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  • Call Python From PHP And Get Return Code

    - by seaboy
    Hello everyone, I am calling a python script from PHP. The python program has to return some value according to the arguments passed to it. Here is a sample python program, which will give you a basic idea of what i am doing currently: #!/usr/bin/python import sys #get the arguments passed argList = sys.argv #Not enough arguments. Exit with a value of 1. if len(argList) < 3: #Return with a value of 1. sys.exit(1) arg1 = argList[1] arg2 = argList[2] #Check arguments. Exit with the appropriate value. if len(arg1) > 255: #Exit with a value of 4. sys.exit(4) if len(arg2) < 2: #Exit with a value of 8. sys.exit(8) #Do further coding using the arguments------ #If program works successfully, exit with a value of 0 As you can see from the above code, my basic aim is for the python program to return some values (0,1,4,8 etc) depending on the arguments. And then the calling PHP program to access these returned values and do the appropriate operation. Currently i have used "sys.exit(n)", for that purpose. Am i right in using sys.exit, or do I need to use something else? And also what method exists in PHP so that I can access the return code from python? Sorry for the long question, but hopefully it will help in you understanding my dilemma Thanks a ton

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  • A weird crash...

    - by Nima
    Hi, I have a piece of code that runs in debug mode in VS2008, C++. The problem is that when I am debugging the code line by line, at a very weird point of the code, it crashes and says: debug assertion faild. Expression: _BLOCK_TYPE_IS_VALID(pHead-nBlockUse) The crash point is on the first closed curly bracket (after mesh-edges[e].needsUpdate=false;) I don't understand why on a curly bracket? does that make sense to you guys? Can anybody help me understanding what is going on..? for(int e=0; e<mesh->edges.size(); e++) { if(mesh->edges[e].valid && mesh->edges[e].v[0]>=0 && mesh->edges[e].v[1]>=0 && mesh->points[mesh->edges[e].v[0]].writable && mesh->points[mesh->edges[e].v[1]].writable) { //update v_hat and its corresponding error DecEdge Current = DecEdge(e); pair<Point, float> ppf = computeVhat(e); Current.v_hat = ppf.first; Current.error = ppf.second; edgeSoup.push(Current); mesh->edges[e].needsUpdate=false; } }

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  • boost::shared_ptr in Objective-C++

    - by John Smith
    This is a better understanding of a question I had earlier. I have the following Objective-C++ object @interface OCPP { MyCppobj * cppobj; } @end @implementation OCPP -(OCPP *) init { cppobj = new MyCppobj; } @end Then I create a completely differently obj which needs to use cppobj in a boost::shared_ptr (I have no choice in this matter, it's part of a huge library which I cannot change) @interface NOBJ -(void) use_cppobj_as_shared_ptr { //get an OCPP obj called occ from somewhere.. //troubling line here } @end I have tried the following and that failed: I tried synthesising cppobj. Then I created a shared_ptr in "troubling line" in the following way: MyCppobj * cpp = [occ cppobj]; bsp = boost::shared_ptr<MyCppobj>(cpp); It works fine first time around. Then I destroy the NOBJ and recreate it. When I for cppobj it's gone. Presumably shared_ptr decided it's no longer needed and did away with it. So I need help. How can I keep cppobj alive? Is there a way to destroy bsp (or it's reference to cppobj) without destroying cppobj?

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  • Please take a stab at this VB.Net Oracle-related sample and help me with String.Format.

