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• Design Pattern for Skipping Steps in a Wizard

  - by Eric J.

  I'm designing a flexible Wizard system that presents a number of screens to complete a task. Some screens may need to be skipped based on answers to prompts on one or more previous screens. The conditions to skip a given screen need to be editable by a non-technical user via a UI. Multiple conditions need only be combined with and. I have an initial design in mind, but it feels inelegant. I wonder if there's a better way to approach this class of problem. Initial Design UI where The first column allows the user to select a question from a previous screen. The second column allows the user to select an operator applicable to the type of question asked. The third column allows the user to enter one or more values depending on the selected operator. Object Model public enum Operations { ... } public class Condition { int QuestionId { get; set; } Operations Operation { get; set; } List<object> Parameters { get; private set; } } List<Condition> pageSkipConditions; Controller Logic bool allConditionsTrue = pageSkipConditions.Count > 0; foreach (Condition c in pageSkipConditions) { allConditionsTrue &= Evaluate(previousAnswers, c); } // ... private bool Evaluate(List<Answers> previousAnswers, Condition c) { switch (c.Operation) { case Operations.StartsWith: // logic for this operation // etc. } }

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• Creating a Predicate Builder extension method

  - by Rippo

  I have a Kendo UI Grid that I am currently allowing filtering on multiple columns. I am wondering if there is a an alternative approach removing the outer switch statement? Basically I want to able to create an extension method so I can filter on a IQueryable<T> and I want to drop the outer case statement so I don't have to switch column names. private static IQueryable<Contact> FilterContactList(FilterDescriptor filter, IQueryable<Contact> contactList) { switch (filter.Member) { case "Name": switch (filter.Operator) { case FilterOperator.StartsWith: contactList = contactList.Where(w => w.Firstname.StartsWith(filter.Value.ToString()) || w.Lastname.StartsWith(filter.Value.ToString()) || (w.Firstname + " " + w.Lastname).StartsWith(filter.Value.ToString())); break; case FilterOperator.Contains: contactList = contactList.Where(w => w.Firstname.Contains(filter.Value.ToString()) || w.Lastname.Contains(filter.Value.ToString()) || (w.Firstname + " " + w.Lastname).Contains( filter.Value.ToString())); break; case FilterOperator.IsEqualTo: contactList = contactList.Where(w => w.Firstname == filter.Value.ToString() || w.Lastname == filter.Value.ToString() || (w.Firstname + " " + w.Lastname) == filter.Value.ToString()); break; } break; case "Company": switch (filter.Operator) { case FilterOperator.StartsWith: contactList = contactList.Where(w => w.Company.StartsWith(filter.Value.ToString())); break; case FilterOperator.Contains: contactList = contactList.Where(w => w.Company.Contains(filter.Value.ToString())); break; case FilterOperator.IsEqualTo: contactList = contactList.Where(w => w.Company == filter.Value.ToString()); break; } break; } return contactList; } Some additional information, I am using NHibernate Linq. Also another problem is that the "Name" column on my grid is actually "Firstname" + " " + "LastName" on my contact entity. We can also assume that all filterable columns will be strings.

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• Why can't I assign a scalar value to a class using shorthand, but instead declare it first, then set

