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  • How to make that the LanguageBinder take precedence over the DynamicBinder

    - by rudimenter
    Hi I Have a class which implement IDynamicMetaObjectProvider I implement the BindGetMember Method from DynamicMetaObject. Now when i Generate a dynamic Object and Access a property every call gets implicit passed through the BindGetMember Method. I want that at first the language Binder get his chance before my code comes in. It is somehow doable with "binder.FallbackGetMember" but i am not sure how the expression has to look like. I call here dynamic com=CommandFactory.GetCommand(); com.testprop; //expected: "test"; but "test2" comes back public class Command : System.Dynamic.IDynamicMetaObjectProvider { public string testprop { get { return "test"; } } public object GetValue(string name) { return "test2"; } System.Dynamic.DynamicMetaObject System.Dynamic.IDynamicMetaObjectProvider.GetMetaObject(System.Linq.Expressions.Expression parameter) { return new MetaCommand(parameter, this); } private class MetaCommand : System.Dynamic.DynamicMetaObject { public MetaCommand(Expression expression, Command value) : base(expression, System.Dynamic.BindingRestrictions.Empty, value) { } public override System.Dynamic.DynamicMetaObject BindGetMember(System.Dynamic.GetMemberBinder binder) { var self = this.Expression; var bag = (Command)base.Value; Expression target; target = Expression.Call( Expression.Convert(self, typeof(Command)), typeof(Command).GetMethod("GetValue"), Expression.Constant(binder.Name) ); var restrictions = BindingRestrictions .GetInstanceRestriction(self, bag); return new DynamicMetaObject(target, restrictions); } #endregion } }

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  • Getting a handle on GIS math, where do I start?

    - by Joshua
    I am in charge of a program that is used to create a set of nodes and paths for consumption by an autonomous ground vehicle. The program keeps track of the locations of all items in its map by indicating the item's position as being x meters north and y meters east of an origin point of 0,0. In the real world, the vehicle knows the location of the origin's lat and long, as it is determined by a dgps system and is accurate down to a couple centimeters. My program is ignorant of any lat long coordinates. It is one of my goals to modify the program to keep track of lat long coords of items in addition to an origin point and items' x,y position in relation to that origin. At first blush, it seems that I am going to modify the program to allow the lat long coords of the origin to be passed in, and after that I desire that the program will automatically calculate the lat long of every item currently in a map. From what I've researched so far, I believe that I will need to figure out the math behind converting to lat long coords from a UTM like projection where I specify the origin points and meridians etc as opposed to whatever is defined already for UTM. I've come to ask of you GIS programmers, am I on the right track? It seems to me like there is so much to wrap ones head around, and I'm not sure if the answer isn't something as simple as, "oh yea theres a conversion from meters to lat long, here" Currently, due to the nature of DGPS, the system really doesn't need to care about locations more than oh, what... 40 km? radius away from the origin. Given this, and the fact that I need to make sure that the error on my coordinates is not greater than .5 meters, do I need anything more complex than a simple lat/long to meters conversion constant? I'm knee deep in materials here. I could use some pointers about what concepts to research. Thanks much!

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  • How can I pass a const array or a variable array to a function in C?

    - by CSharperWithJava
    I have a simple function Bar that uses a set of values from a data set that is passed in in the form of an Array of data structures. The data can come from two sources: a constant initialized array of default values, or a dynamically updated cache. The calling function determines which data is used and should be passed to Bar. Bar doesn't need to edit any of the data and in fact should never do so. How should I declare Bar's data parameter so that I can provide data from either set? union Foo { long _long; int _int; } static const Foo DEFAULTS[8] = {1,10,100,1000,10000,100000,1000000,10000000}; static Foo Cache[8] = {0}; void Bar(Foo* dataSet, int len);//example function prototype Note, this is C, NOT C++ if that makes a difference; Edit Oh, one more thing. When I use the example prototype I get a type qualifier mismatch warning, (because I'm passing a mutable reference to a const array?). What do I have to change for that?