    - by Hamish Grubijan
    If the database is not Oracle, it is MS SQl 2008. My task: if Oracle, add two more parameters when calling a stored proc. Oracle and MSFT stored procs are generated; Oracle ones have 3 extra parameters: Vret_val out number, Vparam2 in out number, Vparam3 in out number, ... the rest (The are not actually named Vparam2 and Vparam3, but this should not matter). So, the code for a helper VB.Net class that calls a stored proc: Imports System.Data.Odbc Imports System.Configuration Dim objCon As OdbcConnection = Nothing Dim objAdapter As OdbcDataAdapter Dim cmdCommand As New OdbcCommand Dim objDataTable As DataTable Dim sconnection As String Try sconnection = mConnectionString objAdapter = New OdbcDataAdapter objCon = New OdbcConnection(sconnection) objCon.Open() objAdapter.SelectCommand = cmdCommand objAdapter.SelectCommand.Connection = objCon objAdapter.SelectCommand.CommandType = CommandType.StoredProcedure objAdapter.SelectCommand.CommandTimeout = Globals.mReportTimeOut If Not mIsOracle Then objAdapter.SelectCommand.CommandText = String.Format("{{call {0}}}", spName) Else Dim returnValue As New OdbcParameter returnValue.Direction = ParameterDirection.Output returnValue.ParameterName = "@Vret_val" returnValue.OdbcType = OdbcType.Numeric objAdapter.SelectCommand.Parameters.Add(returnValue) objAdapter.SelectCommand.CommandText = String.Format("{{call {0}(?)}}", spName) End If Try objDataTable = New DataTable(spName) objAdapter.Fill(objDataTable) Catch ex As Exception ... Question: I am puzzled as to what String.Format("{{call {0}(?)}}", spName) does, in particular the (?) part. My understanding of the String.Format is that it will simply replace {0} with spName. The {{, }}, and (?) do throw me off because { reminds me of formatting, (?) hints at some advanced regex use. Unfortunately I am getting little help from a key person who is on vacation without a leash [smart]phone. I am guessing that I simply add 5 more lines for each additional parameter, and change String.Format("{{call {0}(?)}}", spName) to String.Format("{{call {0}(?,?,?)}}", spName). I forgot to mention that I am coding this "blindly" - I have a compiler to help me, but no environment set up to test this. This will be over in a few days, but I need to do my best to try finishing it on time :) Thanks.

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  • Data Annotations on ViewModels or Domain Objects

    - by Ahmad
    Where would data annotations be more suitable: ViewModels or Domain Objects or Both I am struggling to decide where these will be more suited. I have not as yet fully utilized them but this question came to mind. From most of the examples I have seen, they are generally placed on Models and simply use the required attributes for validation using ModelState.IsValid. I have also seen another question on SO where the use of data annotations alone is not sufficient and advocate. Option 1 - I will still need to validate again in my service layer. ( I think that my service layer should be complete and this include validation, since its planned to be used elsewhere) Option 2 - How will I then get the benefits of the built in validation both client and server side. Option 3 - there will be a repetition of validation logic, however I was wondering if one could use a MetaData class approach that can be used for both ViewModels and Domain Objects. ( This is completely of the top of my head, so it may be nonsensical) I wonder if this question even makes sense. If not, can someone please help in understanding this better. Have I completely misunderstood the use of data annotations?

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  • Is my objective possible using WCF (and is it the right way to do things?)

    - by David
    I'm writing some software that modifies a Windows Server's configuration (things like MS-DNS, IIS, parts of the filesystem). My design has a server process that builds an in-memory object graph of the server configuration state and a client which requests this object graph. The server would then serialize the graph, send it to the client (presumably using WCF), the server then makes changes to this graph and sends it back to the server. The server receives the graph and proceeds to make modifications to the server. However I've learned that object-graph serialisation in WCF isn't as simple as I first thought. My objects have a hierarchy and many have parametrised-constructors and immutable properties/fields. There are also numerous collections, arrays, and dictionaries. My understanding of WCF serialisation is that it requires use of either the XmlSerializer or DataContractSerializer, but DCS places restrictions on the design of my object-graph (immutable data seems right-out, it also requires parameter-less constructors). I understand XmlSerializer lets me use my own classes provided they implement ISerializable and have the de-serializer constructor. That is fine by me. I spoke to a friend of mine about this, and he advocates going for a Data Transport Object-only route, where I'd have to maintain a separate DataContract object-graph for the transport of data and re-implement my server objects on the client. Another friend of mine said that because my service only has two operations ("GetServerConfiguration" and "PutServerConfiguration") it might be worthwhile just skipping WCF entirely and implementing my own server that uses Sockets. So my questions are: Has anyone faced a similar problem before and if so, are there better approaches? Is it wise to send an entire object graph to the client for processing? Should I instead break it down so that the client requests a part of the object graph as it needs it and sends only bits that have changed (thus reducing concurrency-related risks?)? If sending the object-graph down is the right way, is WCF the right tool? And if WCF is right, what's the best way to get WCF to serialise my object graph?

