. All six fields combine to form a unique key - and that's what I need to sort on. Sort statement: sort -t ',' -k1,1 -k2,2 -k3,3 -k4,4 -k5,5 -k6,6 -o a_out.csv a_in.csv The problem: If I sort without keys, it takes 30 seconds. If I sort with keys, it takes 660 seconds. I need to sort with keys to keep this generic and useful for other files that have non-key fields as well. The 30 second timing is fine, but the 660 is a killer. I could theoretically move the temp directory to SSD, and/or split the file into 4 parts, sort them separately (in parallel) then merge the results, etc. But I'm hoping for something simpler since these results are so bad as-is. Any suggestions?

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  • BizTalk Cross Reference Data Management Strategy

    - by charlie.mott
    Article Source: http://geekswithblogs.net/charliemott This article describes an approach to the management of cross reference data for BizTalk.  Some articles about the BizTalk Cross Referencing features can be found here: http://home.comcast.net/~sdwoodgate/xrefseed.zip http://geekswithblogs.net/michaelstephenson/archive/2006/12/24/101995.aspx http://geekswithblogs.net/charliemott/archive/2009/04/20/value-vs.id-cross-referencing-in-biztalk.aspx Options Current options to managing this data include: Maintaining xml files in the format that can be used by the out-of-the-box BTSXRefImport.exe utility. Use of user interfaces that have been developed to manage this data: BizTalk Cross Referencing Tool XRef XML Creation Tool However, there are the following issues with the above options: The 'BizTalk Cross Referencing Tool' requires a separate database to manage.  The 'XRef XML Creation' tool has no means of persisting the data settings. The 'BizTalk Cross Referencing tool' generates integers in the common id field. I prefer to use a string (e.g. acme.country.uk). This is more readable. (see naming conventions below). Both UI tools continue to use BTSXRefImport.exe.  This utility replaces all xref data. This can be a problem in continuous integration environments that support multiple clients or BizTalk target instances.  If you upload the data for one client it would destroy the data for another client.  Yet in TFS where builds run concurrently, this would break unit tests. Alternative Approach In response to these issues, I instead use simple SQL scripts to directly populate the BizTalkMgmtDb xref tables combined with a data namepacing strategy to isolate client data. Naming Conventions All data keys use namespace prefixing.  The pattern will be <companyName>.<data Type>.  The naming conventions will be to use lower casing for all items.  The data must follow this pattern to isolate it from other company cross-reference data.  The table below shows some sample data. (Note: this data uses the 'ID' cross-reference tables.  the same principles apply for the 'value' cross-referencing tables). Table.Field Description Sample Data xref_AppType.appType Application Types acme.erp acme.portal acme.assetmanagement xref_AppInstance.appInstance Application Instances (each will have a corresponding application type). acme.dynamics.ax acme.dynamics.crm acme.sharepoint acme.maximo xref_IDXRef.idXRef Holds the cross reference data types. acme.taxcode acme.country xref_IDXRefData.CommonID Holds each cross reference type value used by the canonical schemas. acme.vatcode.exmpt acme.vatcode.std acme.country.usa acme.country.uk xref_IDXRefData.AppID This holds the value for each application instance and each xref type. GBP USD SQL Scripts The data to be stored in the BizTalkMgmtDb xref tables will be managed by SQL scripts stored in a database project in the visual studio solution. File(s) Description Build.cmd A sqlcmd script to deploy data by running the SQL scripts below.  (This can be run as part of the MSBuild process).   acme.purgexref.sql SQL script to clear acme.* data from the xref tables.  As such, this will not impact data for any other company. acme.applicationInstances.sql   SQL script to insert application type and application instance data.   acme.vatcode.sql acme.country.sql etc ...  There will be a separate SQL script to insert each cross-reference data type and application specific values for these types.

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  • Challenge 19 – An Explanation of a Query