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  • C++ Switch won't compile with externally defined variable used as case

    - by C Nielsen
    I'm writing C++ using the MinGW GNU compiler and the problem occurs when I try to use an externally defined integer variable as a case in a switch statement. I get the following compiler error: "case label does not reduce to an integer constant". Because I've defined the integer variable as extern I believe that it should compile, does anyone know what the problem may be? Below is an example: test.cpp #include <iostream> #include "x_def.h" int main() { std::cout << "Main Entered" << std::endl; switch(0) { case test_int: std::cout << "Case X" << std::endl; break; default: std::cout << "Case Default" << std::endl; break; } return 0; } x_def.h extern const int test_int; x_def.cpp const int test_int = 0; This code will compile correctly on Visual C++ 2008. Furthermore a Montanan friend of mine checked the ISO C++ standard and it appears that any const-integer expression should work. Is this possibly a compiler bug or have I missed something obvious? Here's my compiler version information: Reading specs from C:/MinGW/bin/../lib/gcc/mingw32/3.4.5/specs Configured with: ../gcc-3.4.5-20060117-3/configure --with-gcc --with-gnu-ld --with-gnu-as --host=mingw32 --target=mingw32 --prefix=/mingw --enable-threads --disable-nls --enable-languages=c,c++,f77,ada,objc,java --disable-win32-registry --disable-shared --enable-sjlj-exceptions --enable-libgcj --disable-java-awt --without-x --enable-java-gc=boehm --disable-libgcj-debug --enable-interpreter --enable-hash-synchronization --enable-libstdcxx-debug Thread model: win32 gcc version 3.4.5 (mingw-vista special r3)

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  • Highlighting correctly in an emacs major mode

    - by Paul Nathan
    Hi, I am developing an emacs major mode for a language (aka mydsl). However, using the techniques on xahlee's site doesn't seem to be working for some reason (possibly older emacs dialect..) The key issues I am fighting with are (1) highlighting comments is not working and (2), the use of regexp-opt lines is not working. I've reviewed the GNU manual and looked over cc-mode and elisp mode... those are significantly more complicated than I need. ;;;Standard # to newline comment ;;;Eventually should also have %% to %% multiline block comments (defun mydsl-comment-dwim (arg) "comment or uncomment" (interactive "*P") (require 'newcomment) (let ((deactivate-mark nil) (comment-start "#") (comment-end "") comment-dwim arg))) (defvar mydsl-events '("reservedword1" "reservedword2")) (defvar mydsl-keywords '("other-keyword" "another-keyword")) ;;Highlight various elements (setq mydsl-hilite '( ; stuff between " ("\"\\.\\*\\?" . font-lock-string-face) ; : , ; { } => @ $ = are all special elements (":\\|,\\|;\\|{\\|}\\|=>\\|@\\|$\\|=" . font-lock-keyword-face) ( ,(regexp-opt mydsl-keywords 'words) . font-lock-builtin-face) ( ,(regexp-opt mydsl-events 'words) . font-lock-constant-face) )) (defvar mydsl-tab-width nil "Width of a tab for MYDSL mode") (define-derived-mode mydsl-mode fundamental-mode "MYDSL mode is a major mode for editing MYDSL files" ;Recommended by manual (kill-all-local-variables) (setq mode-name "MYDSL script") (setq font-lock-defaults '((mydsl-hilite))) (if (null mydsl-tab-width) (setq tab-width mydsl-tab-width) (setq tab-width default-tab-width) ) ;Comment definitions (define-key mydsl-mode-map [remap comment-dwim] 'mydsl-comment-dwim) (modify-syntax-entry ?# "< b" mydsl-mode-syntax-table) (modify-syntax-entry ?\n "> b" mydsl-mode-syntax-table) ;;A gnu-correct program will have some sort of hook call here. ) (provide 'mydsl-mode)

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  • rspec and ruby 1.9.1: problem with dummy controller and routes