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  • Does adding to a method group count as using a variable?

    - by Vaccano
    I have the following code example taken from the code of a Form: protected void SomeMethod() { SomeOtherMethod(this.OnPaint); } private void SomeOtherMethod(Action<PaintEventArgs> onPaint) { onPaint += MyPaint; } protected void MyPaint(PaintEventArgs e) { // paint some stuff } The second method (SomeOtherMethod) has resharper complaining at me. It says of onPaint that "Value assigned is not used in any execution path". To my mind it was used because I added a method to the list of methods called when a paint was done. But usually when resharper tells me something like this it is because I am not understanding some part of C#. Like maybe when the param goes out of goes out of scope the item I added to the list gets removed (or something like that). I thought I would ask here to see if any one knows what resharper is trying to tell me. (Side Note: I usually just override OnPaint. But I am trying to get OnPaint to call a method in another class. I don't want to expose that method publicly so I thought I would pass in the OnPaint group and add to it.)

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  • Trouble with custom WPF Panel-derived class

    - by chaiguy
    I'm trying to write a custom Panel class for WPF, by overriding MeasureOverride and ArrangeOverride but, while it's mostly working I'm experiencing one strange problem I can't explain. In particular, after I call Arrange on my child items in ArrangeOverride after figuring out what their sizes should be, they aren't sizing to the size I give to them, and appear to be sizing to the size passed to their Measure method inside MeasureOverride. Am I missing something in how this system is supposed to work? My understanding is that calling Measure simply causes the child to evaluate its DesiredSize based on the supplied availableSize, and shouldn't affect its actual final size. Here is my full code (the Panel, btw, is intended to arrange children in the most space-efficient manner, giving less space to rows that don't need it and splitting remaining space up evenly among the rest--it currently only supports vertical orientation but I plan on adding horizontal once I get it working properly): protected override Size MeasureOverride( Size availableSize ) { foreach ( UIElement child in Children ) child.Measure( availableSize ); return availableSize; } protected override System.Windows.Size ArrangeOverride( System.Windows.Size finalSize ) { double extraSpace = 0.0; var sortedChildren = Children.Cast<UIElement>().OrderBy<UIElement, double>( new Func<UIElement, double>( delegate( UIElement child ) { return child.DesiredSize.Height; } ) ); double remainingSpace = finalSize.Height; double normalSpace = 0.0; int remainingChildren = Children.Count; foreach ( UIElement child in sortedChildren ) { normalSpace = remainingSpace / remainingChildren; if ( child.DesiredSize.Height < normalSpace ) // if == there would be no point continuing as there would be no remaining space remainingSpace -= child.DesiredSize.Height; else { remainingSpace = 0; break; } remainingChildren--; } extraSpace = remainingSpace / Children.Count; double offset = 0.0; foreach ( UIElement child in Children ) { //child.Measure( new Size( finalSize.Width, normalSpace ) ); double value = Math.Min( child.DesiredSize.Height, normalSpace ) + extraSpace; child.Arrange( new Rect( 0, offset, finalSize.Width, value ) ); offset += value; } return finalSize; }

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  • Common NSNotification mistakes?

    - by Ben Packard
    A simplification... A building has an array of apartment objects. Each apartment has a single currentTenant. These tenants are of type Person. Note that currentTenant doesn't have a reference to the apartment, so can't send information back up the chain. When a tenant has a plumbing issue he raises an NSNotification: [nc postNotificationName:@"PlumbingIssue" object:self]; Each Apartment observes notifications ONLY FROM it's own current tenant (this is set up when the apartment is built, before there is a current tenant): [nc addObserver:self selector:@selector(alertBuildingManager:) name:@"PlumbingIssue" object:[self currentTenant]; When the apartment receives a notification from it's own currentTenant, it sends it's own notification, "PlumberRequired", along with the apartment number and the currentTenant in an NSDictionary. Apartment observes these notifications, which it will take from any apartment (or other object): [nc addObserver:self selector:@selector(callPlumber) name:@"PlumberRequired" object:nil]; Is there something I could be getting fundamentally wrong here? What's happening is that the apartment is receiving notifications from any and all currentTenants, rather than jus it's own. Sorry that the actual code is a bit too unwieldy to post. Was just wondering if there's a gap in my understanding about observing notifications from a particular sender?