    - by Dave Ballantyne
    I have received a number of requests for an explanation of my winning query of TSQL Challenge 19. This involved traversing a hierarchy of employees and rolling a count of orders from subordinates up to superiors. The first concept I shall address is the hierarchyId , which is constructed within the CTE called cteTree.   cteTree is a recursive cte that will expand the parent-child hierarchy of the personnel in the table @emp.  One useful feature with a recursive cte is that data can be ‘passed’ from the parent to the child data.  The hierarchyId column is similar to the hierarchyId data type that was introduced in SQL Server 2008 and represents the position of the person within the organisation. Let us start with a simplistic example Albert manages Bob and Eddie.  Bob manages Carl and Dave. The hierarchyId will represent each person’s position in this relationship in a single field.  In this simple example we could append the userID together into a varchar field as detailed below. This will enable us to select a branch of the tree by filtering using Where hierarchyId  ‘1,2%’ to select Bob and all his subordinates.  Naturally, this is not comprehensive enough to provide a full solution, but as opposed to concatenating the Id’s together into a varchar datatyped column, we can apply the same theory to a varbinary.  By CASTing the ID’s into a datatype of varbinary(4) ,4 is used as 4 bytes of data are used to store an integer and building a hierarchyId  from those.  For example: The important point to bear in mind for later in the query is that the binary data generated is 'byte order comparable'. ie We can ORDER a dataset with it and the resulting data, will be in the order required. Now, would probably be a good time to download the example file and, after the cte ‘cteTree’, uncomment the line ‘select * from cteTree’.  Mark this and all prior code and execute.  This will show you how this theory directly relates to the actual challenge data.  The only deviation from the above, is that instead of using the ID of an employee, I have used the row_number() ranking function to order each level by LastName,Firstname.  This enables me to order by the HierarchyId in the final result set so that the result set is in the required order. Your output should be something like the below.  Notice also the ‘Level’ Column that contains the depth that the employee is within the tree.  I would encourage you to ‘play’ with the query, change the order in the row_number() or the length of the cast in the hierarchyId to see how that effects the outcome.  The next cte, ‘cteTreeWithOrderCount’, is a join between cteTree and the @ord table, and COUNT’s the number of orders per employee.  A LEFT JOIN is employed here to account for the occasion where an employee has made no sales.   Executing a ‘Select * from cteTreeWithOrderCount’ will return the result set as below.  The order here is unimportant as this is only a staging point of the data and only the final result set in a cte chain needs an Order by clause, unless TOP is utilised. cteExplode joins the above result set to the tally table (Nums) for Level Occurances.  So, if level is 2 then 2 rows are required.  This is done to expand the dataset, to create a new column (PathInc), which is the (n+1) integers contained within the heirarchyid.  For example, with the data for Robert King as given above, the below 3 rows will be returned. From this you can see that the pathinc column now contains the values for Andrew Fuller and Steven Buchanan who are Robert King’s superiors within the tree.    Finally cteSumUp, sums the orders for each person and their subordinates using the PathInc generated above, and the final select does the final simple mathematics and filters to restrict the result set to only the ‘original’ row per employee.

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  • Anatomy of a .NET Assembly - Signature encodings

    - by Simon Cooper
    If you've just joined this series, I highly recommend you read the previous posts in this series, starting here, or at least these posts, covering the CLR metadata tables. Before we look at custom attribute encoding, we first need to have a brief look at how signatures are encoded in an assembly in general. Signature types There are several types of signatures in an assembly, all of which share a common base representation, and are all stored as binary blobs in the #Blob heap, referenced by an offset from various metadata tables. The types of signatures are: Method definition and method reference signatures. Field signatures Property signatures Method local variables. These are referenced from the StandAloneSig table, which is then referenced by method body headers. Generic type specifications. These represent a particular instantiation of a generic type. Generic method specifications. Similarly, these represent a particular instantiation of a generic method. All these signatures share the same underlying mechanism to represent a type Representing a type All metadata signatures are based around the ELEMENT_TYPE structure. This assigns a number to each 'built-in' type in the framework; for example, Uint16 is 0x07, String is 0x0e, and Object is 0x1c. Byte codes are also used to indicate SzArrays, multi-dimensional arrays, custom types, and generic type and method variables. However, these require some further information. Firstly, custom types (ie not one of the built-in types). These require you to specify the 4-byte TypeDefOrRef coded token after the CLASS (0x12) or VALUETYPE (0x11) element type. This 4-byte value is stored in a compressed format before being written out to disk (for more excruciating details, you can refer to the CLI specification). SzArrays simply have the array item type after the SZARRAY byte (0x1d). Multidimensional arrays follow the ARRAY element type with a series of compressed integers indicating the number of dimensions, and the size and lower bound of each dimension. Generic variables are simply followed by the index of the generic variable they refer to. There are other additions as well, for example, a specific byte value indicates a method parameter passed by reference (BYREF), and other values indicating custom modifiers. Some examples... To demonstrate, here's a few examples and what the resulting blobs in the #Blob heap will look like. Each name in capitals corresponds to a particular byte value in the ELEMENT_TYPE or CALLCONV structure, and coded tokens to custom types are represented by the type name in curly brackets. A simple field: int intField; FIELD I4 A field of an array of a generic type parameter (assuming T is the first generic parameter of the containing type): T[] genArrayField FIELD SZARRAY VAR 0 An instance method signature (note how the number of parameters does not include the return type): instance string MyMethod(MyType, int&, bool[][]); HASTHIS DEFAULT 3 STRING CLASS {MyType} BYREF I4 SZARRAY SZARRAY BOOLEAN A generic type instantiation: MyGenericType<MyType, MyStruct> GENERICINST CLASS {MyGenericType} 2 CLASS {MyType} VALUETYPE {MyStruct} For more complicated examples, in the following C# type declaration: GenericType<T> : GenericBaseType<object[], T, GenericType<T>> { ... } the Extends field of the TypeDef for GenericType will point to a TypeSpec with the following blob: GENERICINST CLASS {GenericBaseType} 3 SZARRAY OBJECT VAR 0 GENERICINST CLASS {GenericType} 1 VAR 0 And a static generic method signature (generic parameters on types are referenced using VAR, generic parameters on methods using MVAR): TResult[] GenericMethod<TInput, TResult>( TInput, System.Converter<TInput, TOutput>); GENERIC 2 2 SZARRAY MVAR 1 MVAR 0 GENERICINST CLASS {System.Converter} 2 MVAR 0 MVAR 1 As you can see, complicated signatures are recursively built up out of quite simple building blocks to represent all the possible variations in a .NET assembly. Now we've looked at the basics of normal method signatures, in my next post I'll look at custom attribute application signatures, and how they are different to normal signatures.