    - by giorgian
    I want to test a module that basically executes some verify statements, to ensure that actions are invoked with the correct method. # /lib/rest_verification.rb module RestVerification def self.included(base) # :nodoc: base.extend(ClassMethods) end module ClassMethods def verify_rest_actions verify :method => :post, :only => [:create], :redirect_to => { :action => :new } ... end end end I tried this: describe RestVerification do class FooController < ActionController::Base include RestVerification verify_rest_actions def new ; end def index ; end def create ; end def edit ; end def update ; end def destroy ; end end # controller_name 'foo' # this only works with ruby 1.8.7 : 1.9.1 says "uninitialized constant FooController" tests FooController # this works with both before(:each) do ActionController::Routing::Routes.draw do |map| map.resources :foo end end after(:each) do ActionController::Routing::Routes.reload! end it ':create should redirect to :new if invoked with wrong verb' do [:get, :put, :delete].each do |verb| send verb, :create response.should redirect_to(new_foo_url) end end ... end When testing: $ ruby -v ruby 1.8.7 (2010-01-10 patchlevel 249) [i486-linux] $ rake RestVerification :create should redirect to :new if invoked with wrong verb Finished in 0.175586 seconds $ rvm use 1.9.1 Using ruby 1.9.1 p378 $ rake RestVerification :create should redirect to :new if invoked with wrong verb (FAILED - 1) 1) 'RestVerification :create should redirect to :new if invoked with wrong verb' FAILED expected redirect to "http://test.host/foo/new", got redirect to "http://test.host/spec/rails/example/controller_example_group/subclass_1/foo/new" Is this a known issue? Is there a workaround?

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  • Syntactical analysis with Flex/Bison part 2

    - by Imran
    Hallo, I need help in Lex/Yacc Programming. I wrote a compiler for a syntactical analysis for inputs of many statements. Now i have a special problem. In case of an Input the compiler gives the right output, which statement is uses, constant operator or a jmp instructor to which label, now i have to write so, if now a if statement comes, first the first command (before the else) must be give out when the assignment of the if is yes then it must jump to the end because the command after the else isnt needed, so after this jmp then the second command must be give out. I show it in an example maybe you understand what i mean. Input adr. Output if(x==0) 10 if(x==0) Wait 5 20 WAIT 5 else 30 JMP 50 Wait 1 40 WAIT 1 end 50 END like so. I have an idea, maybe i can do it whith a special if statement like IF exp jmp_stmt_end stmt_seq END when the if statement is given in the input the compiler has to recognize the end ofthe statement and like my jmp_stmt in my compiler ( you have to download the files from http://bitbucket.org/matrix/changed-tiny) only to jump to the end. I hope you understand my problem.thanks.

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  • Creating a global variable on the fly. [PHP ENCRYPTION]

    - by stormdrain
    Is there a way to dynamically create constant variables on the fly? The idea is that upon logging into the system, a user would be asked to upload a small text file that would be fread, and assigned to a var that would be accessible throughout the system. If this is possible, just to be clear, would this variable then only be accessible to that user and only while the session is alive? Security being the main concern here, would it be more practical to store the var in a session variable? The plan: Data in the db will be encrypted via mcrypt, and the key will be stored on USB thumbdrives. The user will insert the thumbdrive when going to access the system. Upon logging in, the app will prompt the user to upload the key. They will navigate to the thumbdrive and key. Via fopen and fread, the key will be assigned to a global var which will then allow access to encrypted data, and will be used to encrypt new info being entered to the db. When the user logs out, or session times out, the global var will become empty. Thanks!

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  • How to deal with Unicode strings in C/C++ in a cross-platform friendly way?

    - by Sorin Sbarnea
    On platforms different than Windows you could easily use char * strings and treat them as UTF-8. The problem is that on Windows you are required to accept and send messages using wchar* strings (W). If you'll use the ANSI functions (A) you will not support Unicode. So if you want to write truly portable application you need to compile it as Unicode on Windows. Now, In order to keep the code clean I would like to see what is the recommended way of dealing with strings, a way that minimize ugliness in the code. Type of strings you may need: std::string, std::wstring, std::tstring,char *,wchat_t *, TCHAR*, CString (ATL one). Issues you may encounter: cout/cerr/cin and their Unicode variants wcout,wcerr,wcin all renamed wide string functions and their TCHAR macros - like strcmp, wcscmp and _tcscmp. constant strings inside code, with TCHAR you will have to fill your code with _T() macros. What approach do you see as being best? (examples are welcome) Personally I would go for a std::tstring approach but I would like to see how would do to the conversions where they are necessary.