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  • C# internal VS VBNET Friend

    - by Will Marcouiller
    To this SO question: What is the C# equivalent of friend?, I would personally have answered "internal", just like Ja did among the answers! However, Jon Skeet says that there is no direct equivalence of VB Friend in C#. If Jon Skeet says so, I won't be the one telling otherwise! ;P I'm wondering how can the keyword internal (C#) not be the equivalent of Friend (VBNET) when their respective definitions are: Friend VBNET The Friend (Visual Basic) keyword in the declaration statement specifies that the elements can be accessed from within the same assembly, but not from outside the assembly. [...] internal C# Internal: Access is limited to the current assembly. To my understanding, these definitions mean quite the same to me. Then, respectively, when I'm coding in VB.NET, I use the Friend keyword to specify that a class or a property shall be accessible only within the assembly where it is declared. The same in C#, I use the internal keyword to specify the same. Am I doing something or anything wrong from this perspective? What are the refinements I don't get? Might someone please explain how or in what Friend and internal are not direct equivalences? Thanks in advance for any of your answers!

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  • How do I return an array from a method?

    - by dwwilson66
    I'm trying to create a deck of cards for my homework. Code is posted below. I need to create four sets of cards (the four suits) and am create a multidimensional array. When I print the results instead of trying to pass the array, I can see that the data in the array is as expected. However, when I try to pass the array card, I get an error cannot find symbol. I've got this modeled after texbook and Java tutorial examples, and I need some help figuring out what I'm missing. I've over-documented to give an idea of how I'm thinking this SHOULD work...please let me know where I've gone horribly wrong in my understanding. import java.util.*; import java.lang.*; // public class CardGame { public static int[][] main(String[] args) { int[][] startDeck = deckOfCards(); /* cast new deck as int[][], calling method deckOfCards System.out.println(" /// from array: " + Arrays.deepToString(startDeck)); } public static int[][] deckOfCards() /* method to return a multi-dimensional array */ { int rank; int suit; for(rank=1;rank<14;rank++) /* cards 1 - 13 .... */ { for(suit=1;suit<5;suit++) /* suits 1 - 4 .... */ { int[][] card = new int[][] /* define a new card... */ { {rank,suit} /* with rank/suit from for... loops */ }; System.out.println(" /// from array: " + Arrays.deepToString(card)); } } return card; /* Error: cannot find symbol } }

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  • finding ALL cycles in a huge sparse matrix

    - by Andy
    Hi there, First of all I'm quite a Java beginner, so I'm not sure if this is even possible! Basically I have a huge (3+million) data source of relational data (i.e. A is friends with B+C+D, B is friends with D+G+Z (but not A - i.e. unmutual) etc.) and I want to find every cycle within this (not necessarily connected) directed graph. I've found this thread (http://stackoverflow.com/questions/546655/finding-all-cycles-in-graph/549402#549402) which has pointed me to Donald Johnson's (elementary) cycle-finding algorithm which, superficially at least, looks like it'll do what I'm after (I'm going to try when I'm back at work on Tuesday - thought it wouldn't hurt to ask in the meanwhile!). I had a quick scan through the code of the Java implementation of Johnson's algorithm (in that thread) and it looks like a matrix of relations is the first step, so I guess my questions are: a) Is Java capable of handling a 3+million*3+million matrix? (was planning on representing A-friends-with-B by a binary sparse matrix) b) Do I need to find every connected subgraph as my first problem, or will cycle-finding algorithms handle disjoint data? c) Is this actually an appropriate solution for the problem? My understanding of "elementary" cycles is that in the graph below, rather than picking out A-B-C-D-E-F it'll pick out A-B-F, B-C-D etc. but that's not the end of the world given the task. E / \ D---F / \ / \ C---B---A d) If necessary, I can simplify the problem by enforcing mutuality in relations - i.e. A-friends-with-B <== B-friends-with-A, and if really necessary I can maybe cut down the data size, but realistically it is always going to be around the 1mil mark. z) Is this a P or NP task?! Am I biting off more than I can chew? Thanks all, any help appreciated! Andy

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  • Efficient representation of Hierarchies in Hibernate.