  - by ~delan-azabani

  I am writing a UTF-8 library for C++ as an exercise as this is my first real-world C++ code. So far, I've implemented concatenation, character indexing, parsing and encoding UTF-8 in a class called "ustring". It looks like it's working, but two (seemingly equivalent) ways of declaring a new ustring behave differently. The first way: ustring a; a = "test"; works, and the overloaded "=" operator parses the string into the class (which stores the Unicode strings as an dynamically allocated int pointer). However, the following does not work: ustring a = "test"; because I get the following error: test.cpp:4: error: conversion from ‘const char [5]’ to non-scalar type ‘ustring’ requested Is there a way to workaround this error? It probably is a problem with my code, though. The following is what I've written so far for the library: #include <cstdlib> #include <cstring> class ustring { int * values; long len; public: long length() { return len; } ustring * operator=(ustring input) { len = input.len; values = (int *) malloc(sizeof(int) * len); for (long i = 0; i < len; i++) values[i] = input.values[i]; return this; } ustring * operator=(char input[]) { len = sizeof(input); values = (int *) malloc(0); long s = 0; // s = number of parsed chars int a, b, c, d, contNeed = 0, cont = 0; for (long i = 0; i < sizeof(input); i++) if (input[i] < 0x80) { // ASCII, direct copy (00-7f) values = (int *) realloc(values, sizeof(int) * ++s); values[s - 1] = input[i]; } else if (input[i] < 0xc0) { // this is a continuation (80-bf) if (cont == contNeed) { // no need for continuation, use U+fffd values = (int *) realloc(values, sizeof(int) * ++s); values[s - 1] = 0xfffd; } cont = cont + 1; values[s - 1] = values[s - 1] | ((input[i] & 0x3f) << ((contNeed - cont) * 6)); if (cont == contNeed) cont = contNeed = 0; } else if (input[i] < 0xc2) { // invalid byte, use U+fffd (c0-c1) values = (int *) realloc(values, sizeof(int) * ++s); values[s - 1] = 0xfffd; } else if (input[i] < 0xe0) { // start of 2-byte sequence (c2-df) contNeed = 1; values = (int *) realloc(values, sizeof(int) * ++s); values[s - 1] = (input[i] & 0x1f) << 6; } else if (input[i] < 0xf0) { // start of 3-byte sequence (e0-ef) contNeed = 2; values = (int *) realloc(values, sizeof(int) * ++s); values[s - 1] = (input[i] & 0x0f) << 12; } else if (input[i] < 0xf5) { // start of 4-byte sequence (f0-f4) contNeed = 3; values = (int *) realloc(values, sizeof(int) * ++s); values[s - 1] = (input[i] & 0x07) << 18; } else { // restricted or invalid (f5-ff) values = (int *) realloc(values, sizeof(int) * ++s); values[s - 1] = 0xfffd; } return this; } ustring operator+(ustring input) { ustring result; result.len = len + input.len; result.values = (int *) malloc(sizeof(int) * result.len); for (long i = 0; i < len; i++) result.values[i] = values[i]; for (long i = 0; i < input.len; i++) result.values[i + len] = input.values[i]; return result; } ustring operator[](long index) { ustring result; result.len = 1; result.values = (int *) malloc(sizeof(int)); result.values[0] = values[index]; return result; } char * encode() { char * r = (char *) malloc(0); long s = 0; for (long i = 0; i < len; i++) { if (values[i] < 0x80) r = (char *) realloc(r, s + 1), r[s + 0] = char(values[i]), s += 1; else if (values[i] < 0x800) r = (char *) realloc(r, s + 2), r[s + 0] = char(values[i] >> 6 | 0x60), r[s + 1] = char(values[i] & 0x3f | 0x80), s += 2; else if (values[i] < 0x10000) r = (char *) realloc(r, s + 3), r[s + 0] = char(values[i] >> 12 | 0xe0), r[s + 1] = char(values[i] >> 6 & 0x3f | 0x80), r[s + 2] = char(values[i] & 0x3f | 0x80), s += 3; else r = (char *) realloc(r, s + 4), r[s + 0] = char(values[i] >> 18 | 0xf0), r[s + 1] = char(values[i] >> 12 & 0x3f | 0x80), r[s + 2] = char(values[i] >> 6 & 0x3f | 0x80), r[s + 3] = char(values[i] & 0x3f | 0x80), s += 4; } return r; } };

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• python: equivalent to Javascript "||" to override non-truthful value

  - by Jason S

  In Javascript I can do this: function A(x) { return x || 3; } This returns 3 if x is a "non-truthful" value like 0, null, false, and it returns x otherwise. This is useful for empty arguments, e.g. I can do A() and it will evaluate as 3. Does Python have an equivalent? I guess I could make one out of the ternary operator a if b else c but was wondering what people use for this.

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• Easiest way to calculate amount of even numbers in given range

  - by Fdr

  What is the simplest way to calculate the amount of even numbers in a range of unsigned integers? An example: if range is [0...4] then the answer is 3 (0,2,4) I'm having hard time to think of any simple way. The only solution I came up involved couple of if-statements. Is there a simple line of code that can do this without if-statements or ternary operators?

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• concurrency::accelerator

  - by Daniel Moth

  Overview An accelerator represents a "target" on which C++ AMP code can execute and where data can reside. Typically (but not necessarily) an accelerator is a GPU device. Accelerators are represented in C++ AMP as objects of the accelerator class. For many scenarios, you do not need to obtain an accelerator object, since the runtime has a notion of a default accelerator, which is what it thinks is the best one in the system. Examples where you need to deal with accelerator objects are if you need to pick your own accelerator (based on your specific criteria), or if you need to use more than one accelerators from your app. Construction and operator usage You can query and obtain a std::vector of all the accelerators on your system, which the runtime discovers on startup. Beyond enumerating accelerators, you can also create one directly by passing to the constructor a system-wide unique path to a device if you know it (i.e. the “Device Instance Path” property for the device in Device Manager), e.g. accelerator acc(L"PCI\\VEN_1002&DEV_6898&SUBSYS_0B001002etc"); There are some predefined strings (for predefined accelerators) that you can pass to the accelerator constructor (and there are corresponding constants for those on the accelerator class itself, so you don’t have to hardcode them every time). Examples are the following: accelerator::default_accelerator represents the default accelerator that the C++ AMP runtime picks for you if you don’t pick one (the heuristics of how it picks one will be covered in a future post). Example: accelerator acc; accelerator::direct3d_ref represents the reference rasterizer emulator that simulates a direct3d device on the CPU (in a very slow manner). This emulator is available on systems with Visual Studio installed and is useful for debugging. More on debugging in general in future posts. Example: accelerator acc(accelerator::direct3d_ref); accelerator::direct3d_warp represents a target that I will cover in future blog posts. Example: accelerator acc(accelerator::direct3d_warp); accelerator::cpu_accelerator represents the CPU. In this first release the only use of this accelerator is for using the staging arrays technique that I'll cover separately. Example: accelerator acc(accelerator::cpu_accelerator); You can also create an accelerator by shallow copying another accelerator instance (via the corresponding constructor) or simply assigning it to another accelerator instance (via the operator overloading of =). Speaking of operator overloading, you can also compare (for equality and inequality) two accelerator objects between them to determine if they refer to the same underlying device. Querying accelerator characteristics Given an accelerator object, you can access its description, version, device path, size of dedicated memory in KB, whether it is some kind of emulator, whether it has a display attached, whether it supports double precision, and whether it was created with the debugging layer enabled for extensive error reporting. Below is example code that accesses some of the properties; in your real code you'd probably be checking one or more of them in order to pick an accelerator (or check that the default one is good enough for your specific workload): void inspect_accelerator(concurrency::accelerator acc) { std::wcout << "New accelerator: " << acc.description << std::endl; std::wcout << "is_debug = " << acc.is_debug << std::endl; std::wcout << "is_emulated = " << acc.is_emulated << std::endl; std::wcout << "dedicated_memory = " << acc.dedicated_memory << std::endl; std::wcout << "device_path = " << acc.device_path << std::endl; std::wcout << "has_display = " << acc.has_display << std::endl; std::wcout << "version = " << (acc.version >> 16) << '.' << (acc.version & 0xFFFF) << std::endl; } accelerator_view In my next blog post I'll cover a related class: accelerator_view. Suffice to say here that each accelerator may have from 1..n related accelerator_view objects. You can get the accelerator_view from an accelerator via the default_view property, or create new ones by invoking the create_view method that creates an accelerator_view object for you (by also accepting a queuing_mode enum value of deferred or immediate that we'll also explore in the next blog post). Comments about this post by Daniel Moth welcome at the original blog.