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  • Surviving MATLAB and R as a Hardcore Programmer

    - by dsimcha
    I love programming in languages that seem geared towards hardcore programmers. (My favorites are Python and D.) MATLAB is geared towards engineers and R is geared towards statisticians, and it seems like these languages were designed by people who aren't hardcore programmers and don't think like hardcore programmers. I always find them somewhat awkward to use, and to some extent I can't put my finger on why. Here are some issues I have managed to identify: (Both): The extreme emphasis on vectors and matrices to the extent that there are no true primitives. (Both): The difficulty of basic string manipulation. (Both): Lack of or awkwardness in support for basic data structures like hash tables and "real", i.e. type-parametric and nestable, arrays. (Both): They're really, really slow even by interpreted language standards, unless you bend over backwards to vectorize your code. (Both): They seem to not be designed to interact with the outside world. For example, both are fairly bulky programs that take a while to launch and seem to not be designed to make simple text filter programs easy to write. Furthermore, the lack of good string processing makes file I/O in anything but very standard forms near impossible. (Both): Object orientation seems to have a very bolted-on feel. Yes, you can do it, but it doesn't feel much more idiomatic than OO in C. (Both): No obvious, simple way to get a reference type. No pointers or class references. For example, I have no idea how you roll your own linked list in either of these languages. (MATLAB): You can't put multiple top level functions in a single file, encouraging very long functions and cut-and-paste coding. (MATLAB): Integers apparently don't exist as a first class type. (R): The basic builtin data structures seem way too high level and poorly documented, and never seem to do quite what I expect given my experience with similar but lower level data structures. (R): The documentation is spread all over the place and virtually impossible to browse or search. Even D, which is often knocked for bad documentation and is still fairly alpha-ish, is substantially better as far as I can tell. (R): At least as far as I'm aware, there's no good IDE for it. Again, even D, a fairly alpha-ish language with a small community, does better. In general, I also feel like MATLAB and R could be easily replaced by plain old libraries in more general-purpose langauges, if sufficiently comprehensive libraries existed. This is especially true in newer general purpose languages that include lots of features for library writers. Why do R and MATLAB seem so weird to me? Are there any other major issues that you've noticed that may make these languages come off as strange to hardcore programmers? When their use is necessary, what are some good survival tips? Edit: I'm seeing one issue from some of the answers I've gotten. I have a strong personal preference, when I analyze data, to have one script that incorporates the whole pipeline. This implies that a general purpose language needs to be used. I hate having to write a script to "clean up" the data and spit it out, then another to read it back in a completely different environment, etc. I find the friction of using MATLAB/R for some of my work and a completely different language with a completely different address space and way of thinking for the rest to be a huge source of friction. Furthermore, I know there are glue layers that exist, but they always seem to be horribly complicated and a source of friction.