    - by Alison G
    I'm having some trouble representing an object hierarchy in Hibernate. I've searched around, and haven't managed to find any examples doing this or similar - you have my apologies if this is a common question. I have two types which I'd like to persist using Hibernate: Groups and Items. * Groups are identified uniquely by a combination of their name and their parent. * The groups are arranged in a number of trees, such that every Group has zero or one parent Group. * Each Item can be a member of zero or more Groups. Ideally, I'd like a bi-directional relationship allowing me to get: * all Groups that an Item is a member of * all Items that are a member of a particular Group or its descendants. I also need to be able to traverse the Group tree from the top in order to display it on the UI. The basic object structure would ideally look like this: class Group { ... /** @return all items in this group and its descendants */ Set<Item> getAllItems() { ... } /** @return all direct children of this group */ Set<Group> getChildren() { ... } ... } class Item { ... /** @return all groups that this Item is a direct member of */ Set<Group> getGroups() { ... } ... } Originally, I had just made a simple bi-directional many-to-many relationship between Items and Groups, such that fetching all items in a group hierarchy required recursion down the tree, and fetching groups for an Item was a simple getter, i.e.: class Group { ... private Set<Item> items; private Set<Group> children; ... /** @return all items in this group and its descendants */ Set<Item> getAllItems() { Set<Item> allItems = new HashSet<Item>(); allItems.addAll(this.items); for(Group child : this.getChildren()) { allItems.addAll(child.getAllItems()); } return allItems; } /** @return all direct children of this group */ Set<Group> getChildren() { return this.children; } ... } class Item { ... private Set<Group> groups; /** @return all groups that this Item is a direct member of */ Set<Group> getGroups() { return this.groups; } ... } However, this resulted in multiple database requests to fetch the Items in a Group with many descendants, or for retrieving the entire Group tree to display in the UI. This seems very inefficient, especially with deeper, larger group trees. Is there a better or standard way of representing this relationship in Hibernate? Am I doing anything obviously wrong or stupid? My only other thought so far was this: Replace the group's id, parent and name fields with a unique "path" String which specifies the whole ancestry of a group, e.g.: /rootGroup /rootGroup/aChild /rootGroup/aChild/aGrandChild The join table between Groups and Items would then contain group_path and item_id. This immediately solves the two issues I was suffering previously: 1. The entire group hierarchy can be fetched from the database in a single query and reconstructed in-memory. 2. To retrieve all Items in a group or its descendants, we can select from group_item where group_path='N' or group_path like 'N/%' However, this seems to defeat the point of using Hibernate. All thoughts welcome!

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  • ASP.NET: How to get same validators control to be both client-side and server-side

    - by harrije
    Hello, For the ASP.NET validator controls, I want to use both client-side validation for the user experience and server-side validation to guard against hackers. ASP.NET documentation leads me to believe that if EnableClientScript="True" then there will be no server-side validation if client-side validation is possible for the user agent. To get server-side validation, the documentation says use EnableClientScript="False", which bypasses client-side validation altogether. Am I misunderstanding how the validator controls work? I ask because it seems obvious that many developers would want both client and server side validation together, and I find it hard to believe both together is not possible with one of the standard validation controls. If I am understanding the ASP.NET documentation correctly, then I can find only two options: Use two validator controls exactly the same except for their ID and EnableClientScript properties. Obviously ugly for maintaining two controls almost the same. Write some code behind to check if postback then invoke the Validate method on the validator group. Why write code behind if there a way to be automatic from the control? Is there a way to do so using a single validator control with no code behind? Thanks in advance for your input.

