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• Style question: Writing "this." before instance variable and methods: good or bad idea?

  - by Uri

  One of my nasty (?) programming habits in C++ and Java is to always precede calls or accesses to members with a this. For example: this.process(this.event). A few of my students commented on this, and I'm wondering if I am teaching bad habits. My rationale is: 1) Makes code more readable — Easier to distinguish fields from local variables. 2) Makes it easier to distinguish standard calls from static calls (especially in Java) 3) Makes me remember that this call (unless the target is final) could end up on a different target, for example in an overriding version in a subclass. Obviously, this has zero impact on the compiled program, it's just readability. So am I making it more or less readable? Related Question Note: I turned it into a CW since there really isn't a correct answer.

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• Any good way to set the exit status of a Cocoa application?

  - by buglesareking

  I have a Cocoa app which interacts with a server and displays a GUI. If there is a fatal error, I display an alert and exit. I'd like to set the exit status to a non-zero value to reflect that an error occurred, for ease of interaction with some other UNIX based tools. Unfortunately I've been unable to find a good way to do so - NSApplication doesn't seem to have any way to set an exit status. At the moment, I've subclassed NSApplication and added an exitStatus ivar (which I set in my app delegate when necessary), then overridden -terminate: so that it calls exit(exitStatus). This works fine, but it seems a bit grungy to me, not to mention that I may be missing something important that the stadnard `terminate: is doing behind the scenes. I can't call [super terminate:sender] in my subclassed method, because that exit()s without giving me a chance to set the status. Am I missing something obvious?

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• What's a good way to detect wrap-around in a fixed-width message counter?

  - by Kristo

  I'm writing a client application to communicate with a server program via UDP. The client periodically makes requests for data and needs to use the most recent server response. The request message has a 16-bit unsigned counter field that is echoed by the server so I can pair requests with server responses. Since it's UDP, I have to handle the case where server responses arrive out of order (or don't arrive at all). Naively, that means holding on to the highest message counter seen so far and dropping any incoming message with a lower number. But that will fail as soon as we pass 65535 messages and the counter wraps back to zero. Is there a good way to detect (with reasonable probability) that, for example, message 5 actually comes after message 65,000? The implementation language is C++.

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• Explicit initialization of struct/class members

  - by Zephon

  struct some_struct{ int a; }; some_struct n = {}; n.a will be 0 after this; I know this braces form of initialization is inherited from C and is supported for compatibility with C programs, but this only compiles with C++, not with the C compiler. I'm using Visual C++ 2005. In C this type of initialization struct some_struct n = {0}; is correct and will zero-initialize all members of a structure. Is the empty pair of braces form of initialization standard? I first saw this form of initialization in a WinAPI tutorial from msdn.

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• Windows media player control with .NET

  - by brovar

  What I want to do is to read media files (pics and videos) from a directory and display them one by one using the WMP control (AxWMPLib.AxWindowsMediaPlayer). In its older version it was enough to check the file's duration to distinguish images from videos, the new one randomly shows movies' duration properly or as zero. Does anyone know any other way of finding out what file is being proceeded withouth checking its extension (as a file can have an extension of .abc or so)? I'll be very grateful for any help. (Sorry for my lousy English.)

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• What happens to class members when malloc is used instead of new?

  - by Felix

  I'm studying for a final exam and I stumbled upon a curious question that was part of the exam our teacher gave last year to some poor souls. The question goes something like this: Is the following program correct, or not? If it is, write down what the program outputs. If it's not, write down why. The program: #include<iostream.h> class cls { int x; public: cls() { x=23; } int get_x(){ return x; } }; int main() { cls *p1, *p2; p1=new cls; p2=(cls*)malloc(sizeof(cls)); int x=p1->get_x()+p2->get_x(); cout<<x; return 0; } My first instinct was to answer with "the program is not correct, as new should be used instead of malloc". However, after compiling the program and seeing it output 23 I realize that that answer might not be correct. The problem is that I was expecting p2->get_x() to return some arbitrary number (whatever happened to be in that spot of the memory when malloc was called). However, it returned 0. I'm not sure whether this is a coincidence or if class members are initialized with 0 when it is malloc-ed. Is this behavior (p2->x being 0 after malloc) the default? Should I have expected this? What would your answer to my teacher's question be? (besides forgetting to #include <stdlib.h> for malloc :P)

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• Initializing structs in C++

  - by Neil Butterworth

  As an addendum to this question, what is going on here: #include <string> using namespace std; struct A { string s; }; int main() { A a = {0}; } Obviously, you can't set a std::string to zero. Can someone provide an explanation (backed with references to the C++ Standard, please) about what is actually supposed to happen here? And then explain for example): int main() { A a = {42}; } Are either of these well-defined? Once again an embarrassing question for me - I always give my structs constructors, so the issue has never arisen before.