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  • Rewriting a for loop in pure NumPy to decrease execution time

    - by Statto
    I recently asked about trying to optimise a Python loop for a scientific application, and received an excellent, smart way of recoding it within NumPy which reduced execution time by a factor of around 100 for me! However, calculation of the B value is actually nested within a few other loops, because it is evaluated at a regular grid of positions. Is there a similarly smart NumPy rewrite to shave time off this procedure? I suspect the performance gain for this part would be less marked, and the disadvantages would presumably be that it would not be possible to report back to the user on the progress of the calculation, that the results could not be written to the output file until the end of the calculation, and possibly that doing this in one enormous step would have memory implications? Is it possible to circumvent any of these? import numpy as np import time def reshape_vector(v): b = np.empty((3,1)) for i in range(3): b[i][0] = v[i] return b def unit_vectors(r): return r / np.sqrt((r*r).sum(0)) def calculate_dipole(mu, r_i, mom_i): relative = mu - r_i r_unit = unit_vectors(relative) A = 1e-7 num = A*(3*np.sum(mom_i*r_unit, 0)*r_unit - mom_i) den = np.sqrt(np.sum(relative*relative, 0))**3 B = np.sum(num/den, 1) return B N = 20000 # number of dipoles r_i = np.random.random((3,N)) # positions of dipoles mom_i = np.random.random((3,N)) # moments of dipoles a = np.random.random((3,3)) # three basis vectors for this crystal n = [10,10,10] # points at which to evaluate sum gamma_mu = 135.5 # a constant t_start = time.clock() for i in range(n[0]): r_frac_x = np.float(i)/np.float(n[0]) r_test_x = r_frac_x * a[0] for j in range(n[1]): r_frac_y = np.float(j)/np.float(n[1]) r_test_y = r_frac_y * a[1] for k in range(n[2]): r_frac_z = np.float(k)/np.float(n[2]) r_test = r_test_x +r_test_y + r_frac_z * a[2] r_test_fast = reshape_vector(r_test) B = calculate_dipole(r_test_fast, r_i, mom_i) omega = gamma_mu*np.sqrt(np.dot(B,B)) # write r_test, B and omega to a file frac_done = np.float(i+1)/(n[0]+1) t_elapsed = (time.clock()-t_start) t_remain = (1-frac_done)*t_elapsed/frac_done print frac_done*100,'% done in',t_elapsed/60.,'minutes...approximately',t_remain/60.,'minutes remaining'

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  • Division by zero: Undefined Behavior or Implementation Defined in C and/or C++ ?

    - by SiegeX
    Regarding division by zero, the standards say: C99 6.5.5p5 - The result of the / operator is the quotient from the division of the first operand by the second; the result of the % operator is the remainder. In both operations, if the value of the second operand is zero, the behavior is undefined. C++03 5.6.4 - The binary / operator yields the quotient, and the binary % operator yields the remainder from the division of the first expression by the second. If the second operand of / or % is zero the behavior is undefined. If we were to take the above paragraphs at face value, the answer is clearly Undefined Behavior for both languages. However, if we look further down in the C99 standard we see the following paragraph which appears to be contradictory(1): C99 7.12p4 - The macro INFINITY expands to a constant expression of type float representing positive or unsigned infinity, if available; Do the standards have some sort of golden rule where Undefined Behavior cannot be superseded by a (potentially) contradictory statement? Barring that, I don't think it's unreasonable to conclude that if your implementation defines the INFINITY macro, division by zero is defined to be such. However, if your implementation does not define such a macro, the behavior is Undefined. I'm curious what the consensus on this matter for each of the two languages. Would the answer change if we are talking about integer division int i = 1 / 0 versus floating point division float i = 1.0 / 0.0 ? Note (1) The C++03 standard talks about the library which includes the INFINITY macro.