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  • Improving the running time of Breadth First Search and Adjacency List creation

    - by user45957
    We are given an array of integers where all elements are between 0-9. have to start from the 1st position and reach end in minimum no of moves such that we can from an index i move 1 position back and forward i.e i-1 and i+1 and jump to any index having the same value as index i. Time Limit : 1 second Max input size : 100000 I have tried to solve this problem use a single source shortest path approach using Breadth First Search and though BFS itself is O(V+E) and runs in time the adjacency list creation takes O(n2) time and therefore overall complexity becomes O(n2). is there any way i can decrease the time complexity of adjacency list creation? or is there a better and more efficient way of solving the problem? int main(){ vector<int> v; string str; vector<int> sets[10]; cin>>str; int in; for(int i=0;i<str.length();i++){ in=str[i]-'0'; v.push_back(in); sets[in].push_back(i); } int n=v.size(); if(n==1){ cout<<"0\n"; return 0; } if(v[0]==v[n-1]){ cout<<"1\n"; return 0; } vector<int> adj[100001]; for(int i=0;i<10;i++){ for(int j=0;j<sets[i].size();j++){ if(sets[i][j]>0) adj[sets[i][j]].push_back(sets[i][j]-1); if(sets[i][j]<n-1) adj[sets[i][j]].push_back(sets[i][j]+1); for(int k=j+1;k<sets[i].size();k++){ if(abs(sets[i][j]-sets[i][k])!=1){ adj[sets[i][j]].push_back(sets[i][k]); adj[sets[i][k]].push_back(sets[i][j]); } } } } queue<int> q; q.push(0); int dist[100001]; bool visited[100001]={false}; dist[0]=0; visited[0]=true; int c=0; while(!q.empty()){ int dq=q.front(); q.pop(); c++; for(int i=0;i<adj[dq].size();i++){ if(visited[adj[dq][i]]==false){ dist[adj[dq][i]]=dist[dq]+1; visited[adj[dq][i]]=true; q.push(adj[dq][i]); } } } cout<<dist[n-1]<<"\n"; return 0; }

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  • How to use correctly the comments in C/++

    - by Lucio
    I'm learning to program in C and in my stage, the best form to use correctly the comments is writing good comments from the beginning. As the comments are not just for that one understands better the code but others too, I want to know the views of all of you to reach a consensus. So what I want is that the most experienced users edit the following code as you please. (If it's unnecessary, delete it; If it's wrong, correct it; If needed, add more) Thus there'll be multiple answers with different syntax and the responses with the most votes will be taken as referring when commenting. The code to copy, paste and edit to your pleasure is: (And I remark again, just import the comments, not the code) /* This programs find 1 number in 1 file. The file is binary type and has integers in series. The number is integer type and it's entered from the keyboard. When finished the program, a poster will show the results: Saying if the number is in the file or not. */ #include <stdio.h> //FUNCTION 1 //Open file 'path' and closes it. void openf(char path[]) { int num; //Read from Keyboard a Number and it save it into 'num' var printf("Ready for read number.\n\nNumber --> "); fflush(stdin); scanf("%d",&num); //Open file 'path' in READ mode FILE *fvar; fvar=fopen(path,"rb"); //IF error happens when open file, exit of function if (fvar==NULL) { printf("ERROR while open file %s in read mode.",path); exit(1); } /*Verify the result of 'funct' function IF TRUE, 'num' it's in the file*/ if (funct(path,fvar,num)) printf("The number %d it is in the file %s.",num,path); else printf("The number %d it is not in the file %s.",num,path); fclose(fvar); } /*FUNCTION 2 It is a recursive function. Reads number by number until the file is empty or the number is found. Parameters received: 'path' -> Directory file 'fvar' -> Pointer file 'num' -> Number to compare */ int funct(char path[],FILE *fvar,int num) { int compare; //FALSE condition when the pointer reaches the end if (fread(&compare,sizeof(int),1,fvar)>0) /*TRUE condition when the number readed is iqual that 'num' ELSE will go to the function itself*/ if (compare!=num) funct(path,fvar,num); else return 1; else return 0; } int main(int argc, char **argv) { char path[30]="file.bin"; //Direction of the file to process openf(path); //Function with algorithm return 0; }

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  • concurrency::extent<N> from amp.h