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• insane transformations of a view

  - by Mike

  I have this view and I do some rotation transformation to it using something like myView.transform = CGAffineTransformMakeRotation(degreesToRadian(90)); //The view was originally at angle 0. at some other point of my code, I would like to scale the view animating it, so I do [UIView beginAnimations:nil context:NULL]; [UIView setAnimationDuration:1.0]; myViews.transform = CGAffineTransformMakeScale(2.0f, 2.0f); [UIView commitAnimations]; but when I do that the animation is performed as the view is at 0 degrees, ignoring the previous transformation. It simply assumes as the view is yet at zero degrees, so, this animation scales the view and rotates it back to 0 degrees (!!!!?????) Is this some bug or am I missing something? thanks.

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• Zend Framework: The form filter I am using is not filtering!

  - by Andrew

  So I have a form that is using the Zend_Filter_Null filter. When I call it directly, it works: $makeZeroNull = new Zend_Filter_Null(); $null = $makeZeroNull->filter('0'); //$null === null However, when I try to add it to an element in my form, it doesn't filter the value when I call getValue(). class My_Form extends Zend_Form { public function init() { $makeZeroNull = new Zend_Filter_Null(); $this->addElement('text', 'State_ID', array('filters' => array($makeZeroNull))); } } //in controller if ($form->isValid($_POST)) { $zero = $form->State_ID->getValue(); //getValue() should return null, but it is returning 0 } What is going on? What am I doing wrong?

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• Eliminating cyclic flows from a graph

  - by Jon Harrop

  I have a directed graph with flow volumes along edges and I would like to simplify it by removing all cyclic flows. This can be done by finding the minimum of the flow volumes along each edge in any given cycle and reducing the flows of every edge in the cycle by that minimum volume, deleting edges with zero flow. When all cyclic flows have been removed the graph will be acyclic. For example, if I have a graph with vertices A, B and C with flows of 1 from A?B, 2 from B?C and 3 from C?A then I can rewrite this with no flow from A?B, 1 from B?C and 2 from C?A. The number of edges in the graph has reduced from 3 to 2 and the resulting graph is acyclic. Which algorithm(s), if any, solve this problem?

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• MySQL load data null values

  - by SP1

  Hello, I have a file that can contain from 3 to 4 columns of numerical values which are separated by comma. Empty fields are defined with the exception when they are at the end of the row: 1,2,3,4,5 1,2,3,,5 1,2,3 The following table was created in MySQL: +-------+--------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+--------+------+-----+---------+-------+ | one | int(1) | YES | | NULL | | | two | int(1) | YES | | NULL | | | three | int(1) | YES | | NULL | | | four | int(1) | YES | | NULL | | | five | int(1) | YES | | NULL | | +-------+--------+------+-----+---------+-------+ I am trying to load the data using MySQL LOAD command: load data infile '/tmp/testdata.txt' into table moo fields terminated by "," lines terminated by "\n"; The resulting table: +------+------+-------+------+------+ | one | two | three | four | five | +------+------+-------+------+------+ | 1 | 2 | 3 | 4 | 5 | | 1 | 2 | 3 | 0 | 0 | | 1 | 2 | 3 | NULL | NULL | +------+------+-------+------+------+ The problem lies with the fact that when a field is empty in the raw data and is not defined, MySQL for some reason does not use the columns default value (which is NULL) and uses zero. NULL is used correctly when the field is missing alltogether. Unfortunately, I have to be able to distinguish between NULL and 0 at this stage so any help would be appreciated. Thanks S.

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• Why does GetTextFace always return "system"?

  - by user545142

  I am trying to get the font of controls in other applications. When I try WM_GETFONT, it returns 0. This my code: [DllImport("User32.DLL")] public static extern IntPtr SendMessage(IntPtr hWnd, int Msg, int wParam, int lParam); IntPtr fx = SendMessage(button1.Handle, 0x31, 0, 0); When I use GetTextFace with a button, it always returns "system". This is my code: StringBuilder Buff = new StringBuilder(256); IntPtr dc = GetDCEx(button1.Handle, IntPtr.Zero, DeviceContextValues.Window |DeviceContextValues.Cache | DeviceContextValues.ClipSiblings | DeviceContextValues.IntersectRgn); IntPtr hfont = GetTextFace(dc, 256, Buff); Of course I'm sure I changed the font type. How can I solve this problem? I am using C# under Windows 7.