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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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  • Storing float numbers as strings in android database

    - by sandis
    So I have an app where I put arbitrary strings in a database and later extract them like this: Cursor DBresult = myDatabase.query(false, Constant.DATABASE_NOTES_TABLE_NAME, new String[] {"myStuff"}, where, null, null, null, null, null); DBresult.getString(0); This works fine in all cases except for when the string looks like a float number, for example "221.123123123". After saving it to the database I can extract the database to my computer and look inside it with a DB-viewer, and the saved number is correct. However, when using cursor.getString() the string "221.123" is returned. I cant for the life of me understand how I can prevent this. I guess I could do a cursor.getDouble() on every single string to see if this gives a better result, but that feels sooo ugly and inefficient. Any suggestions? Cheers, edit: I just made a small test program. This program prints "result: 123.123", when I would like it to print "result: 123.123123123" SQLiteDatabase database = openOrCreateDatabase("databas", Context.MODE_PRIVATE, null); database.execSQL("create table if not exists tabell (nyckel string primary key);"); ContentValues value = new ContentValues(); value.put("nyckel", "123.123123123"); database.insert("tabell", null, value); Cursor result = database.query("tabell", new String[]{"nyckel"}, null, null, null, null, null); result.moveToFirst(); Log.d("TAG","result: " + result.getString(0));

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  • Can't combine "LINQ Join" with other tables

    - by FullmetalBoy
    The main problem is that I recieve the following message: "base {System.SystemException} = {"Unable to create a constant value of type 'BokButik1.Models.Book-Author'. Only primitive types ('such as Int32, String, and Guid') are supported in this context."}" based on this LinQ code: IBookRepository myIBookRepository = new BookRepository(); var allBooks = myIBookRepository.HamtaAllaBocker(); IBok_ForfattareRepository myIBok_ForfattareRepository = new Bok_ForfattareRepository(); var Book-Authors = myIBok_ForfattareRepository.HamtaAllaBok_ForfattareNummer(); var q = from booknn in allBooks join Book-Authornn in Book-Authors on booknn.BookID equals Book-Authornn.BookID select new { booknn.title, Book-AuthorID }; How shall I solve this problem to get a class instance that contain with property title and Book-AuthorID? // Fullmetalboy I also have tried making some dummy by using "allbooks" relation with Code Samples from the address http://www.hookedonlinq.com/JoinOperator.ashx. Unfortunately, still same problem. I also have taken account to Int32 due to entity framework http://msdn.microsoft.com/en-us/library/bb896317.aspx. Unfortunatley, still same problem. Using database with 3 tables and one of them is a many to many relationship. This database is used in relation with entity framework Book-Author Book-Author (int) BookID (int) Forfattare (int) Book BookID (int) title (string) etc etc etc

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  • WCF cross-domain policy security error

    - by George2
    Hello everyone, I am using VSTS 2008 + C# + WCF + .Net 3.5 + Silverlight 3.0. I host Silverlight control in an html page and debug it from VSTS 2008 (press F5, then run in VSTS 2008 built-in ASP.Net development web server), then call another WCF service (hosted in another machine running IIS 7.0 + Vista). The WCF service is very simple, just return a constant string to client. When invoking the WCF service from Silverlight, I got the following error message, An error occurred while trying to make a request to URI 'https://LabTest/Test.svc'. This could be due to attempting to access a service in a cross-domain way without a proper cross-domain policy in place, or a policy that is unsuitable for SOAP services. You may need to contact the owner of the service to publish a cross-domain policy file and to ensure it allows SOAP-related HTTP headers to be sent. This error may also be caused by using internal types in the web service proxy without using the InternalsVisibleToAttribute attribute. Please see the inner exception for more details. Here is the clientaccesspolicy.xml file, anything wrong? <?xml version="1.0" encoding="utf-8" ?> <access-policy> <cross-domain-access> <policy> <allow-from http-request-headers="*"> <domain uri="*"> </domain> </allow-from> <grant-to> <resource path="/" include-subpaths="true"></resource> </grant-to> </policy> </cross-domain-access> </access-policy> thanks in advance, George

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  • Trying to calculate large numbers in Python with gmpy. Python keeps crashing?