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• concurrency::index<N> from amp.h

  - by Daniel Moth

  Overview C++ AMP introduces a new template class index<N>, where N can be any value greater than zero, that represents a unique point in N-dimensional space, e.g. if N=2 then an index<2> object represents a point in 2-dimensional space. This class is essentially a coordinate vector of N integers representing a position in space relative to the origin of that space. It is ordered from most-significant to least-significant (so, if the 2-dimensional space is rows and columns, the first component represents the rows). The underlying type is a signed 32-bit integer, and component values can be negative. The rank field returns N. Creating an index The default parameterless constructor returns an index with each dimension set to zero, e.g. index<3> idx; //represents point (0,0,0) An index can also be created from another index through the copy constructor or assignment, e.g. index<3> idx2(idx); //or index<3> idx2 = idx; To create an index representing something other than 0, you call its constructor as per the following 4-dimensional example: int temp[4] = {2,4,-2,0}; index<4> idx(temp); Note that there are convenience constructors (that don’t require an array argument) for creating index objects of rank 1, 2, and 3, since those are the most common dimensions used, e.g. index<1> idx(3); index<2> idx(3, 6); index<3> idx(3, 6, 12); Accessing the component values You can access each component using the familiar subscript operator, e.g. One-dimensional example: index<1> idx(4); int i = idx[0]; // i=4 Two-dimensional example: index<2> idx(4,5); int i = idx[0]; // i=4 int j = idx[1]; // j=5 Three-dimensional example: index<3> idx(4,5,6); int i = idx[0]; // i=4 int j = idx[1]; // j=5 int k = idx[2]; // k=6 Basic operations Once you have your multi-dimensional point represented in the index, you can now treat it as a single entity, including performing common operations between it and an integer (through operator overloading): -- (pre- and post- decrement), ++ (pre- and post- increment), %=, *=, /=, +=, -=,%, *, /, +, -. There are also operator overloads for operations between index objects, i.e. ==, !=, +=, -=, +, –. Here is an example (where no assertions are broken): index<2> idx_a; index<2> idx_b(0, 0); index<2> idx_c(6, 9); _ASSERT(idx_a.rank == 2); _ASSERT(idx_a == idx_b); _ASSERT(idx_a != idx_c); idx_a += 5; idx_a[1] += 3; idx_a++; _ASSERT(idx_a != idx_b); _ASSERT(idx_a == idx_c); idx_b = idx_b + 10; idx_b -= index<2>(4, 1); _ASSERT(idx_a == idx_b); Usage You'll most commonly use index<N> objects to index into data types that we'll cover in future posts (namely array and array_view). Also when we look at the new parallel_for_each function we'll see that an index<N> object is the single parameter to the lambda, representing the (multi-dimensional) thread index… In the next post we'll go beyond being able to represent an N-dimensional point in space, and we'll see how to define the N-dimensional space itself through the extent<N> class. Comments about this post by Daniel Moth welcome at the original blog.

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• How to get distinct values from the List&lt;T&gt; with LINQ