    - by Daniel Moth
    Overview We saw in a previous post how index<N> represents a point in N-dimensional space and in this post we'll see how to define the N-dimensional space itself. With C++ AMP, an N-dimensional space can be specified with the template class extent<N> where you define the size of each dimension. From a look and feel perspective, you'd expect the programmatic interface of a point type and size type to be similar (even though the concepts are different). Indeed, exactly like index<N>, extent<N> is essentially a coordinate vector of N integers ordered from most- to least- significant, BUT each integer represents the size for that dimension (and hence cannot be negative). So, if you read the description of index, you won't be surprised with the below description of extent<N> There is the rank field returning the value of N you passed as the template parameter. You can construct one extent from another (via the copy constructor or the assignment operator), you can construct it by passing an integer array, or via convenience constructor overloads for 1- 2- and 3- dimension extents. Note that the parameterless constructor creates an extent of the specified rank with all bounds initialized to 0. You can access the components of the extent through the subscript operator (passing it an integer). You can perform some arithmetic operations between extent objects through operator overloading, i.e. ==, !=, +=, -=, +, -. There are operator overloads so that you can perform operations between an extent and an integer: -- (pre- and post- decrement), ++ (pre- and post- increment), %=, *=, /=, +=, –= and, finally, there are additional overloads for plus and minus (+,-) between extent<N> and index<N> objects, returning a new extent object as the result. In addition to the usual suspects, extent offers a contains function that tests if an index is within the bounds of the extent (assuming an origin of zero). It also has a size function that returns the total linear size of this extent<N> in units of elements. Example code extent<2> e(3, 4); _ASSERT(e.rank == 2); _ASSERT(e.size() == 3 * 4); e += 3; e[1] += 6; e = e + index<2>(3,-4); _ASSERT(e == extent<2>(9, 9)); _ASSERT( e.contains(index<2>(8, 8))); _ASSERT(!e.contains(index<2>(8, 9))); grid<N> Our upcoming pre-release bits also have a similar type to extent, grid<N>. The way you create a grid is by passing it an extent, e.g. extent<3> e(4,2,6); grid<3> g(e); I am not going to dive deeper into grid, suffice for now to think of grid<N> simply as an alias for the extent<N> object, that you create when you encounter a function that expects a grid object instead of an extent object. Usage The extent class on its own simply defines the size of the N-dimensional space. We'll see in future posts that when you create containers (arrays) and wrappers (array_views) for your data, it is an extent<N> object that you'll need to use to create those (and use an index<N> object to index into them). We'll also see that it is a grid<N> object that you pass to the new parallel_for_each function that I'll cover in the next post. Comments about this post by Daniel Moth welcome at the original blog.

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  • Making flexible C# code in MVC2 for Stored Procedures

    - by cc0
    Thanks to Darin Dimitrov's suggestion I got a big step further in understanding good MVC code, but I'm having some problems making it flexible. I implemented Darin's suggested solution, and it works perfectly for single controllers. However I'm having some trouble implementing it with some flexibility. What I'm looking for is this; To be able to make dynamic column names in json Instead of using "Column1: 'value', ..." and "Column2: 'value', ..." inside the json, I'd like to use for example "id: 'value', ..." and "place: 'value' ..." for one stored procedure, and "animal" and "type" in another (inside the json format). To be able to make dynamic amounts of columns dependent on which stored procedure is called Some stored procedures I'll want to read more than 2 rows from, is there a smart way of accomplishing that? To be able to make numeric (floats and integers) rows from the database be presented inside the json without quotes Like this (name and age); { Column1: "John", Column2: 53 }, I would be very grateful for any feedback and suggestions / code examples I can get here. Even imperfect ones.

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  • Code Golf: Collatz Conjecture

    - by Earlz
    Inspired by http://xkcd.com/710/ here is a code golf for it. The Challenge Given a positive integer greater than 0, print out the hailstone sequence for that number. The Hailstone Sequence See Wikipedia for more detail.. If the number is even, divide it by two. If the number is odd, triple it and add one. Repeat this with the number produced until it reaches 1. (if it continues after 1, it will go in an infinite loop of 1 -> 4 -> 2 -> 1...) Sometimes code is the best way to explain, so here is some from Wikipedia function collatz(n) show n if n > 1 if n is odd call collatz(3n + 1) else call collatz(n / 2) This code works, but I am adding on an extra challenge. The program must not be vulnerable to stack overflows. So it must either use iteration or tail recursion. Also, bonus points for if it can calculate big numbers and the language does not already have it implemented. (or if you reimplement big number support using fixed-length integers) Test case Number: 21 Results: 21 -> 64 -> 32 -> 16 -> 8 -> 4 -> 2 -> 1 Number: 3 Results: 3 -> 10 -> 5 -> 16 -> 8 -> 4 -> 2 -> 1 Also, the code golf must include full user input and output.