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• Ambiguous Evaluation of Lambda Expression on Array

  - by Joe

  I would like to use a lambda that adds one to x if x is equal to zero. I have tried the following expressions: t = map(lambda x: x+1 if x==0 else x, numpy.array) t = map(lambda x: x==0 and x+1 or x, numpy.array) t = numpy.apply_along_axis(lambda x: x+1 if x==0 else x, 0, numpy.array) Each of these expressions returns the following error: ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all() My understanding of map() and numpy.apply_along_axis() was that it would take some function and apply it to each value of an array. From the error it seems that the the lambda is being evaluated as x=array, not some value in array. What am I doing wrong? I know that I could write a function to accomplish this but I want to become more familiar with the functional programming aspects of python.

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• How to get min/max of two integers in Postgres/SQL?

  - by HRJ

  How do I find the maximum (or minimum) of two integers in Postgres/SQL? One of the integers is not a column value. I will give an example scenario: I would like to subtract an integer from a column (in all rows), but the result should not be less than zero. So, to begin with, I have: UPDATE my_table SET my_column = my_column - 10; But this can make some of the values negative. What I would like (in pseudo code) is: UPDATE my_table SET my_column = MAXIMUM(my_column - 10, 0);

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• The shortest way to convert infix expressions to postfix (RPN) in C

  - by kuszi

  Original formulation is given here (you can try also your program for correctness) . Additional rules: 1. The program should read from standard input and write do standard output. 2. The program should return zero to the calling system/program. 3. The program should compile and run with gcc -O2 -lm -s -fomit-frame-pointer. The challenge has some history: the call for short implementations has been announced at the Polish programming contest blog in September 2009. After the contest, the shortest code was 81 chars long. Later on the second call has been made for even shorter code and after the year matix2267 published his solution in 78 bytes: main(c){read(0,&c,1)?c-41&&main(c-40&&(c%96<27||main(c),putchar(c))):exit(0);} Anyone to make it even shorter or prove this is impossible?

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• Need to read .symtab

  - by user361190

  I am frustrated. I have a simple doubt .. I compile a simple program with gcc and if I see the section header using objdump, it does not show the section ".symtab". for the same a.out file, readelf shows the section. see the below snip - [25] .symtab SYMTAB 00000000 000ca4 000480 10 26 2c 4 [26] .strtab STRTAB 00000000 001124 00025c 00 0 0 1 Why ? In the default linker script I don't find a definition for .symtab section. If I add a definition by myself like in the linker script : .... PROVIDE(__start_sym) .symtab : { *(.symtab)} PROVIDE(__end_sym) .... the difference b/w the addresses of __start_sym and __end_sym is zero, which means no such section is added in the output file. But the readelf is able to read the section and dump the contents of this section .. How ? why ?

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• How to do Linq aggregates when there might be an empty set?

  - by Shaul

  I have a Linq collection of Things, where Thing has an Amount (decimal) property. I'm trying to do an aggregate on this for a certain subset of Things: var total = myThings.Sum(t => t.Amount); and that works nicely. But then I added a condition that left me with no Things in the result: var total = myThings.Where(t => t.OtherProperty == 123).Sum(t => t.Amount); And instead of getting total = 0 or null, I get an error: System.InvalidOperationException: The null value cannot be assigned to a member with type System.Decimal which is a non-nullable value type. That is really nasty, because I didn't expect that behavior. I would have expected total to be zero, maybe null - but certainly not to throw an exception! What am I doing wrong? What's the workaround/fix?

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• Anyone Know a Great Sparse One Dimensional Array Library in Python?

  - by TheJacobTaylor

  I am working on an algorithm in Python that uses arrays heavily. The arrays are typically sparse and are read from and written to constantly. I am currently using relatively large native arrays and the performance is good but the memory usage is high (as expected). I would like to be able to have the array implementation not waste space for values that are not used and allow an index offset other than zero. As an example, if my numbers start at 1,000,000 I would like to be able to index my array starting at 1,000,000 and not be required to waste memory with a million unused values. Array reads and writes needs to be fast. Expanding into new territory can be a small delay but reads and writes should be O(1) if possible. Does anybody know of a library that can do it? Thanks!

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• Why does C++ linking use virtually no CPU?

  - by John

  On a native C++ project, linking right now can take a minute or two, yet during this time CPU drops from 100% during compilation to virtually zero. Does this mean linking is primarily a disk activity? If so, is this the main area an SSD would make big changes? But, why aren't all my OBJ files (or as many as possible) kept in RAM after compilation to avoid this? With 4Gb of RAM I should be able to save a lot of disk access and make it CPU-bound again, no?