  - by Vincent Maverick Durano

  Recently I was working with data from a generic List<T> and one of my objectives is to get the distinct values that is found in the List. Consider that we have this simple class that holds the following properties: public class Product { public string Make { get; set; } public string Model { get; set; } }   Now in the page code behind we will create a list of product by doing the following: private List<Product> GetProducts() { List<Product> products = new List<Product>(); Product p = new Product(); p.Make = "Samsung"; p.Model = "Galaxy S 1"; products.Add(p); p = new Product(); p.Make = "Samsung"; p.Model = "Galaxy S 2"; products.Add(p); p = new Product(); p.Make = "Samsung"; p.Model = "Galaxy Note"; products.Add(p); p = new Product(); p.Make = "Apple"; p.Model = "iPhone 4"; products.Add(p); p = new Product(); p.Make = "Apple"; p.Model = "iPhone 4s"; products.Add(p); p = new Product(); p.Make = "HTC"; p.Model = "Sensation"; products.Add(p); p = new Product(); p.Make = "HTC"; p.Model = "Desire"; products.Add(p); p = new Product(); p.Make = "Nokia"; p.Model = "Some Model"; products.Add(p); p = new Product(); p.Make = "Nokia"; p.Model = "Some Model"; products.Add(p); p = new Product(); p.Make = "Sony Ericsson"; p.Model = "800i"; products.Add(p); p = new Product(); p.Make = "Sony Ericsson"; p.Model = "800i"; products.Add(p); return products; }   And then let’s bind the products to the GridView. protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { Gridview1.DataSource = GetProducts(); Gridview1.DataBind(); } }   Running the code will display something like this in the page: Now what I want is to get the distinct row values from the list. So what I did is to use the LINQ Distinct operator and unfortunately it doesn't work. In order for it work is you must use the overload method of the Distinct operator for you to get the desired results. So I’ve added this IEqualityComparer<T> class to compare values: class ProductComparer : IEqualityComparer<Product> { public bool Equals(Product x, Product y) { if (Object.ReferenceEquals(x, y)) return true; if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null)) return false; return x.Make == y.Make && x.Model == y.Model; } public int GetHashCode(Product product) { if (Object.ReferenceEquals(product, null)) return 0; int hashProductName = product.Make == null ? 0 : product.Make.GetHashCode(); int hashProductCode = product.Model.GetHashCode(); return hashProductName ^ hashProductCode; } }   After that you can then bind the GridView like this: protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { Gridview1.DataSource = GetProducts().Distinct(new ProductComparer()); Gridview1.DataBind(); } }   Running the page will give you the desired output below: As you notice, it now eliminates the duplicate rows in the GridView. Now what if we only want to get the distinct values for a certain field. For example I want to get the distinct “Make” values such as Samsung, Apple, HTC, Nokia and Sony Ericsson and populate them to a DropDownList control for filtering purposes. I was hoping the the Distinct operator has an overload that can compare values based on the property value like (GetProducts().Distinct(o => o.PropertyToCompare). But unfortunately it doesn’t provide that overload so what I did as a workaround is to use the GroupBy,Select and First LINQ query operators to achieve what I want. Here’s the code to get the distinct values of a certain field. protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { DropDownList1.DataSource = GetProducts().GroupBy(o => o.Make).Select(o => o.First()); DropDownList1.DataTextField = "Make"; DropDownList1.DataValueField = "Model"; DropDownList1.DataBind(); } } Running the code will display the following output below:   That’s it! I hope someone find this post useful!

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• Sort list using stl sort function

  - by Vlad

  I'm trying to sort a list (part of a class) in descending containg items of a struct but it doesn't compile(error: no match for 'operator-' in '__last - __first'): sort(Result.poly.begin(), Result.poly.end(), SortDescending()); And here's SortDescending: struct SortDescending { bool operator()(const term& t1, const term& t2) { return t2.pow < t1.pow; } }; Can anyone tell me what's wrong? Thanks!

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• DotNetOpenAuth: Mock ClaimsResponse

  - by Pickels

  Hello, I was wondering how I can mock the ClaimseReponse class in DotNetOpenAuth? This is the class(remove a few properties): [Serializable] public sealed class ClaimsResponse : ExtensionBase, IClientScriptExtensionResponse, IExtensionMessage, IMessageWithEvents, IMessage { public static bool operator !=(ClaimsResponse one, ClaimsResponse other); public static bool operator ==(ClaimsResponse one, ClaimsResponse other); [MessagePart("email")] public string Email { get; set; } [MessagePart("fullname")] public string FullName { get; set; } public override bool Equals(object obj); public override int GetHashCode(); } This is what I tried: ClaimsResponse MockCR = new ClaimsResponse(); MockCR.Email = "[email protected]"; MockCR.FullName = "Mister T"; I get the following error: '...ClaimsResponse(string)' is inaccessible due to its protection level. Kind regards, Pickels

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• C++ Why is the converter constructor implicitly called?

  - by ShaChris23

  Why is the Child class's converter constructor called in the code below? I mean, it automatically converts Base to Child via the Child converter constructor. The code below compiles, but shouldn't it not compile since I haven't provided bool Child::operator!=(Base const&)? class Base { }; class Child : public Base { public: Child() {} Child(Base const& base_) : Base(base_) { std::cout <<"should never called!"; } bool operator!=(Child const&) { return true; } }; void main() { Base base; Child child; if(child != base) std::cout << "not equal"; else std::cout << "equal"; }

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• How to read verbose VC++ linker output