    - by Ryan Peschel
    I was recommended to use gmpy to assist with calculating large numbers efficiently. Before I was just using python and my script ran for a day or two and then ran out of memory (not sure how that happened because my program's memory usage should basically be constant throughout.. maybe a memory leak?) Anyways, I keep getting this weird error after running my program for a couple seconds: mp_allocate< 545275904->545275904 > Fatal Python error: mp_allocate failure This application has requested the Runtime to terminate it in an unusual way. Please contact the application's support team for more information. Also, python crashes and Windows 7 gives me the generic python.exe has stopped working dialog. This wasn't happening with using standard python integers. Now that I switch to gmpy I am getting this error just seconds in to running my script. I thought gmpy was specialized in dealing with large number arithmetic? For reference, here is a sample program that produces the error: import gmpy2 p = gmpy2.xmpz(3000000000) s = gmpy2.xmpz(2) M = s**p for x in range(p): s = (s * s) % M I have 10 gigs of RAM and without gmpy this script ran for days without running out of memory (still not sure how that happened considering s never really gets larger.. Anyone have any ideas? EDIT: Forgot to mention I am using Python 3.2

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  • How to use boost::transform_iterator to iterate over modifed std::map values?

    - by Frank
    I have an std::map, and I would like to define an iterator that returns modified values. Typically, a std::map<int,double>::iterator iterates over std::pair<int,double>, and I would like the same behavior, just the double value is multiplied by a constant. I tried it with boost::transform_iterator, but it doesn't compile: #include <map> #include <boost/iterator/transform_iterator.hpp> #include <boost/functional.hpp> typedef std::map<int,double> Map; Map m; m[100] = 2.24; typedef boost::binder2nd< std::multiplies<double> > Function; typedef boost::transform_iterator<Function, Map::value_type*> MultiplyIter; MultiplyIter begin = boost::make_transform_iterator(m.begin(), Function(std::multiplies<double>(), 4)); // now want to similarly create an end iterator // and then iterate over the modified map The error is: error: conversion from 'boost ::transform_iterator< boost::binder2nd<multiplies<double> >, gen_map<int, double>::iterator , boost::use_default, boost::use_default >' to non-scalar type 'boost::transform_iterator< boost::binder2nd<multiplies<double> >, pair<const int, double> * , boost::use_default, boost::use_default >' requested What is gen_map and do I really need it? I adapted the transform_iterator tutorial code from here to write this code ...

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  • Flex web application: prevent framerate drop when window is invisible

    - by JayPea
    So there's been a new "feature" in the flash player since version 10.1, which reduces the player's framerate to 2 fps when the application window is out of view. This is good news for performance, but it can break some functionality, such as the Timer class. I have an application which uses a Timer to display a countdown. Given the nature of the application, it is required for the Timer to complete its countdown even if the user is not there to see it. Imagine that you need to give the user only 10 seconds to perform a task. If the user minimizes the window halfway through the counter, they can take as much time as they want and still have 5 seconds left when they return to the window. This apparently can not be avoided with the newer flash players. In Air applications there is the backgroundFrameRate property which can be set to prevent this behavior, but this is part of the WindowedApplication class, so it seems that it is not available in a web application. Does anyone know a way to keep a constant frame rate even when the window is not visible? Thanks

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  • How to calculate the normal of points on a 3D cubic Bézier curve given normals for its start and end points?

    - by Robert
    I'm trying to render a "3D ribbon" using a single 3D cubic Bézier curve to describe it (the width of the ribbon is some constant). The first and last control points have a normal vector associated with them (which are always perpendicular to the tangents at those points, and describe the surface normal of the ribbon at those points), and I'm trying to smoothly interpolate the normal vector over the course of the curve. For example, given a curve which forms the letter 'C', with the first and last control points both having surface normals pointing upwards, the ribbon should start flat, parallel to the ground, slowly turn, and then end flat again, facing the same way as the first control point. To do this "smoothly", it would have to face outwards half-way through the curve. At the moment (for this case), I've only been able to get all the surfaces facing upwards (and not outwards in the middle), which creates an ugly transition in the middle. It's quite hard to explain, I've attached some images below of this example with what it currently looks like (all surfaces facing upwards, sharp flip in the middle) and what it should look like (smooth transition, surfaces slowly rotate round). Silver faces represent the front, black faces the back. Incorrect, what it currently looks like: Correct, what it should look like: All I really need is to be able to calculate this "hybrid normal vector" for any point on the 3D cubic bézier curve, and I can generate the polygons no problem, but I can't work out how to get them to smoothly rotate round as depicted. Completely stuck as to how to proceed!