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  • IEnumerable.Cast not calling cast overload

    - by Martin Neal
    I'm not understanding something about the way .Cast works. I have an explicit (though implicit also fails) cast defined which seems to work when I use it "regularly", but not when I try to use .Cast. Why? Here is some compilable code that demonstrates my problem. public class Class1 { public string prop1 { get; set; } public int prop2 { get; set; } public static explicit operator Class2(Class1 c1) { return new Class2() { prop1 = c1.prop1, prop2 = c1.prop2 }; } } public class Class2 { public string prop1 { get; set; } public int prop2 { get; set; } } void Main() { Class1[] c1 = new Class1[] { new Class1() {prop1 = "asdf",prop2 = 1}}; //works Class2 c2 = (Class2)c1[0]; //doesn't work: Compiles, but throws at run-time //InvalidCastException: Unable to cast object of type 'Class1' to type 'Class2'. Class2 c3 = c1.Cast<Class2>().First(); }

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  • How memset initializes an array of integers by -1?

    - by haccks
    The manpage says about memset: #include <string.h> void *memset(void *s, int c, size_t n) The memset() function fills the first n bytes of the memory area pointed to by s with the constant byte c. It is clear that memset can't be used to initialize int array as shown below: int a[10]; memset(a, 1, sizeof(a)); it is because int is represented by 4 bytes (say) and one can not get the desired value for the integers in array a. But I often see the programmers use memset to set the int array elements to either 0 or -1. int a[10]; int b[10]; memset(a, 0, sizeof(a)); memset(b, -1, sizeof(b)); As per my understanding, initializing with integer 0 is OK because 0 can be represented in 1 byte (may be I am wrong in this context). But how it is possible to initialize b with -1 (a 4 bytes value)?

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  • Segmentation in Linux : Segmentation & Paging are redundant?

    - by claws
    Hello, I'm reading "Understanding Linux Kernel". This is the snippet that explains how Linux uses Segmentation which I didn't understand. Segmentation has been included in 80 x 86 microprocessors to encourage programmers to split their applications into logically related entities, such as subroutines or global and local data areas. However, Linux uses segmentation in a very limited way. In fact, segmentation and paging are somewhat redundant, because both can be used to separate the physical address spaces of processes: segmentation can assign a different linear address space to each process, while paging can map the same linear address space into different physical address spaces. Linux prefers paging to segmentation for the following reasons: Memory management is simpler when all processes use the same segment register values that is, when they share the same set of linear addresses. One of the design objectives of Linux is portability to a wide range of architectures; RISC architectures in particular have limited support for segmentation. All Linux processes running in User Mode use the same pair of segments to address instructions and data. These segments are called user code segment and user data segment , respectively. Similarly, all Linux processes running in Kernel Mode use the same pair of segments to address instructions and data: they are called kernel code segment and kernel data segment , respectively. Table 2-3 shows the values of the Segment Descriptor fields for these four crucial segments. I'm unable to understand 1st and last paragraph.

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  • What languages should a microISV use to write commercial software?

    - by Wal
    I've been writing software in Java for many years now, but it was always for internal applications that would be deployed to a server. I'd like to get into writing desktop applications now but I don't know where to start. I've written a few Java/Swing applications but again they were for internal use. My understanding is that Java and other semi-compiled and interpreted languages are too easy to reverse engineer, making them unsuitable for commercial software. I am aware that there are compilers for Java and some other interpreted language, but I've also heard that they are pricey and/or unreliable. Assuming I start a microISV and wish to develop and sell applications to a broad audience, what's my best bet? I would prefer something that can be written close to once, and compiled for different operating systems but I am not opposed to .NET and a Windows-only audience if other languages would compromise the experience (installation ease & user experience) in Windows. My only issue there is that I don't have a large starting budget and paying out the wazoo for the required development tools is not really in the cards.

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  • Fast sketching tools for drawing C/C++ structs, pointers, etc...