  - by Assaf Lavie

  Trying to debug some linker errors, I turned on /VERBOSE and I'm trying to make sense of the output. It occurs to me that I really don't know how to read it. For example: 1>Compiling version info 1>Linking... 1>Starting pass 1 1>Processed /DEFAULTLIB:mfc80.lib 1>Processed /DEFAULTLIB:mfcs80.lib 1>Processed /DEFAULTLIB:msvcrt.lib 1>Processed /DEFAULTLIB:kernel32.lib 1>Processed /DEFAULTLIB:user32.lib .... 1>Processed /DEFAULTLIB:libgslcblasMD.lib 1>Searching libraries 1> Searching V:\Src\Solutions\\..\..\\Common\Win32\Lib\PlxApi.lib: 1> Searching ..\..\..\..\out\win32\release\lib\camerageometry.lib: 1> Searching ..\..\..\..\out\win32\release\lib\geometry.lib: 1> Found "public: __thiscall VisionMap::Geometry::Box2d::operator class VisionMap::Geometry::Box2DInt(void)const " (??BBox2d@Geometry@VisionMap@@QBE?AVBox2DInt@12@XZ) 1> Referenced in FocusDlg.obj 1> Loaded geometry.lib(Box2d.obj) 1>Processed /DEFAULTLIB:CGAL-vc80-mt.lib 1>Processed /DEFAULTLIB:boost_thread-vc80-mt-1_33_1.lib What's going on here? I think I understand this bit: 1>Processed /DEFAULTLIB:libgslcblasMD.lib 1>Searching libraries 1> Searching V:\Src\Solutions\\..\..\\Common\Win32\Lib\PlxApi.lib: 1> Searching ..\..\..\..\out\win32\release\lib\camerageometry.lib: 1> Searching ..\..\..\..\out\win32\release\lib\geometry.lib: 1> Found "public: __thiscall VisionMap::Geometry::Box2d::operator class VisionMap::Geometry::Box2DInt(void)const " (??BBox2d@Geometry@VisionMap@@QBE?AVBox2DInt@12@XZ) 1> Referenced in FocusDlg.obj 1> Loaded geometry.lib(Box2d.obj) It's trying to find the implementation of the above operator, which is used somewhere in FocusDlg.cpp, and it finds it in geometry.lib. But what does 1>Processed /DEFAULTLIB:libgslcblasMD.lib mean? What determines the order of symbol resolution? Why is it loading this particular symbol while processing libgslcblasMD.lib which is a 3rd party library? Or am I reading it wrong? It seems that the linker is going through the symbols referenced in the project's various object files, but I have no idea in what order. It then searches the static libraries the project uses - by project reference, explicit import and automatic default library imports; but it does so in an order that, again, seems arbitrary to me. When it finds a symbol, for example in geometry.lib, it then continues to find a bunch of other symbols from the same lib: 1> Searching V:\Src\Solutions\\..\..\\Common\Win32\Lib\PlxApi.lib: 1> Searching ..\..\..\..\out\win32\release\lib\camerageometry.lib: 1> Searching ..\..\..\..\out\win32\release\lib\geometry.lib: 1> Found "public: __thiscall VisionMap::Geometry::Box2d::operator class VisionMap::Geometry::Box2DInt(void)const " (??BBox2d@Geometry@VisionMap@@QBE?AVBox2DInt@12@XZ) 1> Referenced in FocusDlg.obj 1> Loaded geometry.lib(Box2d.obj) 1>Processed /DEFAULTLIB:CGAL-vc80-mt.lib 1>Processed /DEFAULTLIB:boost_thread-vc80-mt-1_33_1.lib 1> Found "public: __thiscall VisionMap::Geometry::Box2DInt::Box2DInt(int,int,int,int)" (??0Box2DInt@Geometry@VisionMap@@QAE@HHHH@Z) 1> Referenced in FocusDlg.obj 1> Referenced in ImageView.obj 1> Referenced in geometry.lib(Box2d.obj) 1> Loaded geometry.lib(Box2DInt.obj) 1> Found "public: virtual __thiscall VisionMap::Geometry::Point3d::~Point3d(void)" (??1Point3d@Geometry@VisionMap@@UAE@XZ) 1> Referenced in GPSFrm.obj 1> Referenced in MainFrm.obj 1> Loaded geometry.lib(Point3d.obj) 1> Found "void __cdecl VisionMap::Geometry::serialize<class boost::archive::binary_oarchive>(class boost::archive::binary_oarchive &,class VisionMap::Geometry::Point3d &,unsigned int)" (??$serialize@Vbinary_oarchive@archive@boost@@@Geometry@VisionMap@@YAXAAVbinary_oarchive@archive@boost@@AAVPoint3d@01@I@Z) 1> Referenced in GPSFrm.obj 1> Referenced in MainFrm.obj 1> Loaded geometry.lib(GeometrySerializationImpl.obj) But then, for some reason, it goes on to find symbols that are defined in other libs, and returns to geometry later on (a bunch of times). So clearly it's not doing "look in geometry and load every symbol that's references in the project, and then continue to other libraries". But it's not clear to me what is the order of symbol lookup. And what's the deal with all those libraries being processed at the beginning of the linker's work, but not finding any symbols to load from them? Does this project really not use anything from msvcrt.lib, kernel32.lib? Seems unlikely. So basically I'm looking to decipher the underlying order in the linker's operation.

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• Boost bind function

  - by Gokul

  Hi, I have a abstract base class A and a set of 10 derived classes. The infix operator is overloaded in all of the derived classes class A{ void printNode( std::ostream& os ) { this->printNode_p(); } void printNode_p( std::ostream& os ) { os << (*this); } }; There is a container which stores the base class pointers. I want to use boost::bind function to call the overloaded infix operator in each of its derived class. I have written like this std::vector<A*> m_args .... std::ostream os; for_each( m_args.begin(), m_args.end(), bind(&A::printNode, _1, os) ); What is the problem with this code? Thanks, Gokul.