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  • Implementing list position locator in C++?

    - by jfrazier
    I am writing a basic Graph API in C++ (I know libraries already exist, but I am doing it for the practice/experience). The structure is basically that of an adjacency list representation. So there are Vertex objects and Edge objects, and the Graph class contains: list<Vertex *> vertexList list<Edge *> edgeList Each Edge object has two Vertex* members representing its endpoints, and each Vertex object has a list of Edge* members representing the edges incident to the Vertex. All this is quite standard, but here is my problem. I want to be able to implement deletion of Edges and Vertices in constant time, so for example each Vertex object should have a Locator member that points to the position of its Vertex* in the vertexList. The way I first implemented this was by saving a list::iterator, as follows: vertexList.push_back(v); v->locator = --vertexList.end(); Then if I need to delete this vertex later, then rather than searching the whole vertexList for its pointer, I can call: vertexList.erase(v->locator); This works fine at first, but it seems that if enough changes (deletions) are made to the list, the iterators will become out-of-date and I get all sorts of iterator errors at runtime. This seems strange for a linked list, because it doesn't seem like you should ever need to re-allocate the remaining members of the list after deletions, but maybe the STL does this to optimize by keeping memory somewhat contiguous? In any case, I would appreciate it if anyone has any insight as to why this happens. Is there a standard way in C++ to implement a locator that will keep track of an element's position in a list without becoming obsolete? Much thanks, Jeff

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  • How to use data receive event in Socket class?

    - by affan
    I have wrote a simple client that use TcpClient in dotnet to communicate. In order to wait for data messages from server i use a Read() thread that use blocking Read() call on socket. When i receive something i have to generate various events. These event occur in the worker thread and thus you cannot update a UI from it directly. Invoke() can be use but for end developer its difficult as my SDK would be use by users who may not use UI at all or use Presentation Framework. Presentation framework have different way of handling this. Invoke() on our test app as Microstation Addin take a lot of time at the moment. Microstation is single threaded application and call invoke on its thread is not good as it is always busy doing drawing and other stuff message take too long to process. I want my events to generate in same thread as UI so user donot have to go through the Dispatcher or Invoke. Now i want to know how can i be notified by socket when data arrive? Is there a build in callback for that. I like winsock style receive event without use of separate read thread. I also do not want to use window timer to for polling for data. I found IOControlCode.AsyncIO flag in IOControl() function which help says Enable notification for when data is waiting to be received. This value is equal to the Winsock 2 FIOASYNC constant. I could not found any example on how to use it to get notification. If i am write in MFC/Winsock we have to create a window of size(0,0) which was just used for listening for the data receive event or other socket events. But i don't know how to do that in dotnet application.

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  • Treating differential operator as algebraic entity

    - by chappar
    I know that this question is offtopic and don't belong here. But i didn't know somewhere else to ask. So here is the question. I was reading e:the story of a number by Eli Maor, where he treats differential operator as just like any algebraic entity. For example if we have a differential equation like y’’ + 5y’ - 6y = 0. This can be treaed as (D^2 + 5D – 6)y = 0. So, either y = 0 (trivial solution) or (D^2 + 5D – 6) = 0. Factoring out above equation we get (D-1)(D+6)= 0 with solutions as D = 1 and D = -6. Since D does not have any meaning on its own, multiplying by y on both the sides we get Dy = y and Dy = -6y for which the solutions are Ae^x and Be^-6x. Combining these 2 solutions we get Ae^x + Be^-6x. Now my doubt is this approach break when we have an equation like D^2y = 0. Which means y = 0 (again trivial) or D^2 = 0 which means D = 0. Now Dy = y*0 = 0. That means y = C ( a constant). The actual answer should be Cx. I know that it is stupidity to treat D^2 = 0 as D = 0, it led me to doubt the entire process of treating differential equation as algebraic equation. Can someone throw light on this? Or any other site where i might get answer?