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  • Help improving a simple assembly function

    - by MPelletier
    I just handed in this function in an assignment. It is done (hence no homework tag). But I would like to see how this can be improved. Essentially, the function sums the squares of all the integers between 1 and the given number, using the following formula: n(n+1)(2n+1)/6 Where n is the maximum number. The function below is made to catch any overflow and return 0 should any occur. UInt32 sumSquares(const UInt32 number) { int result = 0; __asm { mov eax, number //move number in eax mov edx, 2 //move 2 in edx mul edx //multiply (2n) jo end //jump to end if overflow add eax, 1 //addition (2n+1) jo end //jump to end if overflow mov ecx, eax //move (2n+1) in ecx mov ebx, number //move number in ebx add ebx, 1 //addition (n+1) jo end //jump to end if overflow mov eax, number //move number in eax for multiplication mul ebx //multiply n(n+1) jo end //jump to end if overflow mul ecx //multiply n(n+1)(2n+1) jo end //jump to end if overflow mov ebx, 6 //move 6 in ebx div ebx //divide by 6, the result will be in eax mov result, eax //move eax in result end: } return result; } Basically, I want to know what I can improve in there. In terms of best-practices mostly. One thing sounds obvious: smarter overflow check (with a single check for whatever maximum input would cause an overflow).

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  • C# average function for large numbers without overflow exception

    - by Ron Klein
    .NET Framework 3.5. I'm trying to calculate the average of some pretty large numbers. For instance: using System; using System.Linq; class Program { static void Main(string[] args) { var items = new long[] { long.MaxValue - 100, long.MaxValue - 200, long.MaxValue - 300 }; try { var avg = items.Average(); Console.WriteLine(avg); } catch (OverflowException ex) { Console.WriteLine("can't calculate that!"); } Console.ReadLine(); } } Obviously, the mathematical result is 9223372036854775607 (long.MaxValue - 200), but I get an exception there. This is because the implementation (on my machine) to the Average extension method, as inspected by .NET Reflector is: public static double Average(this IEnumerable<long> source) { if (source == null) { throw Error.ArgumentNull("source"); } long num = 0L; long num2 = 0L; foreach (long num3 in source) { num += num3; num2 += 1L; } if (num2 <= 0L) { throw Error.NoElements(); } return (((double) num) / ((double) num2)); } I know I can use a BigInt library (yes, I know that it is included in .NET Framework 4.0, but I'm tied to 3.5). But I still wonder if there's a pretty straight forward implementation of calculating the average of integers without an external library. Do you happen to know about such implementation? Thanks!!

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  • What's the recommended implemenation for hashing OLE Variants?

    - by Barry Kelly
    OLE Variants, as used by older versions of Visual Basic and pervasively in COM Automation, can store lots of different types: basic types like integers and floats, more complicated types like strings and arrays, and all the way up to IDispatch implementations and pointers in the form of ByRef variants. Variants are also weakly typed: they convert the value to another type without warning depending on which operator you apply and what the current types are of the values passed to the operator. For example, comparing two variants, one containing the integer 1 and another containing the string "1", for equality will return True. So assuming that I'm working with variants at the underlying data level (e.g. VARIANT in C++ or TVarData in Delphi - i.e. the big union of different possible values), how should I hash variants consistently so that they obey the right rules? Rules: Variants that hash unequally should compare as unequal, both in sorting and direct equality Variants that compare as equal for both sorting and direct equality should hash as equal It's OK if I have to use different sorting and direct comparison rules in order to make the hashing fit. The way I'm currently working is I'm normalizing the variants to strings (if they fit), and treating them as strings, otherwise I'm working with the variant data as if it was an opaque blob, and hashing and comparing its raw bytes. That has some limitations, of course: numbers 1..10 sort as [1, 10, 2, ... 9] etc. This is mildly annoying, but it is consistent and it is very little work. However, I do wonder if there is an accepted practice for this problem.