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• Enumerate shared folders on Windows with low privileges

  - by Phil Nash

  Using C++ (VS2008) I need to be able to enumerate all shared folders on the current machine and get or construct the local and remote names. We've been using NetShareEnum for this fairly successfully, but have hit a problem where we need to run with a user account with low privileges. To get the local path using NetShareEnum we need to retrieve at least SHARE_INFO_2 structures - but that requires "Administrator, Power User, Print Operator, or Server Operator group membership". I've been trying to use WNetOpenEnum and WNetEnumResource instead but I don't seem to be getting the local name back for that for shares either - and I can't seem to get it to enumerate just local resources - it goes off and finds all shared resources on the local network - which is not an acceptable overhead. So I'd either like help on where I'm going wrong with WNetEnumResource, or a suggestion as to another way of doing this. Any suggestions are much appreciated.

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• Is this an F# quotations bug?

  - by ControlFlow

  [<ReflectedDefinition>] let rec x = (fun() -> x + "abc") () The sample code with the recursive value above produces the following F# compiler error: error FS0432: [<ReflectedDefinition>] terms cannot contain uses of the prefix splice operator '%' I can't see any slicing operator usage in the code above, looks like a bug... :) Looks like this is the problem with the quotation via ReflectedDefinitionAttribute only, normal quotation works well: let quotation = <@ let rec x = (fun() -> x + "abc") () in x @> produces expected result with the hidden Lazy.create and Lazy.force usages: val quotation : Quotations.Expr<string> = LetRecursive ([(x, Lambda (unitVar, Application (Lambda (unitVar0, Call (None, String op_Addition[String,String,String](String, String), [Call (None, String Force[String](Lazy`1[System.String]), [x]), Value ("abc")])), Value (<null>)))), (x, Call (None, Lazy`1[String] Create[String](FSharpFunc`2[Unit,String]), [x])), (x, Call (None, String Force[String](Lazy`1[String]), [x]))], x) So the question is: is this an F# compiler bug or not?

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• postgres - ERROR: syntax error at or near "COST"

  - by cino21122

  EDIT Taking COST 100 out made the command go through, however, I'm still unable to run my query because it yields this error: ERROR: function group_concat(character) does not exist HINT: No function matches the given name and argument types. You may need to add explicit type casts. The query I'm running is this: select tpid, group_concat(z) as z, group_concat(cast(r as char(2))) as r, group_concat(to_char(datecreated,'DD-Mon-YYYY HH12:MI am')) as datecreated, group_concat(to_char(datemodified,'DD-Mon-YYYY HH12:MI am')) as datemodified from tpids group by tpid order by tpid, zip This function seems to work fine locally, but moving it online yields this error... Is there something I'm missing? CREATE OR REPLACE FUNCTION group_concat(text, text) RETURNS text AS $BODY$ SELECT CASE WHEN $2 IS NULL THEN $1 WHEN $1 IS NULL THEN $2 ELSE $1 operator(pg_catalog.||) ',' operator(pg_catalog.||) $2 END $BODY$ LANGUAGE 'sql' IMMUTABLE COST 100; ALTER FUNCTION group_concat(text, text) OWNER TO j76dd3;

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• What Causes Boost Asio to Crash Like This?