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  • Error while compiling pjsip 2 for cxode 4.3.2 and SDK 5.1

    - by Linus Persson
    I'm trying to compile pjsip version 2 using the terminal and I'm getting constant error no matter what I try. Been looking for the answer all over the internet including stackoverflow. I downloaded pjsip version 2 using their subversion repository today so all files should be up to date. When following this guide: http://trac.pjsip.org/repos/wiki/Getting-Started/iPhone I get this error after running "make dep && make clean && make": ld: symbol(s) not found for architecture armv7 collect2: ld returned 1 exit status make[2]: *** [../bin/pjsua-arm-apple-darwin9] Error 1 make[1]: *** [pjsua] Error 2 make: *** [all] Error 1 When using the above guide combined with this guide: http://lists.pjsip.org/pipermail/pjsip_lists.pjsip.org/2011-October/013481.html I get this error after running "make dep && make clean && make": ld: symbol(s) not found for architecture arm collect2: ld returned 1 exit status make[2]: *** [../bin/pjsua-arm-apple-darwin10] Error 1 make[1]: *** [pjsua] Error 2 make: *** [all] Error 1 I've included /pjlib/include/pj/config_site.h with the following code: #define PJ_CONFIG_IPHONE 1 #include <pj/config_site_sample.h> How do I get pjsip to compile without errors? Please consider that I'm new to this, thank you!

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  • one two-directed tcp socket OR two one-directed? (linux, high volume, low latency)

    - by osgx
    Hello I need to send (interchange) a high volume of data periodically with the lowest possible latency between 2 machines. The network is rather fast (e.g. 1Gbit or even 2G+). Os is linux. Is it be faster with using 1 tcp socket (for send and recv) or with using 2 uni-directed tcp sockets? The test for this task is very like NetPIPE network benchmark - measure latency and bandwidth for sizes from 2^1 up to 2^13 bytes, each size sent and received 3 times at least (in teal task the number of sends is greater. both processes will be sending and receiving, like ping-pong maybe). The benefit of 2 uni-directed connections come from linux: http://lxr.linux.no/linux+v2.6.18/net/ipv4/tcp_input.c#L3847 3847/* 3848 * TCP receive function for the ESTABLISHED state. 3849 * 3850 * It is split into a fast path and a slow path. The fast path is 3851 * disabled when: ... 3859 * - Data is sent in both directions. Fast path only supports pure senders 3860 * or pure receivers (this means either the sequence number or the ack 3861 * value must stay constant) ... 3863 * 3864 * When these conditions are not satisfied it drops into a standard 3865 * receive procedure patterned after RFC793 to handle all cases. 3866 * The first three cases are guaranteed by proper pred_flags setting, 3867 * the rest is checked inline. Fast processing is turned on in 3868 * tcp_data_queue when everything is OK. All other conditions for disabling fast path is false. And only not-unidirected socket stops kernel from fastpath in receive

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  • Program structure in long running data processing python script

    - by fmark
    For my current job I am writing some long-running (think hours to days) scripts that do CPU intensive data-processing. The program flow is very simple - it proceeds into the main loop, completes the main loop, saves output and terminates: The basic structure of my programs tends to be like so: <import statements> <constant declarations> <misc function declarations> def main(): for blah in blahs(): <lots of local variables> <lots of tightly coupled computation> for something in somethings(): <lots more local variables> <lots more computation> <etc., etc.> <save results> if __name__ == "__main__": main() This gets unmanageable quickly, so I want to refactor it into something more manageable. I want to make this more maintainable, without sacrificing execution speed. Each chuck of code relies on a large number of variables however, so refactoring parts of the computation out to functions would make parameters list grow out of hand very quickly. Should I put this sort of code into a python class, and change the local variables into class variables? It doesn't make a great deal of sense tp me conceptually to turn the program into a class, as the class would never be reused, and only one instance would ever be created per instance. What is the best practice structure for this kind of program? I am using python but the question is relatively language-agnostic, assuming a modern object-oriented language features.

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