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• SQL Azure server as unit of billing

  - by vtortola

  Hi, One of the azure training kit presentation says: Each account has zero or more logical servers Provisioned via a common portal Establishes a billing instrument Each logical server has one or more databases Contains metadata about database & usage Unit of authentication, geo-location, billing, reporting Generated DNS-based name Each database has standard SQL objects Users, Tables, Views, Indices, etc Unit of consistency So now I'm lost :D. Were not the databases themselves the units of billing? I mean, I thought that servers were just like logical containers and you were charged per number and size of databases. How servers are billed? Thanks.

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• Incrmenting a Cookies with PHP (Beginner Question)

  - by BandonRandon

  Hello, I have used sessions before but never cookies. I would like to use cookies for two reasons: 1) it's something new to learn 2) I would like to have the cookie expire in an hour or so (i know in the code example it expires in 40 sec) I am trying to write a basic if statement that if($counter=="1") { //do this second } elseif ($counter >="2") { //do this every time after the first and second } else {// this is the first action as counter is zero } Here is the code I'm using to set the cookie: // if cookie doesnt exsist, set the default if(!isset($_COOKIE["counter_cookie"])) { $counter = setcookie("counter_cookie", 0 ,time()+40); } // increment it $counter++; // save it setcookie("counter_cookie", $counter,time()+40); $counter = $_COOKIE["counter_cookie"]; The problem is that the counter will be set from 0 to 1 but won't be set from 1 to 2 and so on. Any help would be great I know this is a really simple stupid question :| Thanks!

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• When using the Facebook Connect Actionscript API (no JS, just straight Flash), how can I listen for

  - by techno

  Hey guys, When using the Facebook Connect AS API, the user will be prompted to log in to FB in a pop up window. At this point I want to block interaction in my flash movie and wait for them to complete logging in (or potentially close/cancel and not log in). I have seen examples where people put up a Flex "Alert" box with some hint like "Press ok once you have logged into facebook", but I want to automatically listen for them logging in or canceling/closing the popup window without logging in. Is there an event I can listen for with flash? So far I am using ZERO javascript, but I guess I could add a little if it is needed for this... I definitely want to avoid having some sort of "Press OK" alert box, but instead have the flash application automatically react to the user logging in with the popup window.

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• Haskell: writing the result of a computation to file

  - by peterwkc

  I have a function which creates a tuple after computation, but I would like to write it to file. I know how to write to a file using writeFile, but do not know how to combine the computation and monads IO together in the type signature. This is my code. invest :: ([Char]->Int->Int->([Char], Int) ) -> [Char]->Int->Int->([Char], Int) invest myinvest x y = myinvest x y myinvest :: [Char]->Int->Int->([Char], Int) myinvest w x y | y > 0 = (w, x + y) | otherwise = error "Invest amount must greater than zero" where I have a function which computes the maximum value from a list, but I want this function to receive input from a file, and then perform the computation of maximum value. maximuminvest :: (Ord a) => [a] -> a maximuminvest [] = error "Empty Invest Amount List" maximuminvest [x] = x maximuminvest (x:xs) | x > maxTail = x | otherwise = maxTail where maxTail = maximuminvest xs Please help. Thanks.

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• Hebbian learning

  - by Bane

  I have asked another question on Hebbian learning before, and I guess I got a good answer which I accepted, but, the problem is that I now realize that I've mistaken about Hebbian learning completely, and that I'm a bit confused. So, could you please explain how it can be useful, and what for? Because the way Wikipedia and some other pages describe it - it doesn't make sense! Why would we want to keep increasing the weight between the input and the output neuron if the fire together? What kind of problems can it be used to solve, because when I simulate it in my head, it certainly can't do the basic AND, OR, and other operations (say you initialize the weights at zero, the output neurons never fire, and the weights are never increased!)

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• Corporate Environment [closed]

  - by aloneguid

  How do you guys live in corporate environment? Especially talk to each other (developer to developer). I find it extremely hard as any question goes to "please book a meeting for that". Sometimes I get a chance to ask sb sth on the kitchen but that's it. Booked meetings are just stupidest thing ever, 'cos people talk about nothing specific and you have to wait days for them to happen. Weekly "scrums" are even more stupid as they usually take about 10 mins and you could do the same in 1 minute by email, no useful info or communication et all. All that leads to zero understanding of the product, no connection to customers, development in own isolated cubible, throwing out most of your code because that's not what was needed and you never know what the product is really aimed to do. Sad :(

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