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  • Conditional Regular Expression testing of a CSV

    - by Alastair Pitts
    I am doing some client side validation in ASP.NET MVC and I found myself trying to do conditional validation on a set of items (ie, if the checkbox is checked then validate and visa versa). This was problematic, to say the least. To get around this, I figured that I could "cheat" by having a hidden element that would contain all of the information for each set, thus the idea of a CSV string containing this information. I already use a custom [HiddenRequired] attribute to validate if the hidden input contains a value, with success, but I thought as I will need to validate each piece of data in the csv, that a regular expression would solve this. My regular expression work is extremely weak and after a good 2 hours I've almost given up. This is an example of the csv string: true,3,24,over,0.5 to explain: true denotes if I should validate the rest. I need to conditionally switch in the regex using this 3 and 24 are integers and will only ever fall in the range 0-24. over is a string and will either be over or under 0.5 is a decimal value, of unknown precision. In the validation, all values should be present and at least of the correct type Is there someone who can either provide such a regex or at least provide some hints, i'm really stuck!

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  • The Date type and the Android database

    - by cdonner
    I understand that SQLite stores dates as long integers. When I read rows into a cursor using the standard method (i.e. using the query() method that reads data into a cursor), the result is a date string that includes the time. If I want a different format, I have to parse the string back into a date - possible, but a bit backwards. By using a ViewBinder (as suggested in this question), I can pretty much do anything I want, but the date is already a string at the time the method executes. The accepted answer to the above question also suggests that storing dates as longs would help avoid this problem. I don't want to do that, just in case I want to interpret my data with something else than this application. Maybe I want to expose it via a provider. Is there a way to handle this in the database adapter instead, i.e. controlling the date format that the cursor contains, so that I don't have to change the schema, and don't have to parse the default output back into a Date type?

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  • Deleting JPA entity containing @CollectionOfElements throws ConstraintViolationException

    - by Lyle
    I'm trying to delete entities which contain lists of Integer, and I'm getting ConstraintViolationExceptions because of the foreign key on the table generated to hold the integers. It appears that the delete isn't cascading to the mapped collection. I've done quite a bit of searching, but all of the examples I've seen on how to accomplish this are in reference to a mapped collection of other entities which can be annotated; here I'm just storing a list of Integer. Here is the relevant excerpt from the class I'm storing: @Entity @Table(name="CHANGE_IDS") @GenericGenerator( name = "CHANGE_ID_GEN", strategy = "org.hibernate.id.enhanced.SequenceStyleGenerator", parameters = { @Parameter(name="sequence_name", value="course_changes_seq"), @Parameter(name="increment_size", value="5000"), @Parameter(name=" optimizer", value="pooled") } ) @NamedQueries ({ @NamedQuery( name="Changes.getByStatus", query= "SELECT c " + "FROM DChanges c " + "WHERE c.status = :status "), @NamedQuery( name="Changes.deleteByStatus", query= "DELETE " + "FROM Changes c " + "WHERE c.status = :status ") }) public class Changes { @Id @GeneratedValue(generator="CHANGE_ID_GEN") @Column(name = "ID") private final long id; @Enumerated(EnumType.STRING) @Column(name = "STATUS", length = 20, nullable = false) private final Status status; @Column(name="DOC_ID") @org.hibernate.annotations.CollectionOfElements @org.hibernate.annotations.IndexColumn(name="DOC_ID_ORDER") private List<Integer> docIds; } I'm deleting the Changes objects using a @NamedQuery: final Query deleteQuery = this.entityManager.createNamedQuery("Changes.deleteByStatus"); deleteQuery.setParameter("status", Status.POST_FLIP); final int deleted = deleteQuery.executeUpdate(); this.logger.info("Deleted " + deleted + " POST_FLIP Changes");

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  • Cannot update a single field using Linq to Sql

    - by KallDrexx
    I am having a hard time attempting to update a single field without having to retrieve the whole record prior to saving. For example, in my web application I have an in place editor for the Name and Description fields of an object. Once you edit either field, it sends the new field (with the object's ID value) to the web server. What I want is the webserver to take that value and ID and only update the one field. There are only two ways google tells me to do this: 1) When I get the value I want to change, the value and the ID, retrieve the record from the database, update the field in the c# object, and then send it back to the server. I don't like this method because not only does it include a completely unnecessary database read call (which includes two tables due to the way my schema is). 2) Set UpdateCheck for all the fields (but the primary keys) to UpdateCheck.Never. This doesn't work for me (I think) due to my mapping layer between the Linq to Sql and my Entity/ViewModel layer. When I convert my entity into the linq to sql db object it seems to be updating those fields regardless of the UpdateCheck setting. This might be just because of integers, since not setting an int means it is a zero (and no, I can't use int? instead). Are there any other options that I have?

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  • Why is setting HTML5's CanvasPixelArray values ridiculously slow and how can I do it faster?