    - by tomasorti
    Hi. I would like to know what do you use to sketch relations between different entities in C/C++. This can be a very broad issue, so I'll try to clarify a bit more my question and give an example. I'm looking for something that is simple enough as a user, and let me sketch easily containers, pointers, etc... in an informal way. The aim is to document some structs relations to pass them to junior developers. A look at the drawings is supposed to accelerate the understanding of the code. My solutions at this moment are to use: 1) Paper & pencil. 2) Microsoft PowerPoint/Word Autoshapes. 3) Freeware Dia. Other ones could be: 4) Microsoft Visio, but my company does not own licenses. 5) UML tools. I don't want to go this way. This is what I mean a more formal solution. I know tools like Rational Rose are great, and I tried boUML and violet and they are fine in some parts, but I prefer the flexibility of options 2) or 3). Finally, let me write down a more concrete example: Let's say I what to sketch a map that contains another map as the mapped value, and that one contains a struct as the mapped value, that holds a vector of pointers of a type and a pointer to other type. Also, there exist other structs that hold pointers to the objects pointed by the previous map, so there are objects pointed from different places. This is just one example I have, but you can easily come with one from you experience. What would you use to sketch this example or another similar you have dealt with? Best regards, Tomas.

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  • Natural problems to solve using closures

    - by m.u.sheikh
    I have read quite a few articles on closures, and, embarassingly enough, I still don't understand this concept! Articles explain how to create a closure with a few examples, but I don't see any point in paying much attention to them, as they largely look contrived examples. I am not saying all of them are contrived, just that the ones I found looked contrived, and I dint see how even after understanding them, I will be able to use them. So in order to understand closures, I am looking at a few real problems, that can be solved very naturally using closures. For instance, a natural way to explain recursion to a person could be to explain the computation of n!. It is very natural to understand a problem like computing the factorial of a number using recursion. Similarly, it is almost a no-brainer to find an element in an unsorted array by reading each element, and comparing with the number in question. Also, at a different level, doing Object-oriented programming also makes sense. So I am trying to find a number of problems that could be solved with or without closures, but using closures makes thinking about them and solving them easier. Also, there are two types to closures, where each call to a closure can create a copy of the environment variables, or reference the same variables. So what sort of problems can be solved more naturally in which of the closure implementations?

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  • What is wrong with accessing DBI directly?

    - by canavanin
    Hi everyone! I'm currently reading Effective Perl Programming (2nd edition). I have come across a piece of code which was described as being poorly written, but I don't yet understand what's so bad about it, or how it should be improved. It would be great if someone could explain the matter to me. Here's the code in question: sub sum_values_per_key { my ( $class, $dsn, $user, $password, $parameters ) = @_; my %results; my $dbh = DBI->connect( $dsn, $user, $password, $parameters ); my $sth = $dbh->prepare( 'select key, calculate(value) from my_table'); $sth->execute(); # ... fill %results ... $sth->finish(); $dbh->disconnect(); return \%results; } The example comes from the chapter on testing your code (p. 324/325). The sentence that has left me wondering about how to improve the code is the following: Since the code was poorly written and accesses DBI directly, you'll have to create a fake DBI object to stand in for the real thing. I have probably not understood a lot of what the book has so far been trying to teach me, or I have skipped the section relevant for understanding what's bad practice about the above code... Well, thanks in advance for your help!

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  • How to retrieve the Description property from SettingsProperty?

    - by BadNinja
    For each item in my application's settings, I've added text to its Description Property which I want to retrieve at runtime. I'm sure I'm missing some basic logical nuance here, but everything I've tried has failed. Clearly, my understanding of what value needs to be passed to the Attributes property of the SettingsProperty class is wrong. I'm further confused by the fact that when I iterate through all they keys returned by SettingsProperty.Attributes.Keys, I can see "System.Configuration.SettingsDescriptionAttribute", but when I pass that string in as the key to the Attributes property, null is returned. Any insight into how to properly retrieve the value Description Property would be very much appreciated. Thanks. :) public void MyMethod() { SettingsPropertyCollection MyAppProperties = Properties.Settings.Default.Properties; IEnumerator enumerator = MyAppProperties.GetEnumerator(); // Iterate through all the keys to see what we have.... while (enumerator.MoveNext()) { SettingsProperty property = (SettingsProperty)enumerator.Current; ICollection myKeys = property.Attributes.Keys; foreach (object theKey in myKeys) System.Diagnostics.Debug.Print(theKey.ToString()); // One of the keys returned is: System.Configuration.SettingsDescriptionAttribute } enumerator.Reset(); while (enumerator.MoveNext()) { SettingsProperty property = (SettingsProperty)enumerator.Current; string propertyValue = property.DefaultValue.ToString(); // This fails: Null Reference string propertyDescription = property.Attributes["System.Configuration.SettingsDescriptionAttribute"].ToString(); // Do stuff with strings... } }