  - by Scott Lawson

  My program appears to run just fine most of the time, but occasionally I get a segmentation fault. boost version = 1.41.0 running on RHEL 4 compiled with GCC 3.4.6 Backtrace: #0 0x08138546 in boost::asio::detail::posix_fd_set_adapter::is_set (this=0xb74ed020, descriptor=-1) at /home/scottl/boost_1_41_0/boost/asio/detail/posix_fd_set_adapter.hpp:57 __result = -1 'ÿ' #1 0x0813e1b0 in boost::asio::detail::reactor_op_queue::perform_operations_for_descriptors (this=0x97f3b6c, descriptors=@0xb74ed020, result=@0xb74ecec8) at /home/scottl/boost_1_41_0/boost/asio/detail/reactor_op_queue.hpp:204 op_iter = {_M_node = 0xb4169aa0} i = {_M_node = 0x97f3b74} #2 0x081382ca in boost::asio::detail::select_reactor::run (this=0x97f3b08, block=true) at /home/scottl/boost_1_41_0/boost/asio/detail/select_reactor.hpp:388 read_fds = {fd_set_ = {fds_bits = {16, 0 }}, max_descriptor_ = 65} write_fds = {fd_set_ = {fds_bits = {0 }}, max_descriptor_ = -1} retval = 1 lock = { = {}, mutex_ = @0x97f3b1c, locked_ = true} except_fds = {fd_set_ = {fds_bits = {0 }}, max_descriptor_ = -1} max_fd = 65 tv_buf = {tv_sec = 0, tv_usec = 710000} tv = (timeval *) 0xb74ecf88 ec = {m_val = 0, m_cat = 0x81f2c24} sb = { = {}, blocked_ = true, old_mask_ = {__val = {0, 0, 134590223, 3075395548, 3075395548, 3075395464, 134729792, 3075395360, 135890240, 3075395368, 134593920, 3075395544, 135890240, 3075395384, 134599542, 3020998404, 135890240, 3075395400, 134614095, 3075395544, 4, 3075395416, 134548135, 3021172996, 4294967295, 3075395432, 134692921, 3075395504, 0, 3075395448, 134548107, 3021172992}}} #3 0x0812eb45 in boost::asio::detail::task_io_service ::do_one (this=0x97f3a70, lock=@0xb74ed230, this_idle_thread=0xb74ed240, ec=@0xb74ed2c0) at /home/scottl/boost_1_41_0/boost/asio/detail/task_io_service.hpp:260 more_handlers = false c = {lock_ = @0xb74ed230, task_io_service_ = @0x97f3a70} h = (boost::asio::detail::handler_queue::handler *) 0x97f3aa0 polling = false task_has_run = true #4 0x0812765f in boost::asio::detail::task_io_service ::run (this=0x97f3a70, ec=@0xb74ed2c0) at /home/scottl/boost_1_41_0/boost/asio/detail/task_io_service.hpp:103 ctx = { = {}, owner_ = 0x97f3a70, next_ = 0x0} this_idle_thread = {wakeup_event = { = {}, cond_ = {__c_lock = { __status = 0, __spinlock = 22446}, __c_waiting = 0x2bd7, __padding = "\000\000\000\000×+\000\000\000\000\000\000×+\000\000\000\000\000\000\204:\177\t\000\000\000", __align = 0}, signalled_ = true}, next = 0x0} lock = { = {}, mutex_ = @0x97f3a84, locked_ = false} n = 11420 #5 0x08125e99 in boost::asio::io_service::run (this=0x97ebbcc) at /home/scottl/boost_1_41_0/boost/asio/impl/io_service.ipp:58 ec = {m_val = 0, m_cat = 0x81f2c24} s = 8 #6 0x08154424 in boost::_mfi::mf0::operator() (this=0x9800870, p=0x97ebbcc) at /home/scottl/boost_1_41_0/boost/bind/mem_fn_template.hpp:49 No locals. #7 0x08154331 in boost::_bi::list1 ::operator(), boost::_bi::list0 (this=0x9800878, f=@0x9800870, a=@0xb74ed337) at /home/scottl/boost_1_41_0/boost/bind/bind.hpp:236 No locals. #8 0x081541e5 in boost::_bi::bind_t, boost::_bi::list1 ::operator() (this=0x9800870) at /home/scottl/boost_1_41_0/boost/bind/bind_template.hpp:20 a = {} #9 0x08154075 in boost::detail::thread_data, boost::_bi::list1 ::run (this=0x98007a0) at /home/scottl/boost_1_41_0/boost/thread/detail/thread.hpp:56 No locals. #10 0x0816fefd in thread_proxy () at /usr/lib/gcc/i386-redhat-linux/3.4.6/../../../../include/c++/3.4.6/bits/locale_facets.tcc:2443 __ioinit = {static _S_refcount = , static _S_synced_with_stdio = } ---Type to continue, or q to quit--- typeinfo for common::RuntimeException = {} typeinfo name for common::RuntimeException = "N6common16RuntimeExceptionE" #11 0x00af23cc in start_thread () from /lib/tls/libpthread.so.0 No symbol table info available. #12 0x00a5c96e in __init_misc () from /lib/tls/libc.so.6 No symbol table info available.

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• Using string constants in implicit conversion

  - by kornelijepetak

  Consider the following code: public class TextType { public TextType(String text) { underlyingString = text; } public static implicit operator String(TextType text) { return text.underlyingString; } private String underlyingString; } TextType text = new TextType("Something"); String str = text; // This is OK. But I want to be able do the following, if possible. TextType textFromStringConstant = "SomeOtherText"; I can't extend the String class with the TextType implicit operator overload, but is there any way to assign a literal string to another class (which is handled by a method or something)? String is a reference type so when they developed C# they obviously had to use some way to get a string literal to the class. I just hope it's not hardcoded into the language.

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• Nonstandard SSIS lookup

  - by Stefan

  I have a situation where I am trying to lookup a value in one table based on values in another table, using a BETWEEN operator and not an = operator. In one table, I have a value "EffectiveDate". I want to get a Weight number from another table, but the other table has two fields: "Inception" and "Termination". What I want to do is extract the Weight from that table for use where the EffectiveDate is between Inception and Termination. SSIS doesn't seem to provide a way to do this. It's good at matching one column to another column, but doesn't seem to allow one to many-column comparison/operations. Am I missing anything? Is this possible to do somehow?

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• python: iif or (x ? a : b)

  - by Albert

  If Python would support the (x ? a : b) syntax from C/C++, I would write: print paid ? ("paid: " + str(paid) + " €") : "not paid" I really don't want to have an if-check and two independent prints here (because that is only an example above, in my code, it looks much more complicated and would really be stupid to have almost the same code twice). However, Python does not support this operator or any similar operator (afaik). What is the easiest/cleanest/most common way to do this? I have searched a bit and seen someone defining an iif(cond,iftrue,iffalse) function, inspired from Visual Basic. I wondered if I really have to add that code and if/why there is no such basic function in the standard library.