    - by Nixuz
    I am trying to do some dynamic visual effects using the HTML 5 canvas' pixel manipulation, but I am running into a problem where setting pixels in the CanvasPixelArray is ridiculously slow. For example if I have code like: imageData = ctx.getImageData(0, 0, 500, 500); for (var i = 0; i < imageData.length; i += 4){ imageData.data[i] = buffer[i]; imageData.data[i + 1] = buffer[i + 1]; imageData.data[i + 2] = buffer[i + 2]; } ctx.putImageData(imageData, 0, 0); Profiling with Chrome reveals, it runs 44% slower than the following code where CanvasPixelArray is not used. tempArray = new Array(500 * 500 * 4); imageData = ctx.getImageData(0, 0, 500, 500); for (var i = 0; i < imageData.length; i += 4){ tempArray[i] = buffer[i]; tempArray[i + 1] = buffer[i + 1]; tempArray[i + 2] = buffer[i + 2]; } ctx.putImageData(imageData, 0, 0); My guess is that the reason for this slowdown is due to the conversion between the Javascript doubles and the internal unsigned 8bit integers, used by the CanvasPixelArray. Is this guess correct? Is there anyway to reduce the time spent setting values in the CanvasPixelArray?

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  • Simple Program Question (TI-84 calculator)

    - by John
    I wrote a program (on my TI-84 calculator) to satisfy the following exercise: Write a program that will print all solutions of the inequality ax + b < c, where a, b, and c are entered by the user. In this program the domain of x will be a set of consecutive integers, where the smallest and largest members of the set will also be entered by the user. (Hint: Use a FOR . . . NEXT loop to test each integer from smallest to largest.) This is the code I have: :Input "A=",A :Input "B=",B :Input "C=",C :Disp "DOMAIN FOR X" :Input "MIN=",D :Input "MAX=",E :For(X,D,E,1) :If AX+B<C :Disp X :End I sort of figured it out by chance; I don't really know how 'If' works inside 'For.' I wanted to have it tell me if there is no solution, though, so I tried: :Input "A=",A :Input "B=",B :Input "C=",C :Disp "DOMAIN FOR X" :Input "MIN=",D :Input "MAX=",E :For(X,D,E,1) :If AX+B<C :Then :Disp X :Else :Disp "NO SOLUTION" :End But this returns the value for "MIN=" Why is this? Can anyone help me understand these work?

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  • Subset a data.frame by list and apply function on each part, by rows

    - by aL3xa
    This may seem as a typical plyr problem, but I have something different in mind. Here's the function that I want to optimize (skip the for loop). # dummy data set.seed(1985) lst <- list(a=1:10, b=11:15, c=16:20) m <- matrix(round(runif(200, 1, 7)), 10) m <- as.data.frame(m) dfsub <- function(dt, lst, fun) { # check whether dt is `data.frame` stopifnot (is.data.frame(dt)) # check if vectors in lst are "whole" / integer # vector elements should be column indexes is.wholenumber <- function(x, tol = .Machine$double.eps^0.5) abs(x - round(x)) < tol # fall if any non-integers in list idx <- rapply(lst, is.wholenumber) stopifnot(idx) # check for list length stopifnot(ncol(dt) == length(idx)) # subset the data subs <- list() for (i in 1:length(lst)) { # apply function on each part, by row subs[[i]] <- apply(dt[ , lst[[i]]], 1, fun) } # preserve names names(subs) <- names(lst) # convert to data.frame subs <- as.data.frame(subs) # guess what =) return(subs) } And now a short demonstration... actually, I'm about to explain what I primarily intended to do. I wanted to subset a data.frame by vectors gathered in list object. Since this is a part of code from a function that accompanies data manipulation in psychological research, you can consider m as a results from personality questionnaire (10 subjects, 20 vars). Vectors in list hold column indexes that define questionnaire subscales (e.g. personality traits). Each subscale is defined by several items (columns in data.frame). If we presuppose that the score on each subscale is nothing more than sum (or some other function) of row values (results on that part of questionnaire for each subject), you could run: > dfsub(m, lst, sum) a b c 1 46 20 24 2 41 24 21 3 41 13 12 4 37 14 18 5 57 18 25 6 27 18 18 7 28 17 20 8 31 18 23 9 38 14 15 10 41 14 22 I took a glance at this function and I must admit that this little loop isn't spoiling the code at all... BUT, if there's an easier/efficient way of doing this, please, let me know!

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