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  • Am I making the right choice in choosing Yii as my PHP Framework?

    - by Bara
    I am about to begin development of a new website and have been doing research on PHP Frameworks. I'm not an advanced PHP developer, but I have been developing web sites and apps (in asp.net) for a few years now. My website will primarily be AJAX-based (using jQuery) and making lots of calls to web services. After some research, here's what I came up with: CakePHP: Originally started developing in this, but found it too complex. The fact that it forces you to use and learn all this new stuff just to use it was a bit daunting, so I put it aside for the time being. Zend: The performance of the framework leaves me a bit skeptical, but I heard it has great support for creating web services. I also heard it was a bit complex. CodeIgniter: No real reason for not using this one. Based on what I've read CodeIgniter and Yii are very similar, but Yii is a bit faster and doesn't have un-needed code for PHP4 (since I plan on developing exclusively in PHP5). As far as Yii, the only things that scare me about it are that it is newer than the other frameworks so it has a smaller community. It also doesn't seem to have a ton of web service support (only SOAP, from my understanding) as opposed to Zend. So my questions come down to: Should these things worry me? (not as big of a community, poor web service support) Is there anything else I should look into? Is my choice of Yii over the other frameworks ok for a primarily AJAX-based web app? Bara

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  • 64-bit Alternative for Microsoft Jet

    - by David Robison
    Microsoft has chosen to not release a 64-bit version of Jet, their database driver for Access. Does anyone know of a good alternative? Here are the specific features that Jet supports that I need: Multiple users can connect to database over a network. Users can use Windows Explorer to copy the database while it is open without risking corruption. Access currently does this with enough reliability for what my customers need. Works well in C++ without requiring .Net. Alternatives I've considered that I do not think could work (though my understanding could be incorrect): SQLite: If multiple users connect to the database over a network, it will become corrupted. Firebird: Copying a database that is in use can corrupt the original database. SQL Server: Files in use are locked and cannot be copied. VistaDB: This appears to be .Net specific. Compile in 32-bit and use WOW64: There is another dependency that requires us to compile in 64-bit, even though we don't use any 64-bit functionality.

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  • Ideas Related to Subset Sum with 2,3 and more integers

    - by rolandbishop
    I've been struggling with this problem just like everyone else and I'm quite sure there has been more than enough posts to explain this problem. However in terms of understanding it fully, I wanted to share my thoughts and get more efficient solutions from all the great people in here related to Subset Sum problem. I've searched it over the Internet and there is actually a lot sources but I'm really willing to re-implement an algorithm or finding my own in order to understand fully. The key thing I'm struggling with is the efficiency considering the set size will be large. (I do not have a limit, just conceptually large). The two phases I'm trying to implement ideas on is finding two numbers that are equal to given integer T, finding three numbers and eventually K numbers. Some ideas I've though; For the two integer part I'm thing basically sorting the array O(nlogn) and for each element in the array searching for its negative value. (i.e if the array element is 3 searching for -3). Maybe a hash table inclusion could be better, providing a O(1) indexing the element? For the three or more integers I've found an amazing blog post;http://www.skorks.com/2011/02/algorithms-a-dropbox-challenge-and-dynamic-programming/. However even the author itself states that it is not applicable for large numbers. So I was for 2 and 3 and more integers what ideas could be applied for the subset problem. I'm struggling with setting up a dynamic programming method that will be efficient for the large inputs as well.

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