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• Creating an AST node in Erlang

  - by dagda1

  Hi, I am playing about with Erlang and I am trying to write a simple arithmetic parser. I want to try and parse the following expression: ((12+3)-4) I want to parse the expression into a stack of AST nodes. When parsing this expression, I would first of all create a binary expression for the (12+3) expression which would look something like this in C#: var binaryStructure = new BinaryStructure(); binaryStructure.Left = IntegerLiteralExpression(12); binaryStructure.Right = IntegerLiteralExpression(4); binaryStructure.Operator = binaryExpression.Operator != BinaryOperatorType.Addition; I am quite new to Erlang and I am wondering how I would go about creating a structure like this in Erlang that I can place on a List that I would use as the stack of expressions. Can anyone suggest how to create such a tree like structure? Would a function be a good fit? Thanks Paul

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• May volatile be in user defined types to help writing thread-safe code

  - by David Rodríguez - dribeas

  I know, it has been made quite clear in a couple of questions/answers before, that volatile is related to the visible state of the c++ memory model and not to multithreading. On the other hand, this article by Alexandrescu uses the volatile keyword not as a runtime feature but rather as a compile time check to force the compiler into failing to accept code that could be not thread safe. In the article the keyword is used more like a required_thread_safety tag than the actual intended use of volatile. Is this (ab)use of volatile appropriate? What possible gotchas may be hidden in the approach? The first thing that comes to mind is added confusion: volatile is not related to thread safety, but by lack of a better tool I could accept it. Basic simplification of the article: If you declare a variable volatile, only volatile member methods can be called on it, so the compiler will block calling code to other methods. Declaring an std::vector instance as volatile will block all uses of the class. Adding a wrapper in the shape of a locking pointer that performs a const_cast to release the volatile requirement, any access through the locking pointer will be allowed. Stealing from the article: template <typename T> class LockingPtr { public: // Constructors/destructors LockingPtr(volatile T& obj, Mutex& mtx) : pObj_(const_cast<T*>(&obj)), pMtx_(&mtx) { mtx.Lock(); } ~LockingPtr() { pMtx_->Unlock(); } // Pointer behavior T& operator*() { return *pObj_; } T* operator->() { return pObj_; } private: T* pObj_; Mutex* pMtx_; LockingPtr(const LockingPtr&); LockingPtr& operator=(const LockingPtr&); }; class SyncBuf { public: void Thread1() { LockingPtr<BufT> lpBuf(buffer_, mtx_); BufT::iterator i = lpBuf->begin(); for (; i != lpBuf->end(); ++i) { // ... use *i ... } } void Thread2(); private: typedef vector<char> BufT; volatile BufT buffer_; Mutex mtx_; // controls access to buffer_ };

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• How Do I Loop Through a Date Range in Reverse?

  - by Russ Bradberry

  I have a date range that I would like to be able to loop through in reverse. Give the following, how would I accomplish this, the standard Range operator doesn't seem t be working properly. >> sd = Date.parse('2010-03-01') => Mon, 01 Mar 2010 >> ed = Date.parse('2010-03-05') => Fri, 05 Mar 2010 >> (sd..ed).to_a => [Mon, 01 Mar 2010, Tue, 02 Mar 2010, Wed, 03 Mar 2010, Thu, 04 Mar 2010, Fri, 05 Mar 2010] >> (ed..sd).to_a => [] as you can see, the range operator works properly form start to end, but not from end to start.

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• Passing const CName as this argument discards qualifiers

  - by Geno Diaz

  I'm having trouble with passing a constant class through a function. // test the constructors auto CName nameOne("Robert", "Bresson"); const CName nameTwo = nameOne; auto CName nameThree; // display the contents of each newly-constructed object... // should see "Robert Bresson" cout << "nameOne = "; nameOne.WriteFullName(); cout << endl; // should see "Robert Bresson" again cout << "nameTwo = "; nameTwo.WriteFullName(); cout << endl; As soon as the compiler hits nameTwo.WriteFullName() I get the error of abandoning qualifiers. I know that the class is a constant however I can't figure out how to work around it. The function is in a header file written as so: void const WriteFullName(ostream& outstream = cout) { outstream << m_first << ' ' << m_last; } I receive this error when const is put in back of the function header main.cpp:(.text+0x51): undefined reference to CName::CName()' main.cpp:(.text+0x7c): undefined reference toCName::WriteFullName(std::basic_ostream &) const' main.cpp:(.text+0xbb): undefined reference to CName::WriteFullName(std::basic_ostream<char, std::char_traits<char> >&) const' main.cpp:(.text+0xf7): undefined reference toCName::WriteFullName(std::basic_ostream &) const' main.cpp:(.text+0x133): undefined reference to operator>>(std::basic_istream<char, std::char_traits<char> >&, CName&)' main.cpp:(.text+0x157): undefined reference tooperator<<(std::basic_ostream &, CName const&)' main.cpp:(.text+0x1f4): undefined reference to operator<<(std::basic_ostream<char, std::char_traits<char> >&, CName const&)' main.cpp:(.text+0x22b): undefined reference tooperator<<(std::basic_ostream &, CName const&)' main.cpp:(.text+0x25f): undefined reference to operator<<(std::basic_ostream<char, std::char_traits<char> >&, CName const&)' main.cpp:(.text+0x320): undefined reference tooperator<<(std::basic_ostream &, CName const&)' main.cpp:(.text+0x347): undefined reference to `operator(std::basic_istream &, CName&)'

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• Accessing structure elements using pointers

  - by Arun Nadesh

  Hi Everybody, Greetings! I got surprised when the following program did not crash. typedef struct _x{ int a; char b; int c; }x; main() { x *ptr=0; char *d=&ptr->b; } As per my understanding the -> operator has higher precedence over & operator. So I expected the program to crash at the below statement when we try to dereference the NULL pointer tr. char *d=&ptr->b; But the statement &ptr->b evaluates to a valid address. Could somebody please explain where I'm wrong? Thanks & Regards, Arun

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