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• When are C++ macros beneficial?

  - by Motti

  The C preprocessor is justifiably feared and shunned by the C++ community. In-lined functions, consts and templates are usually a safer and superior alternative to a #define. The following macro: #define SUCCEEDED(hr) ((HRESULT)(hr) >= 0) is in no way superior to the type safe: inline bool succeeded(int hr) { return hr >= 0; } But macros do have their place, please list the uses you find for macros that you can't do without the preprocessor. Please put each use-cases in a seperate answer so it can be voted up and if you know of how to achieve one of the answers without the preprosessor point out how in that answer's comments.

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• Function calls in virtual machine killing performance

  - by GenTiradentes

  I wrote a virtual machine in C, which has a call table populated by pointers to functions that provide the functionality of the VM's opcodes. When the virtual machine is run, it first interprets a program, creating an array of indexes corresponding to the appropriate function in the call table for the opcode provided. It then loops through the array, calling each function until it reaches the end. Each instruction is extremely small, typically one line. Perfect for inlining. The problem is that the compiler doesn't know when any of the virtual machine's instructions are going to be called, as it's decided at runtime, so it can't inline them. The overhead of function calls and argument passing is killing the performance of my VM. Any ideas on how to get around this?

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• Unsigneds in order to prevent negative numbers

  - by Bruno Brant

  let's rope I can make this non-sujective Here's the thing: Sometimes, on fixed-typed languages, I restrict input on methods and functions to positive numbers by using the unsigned types, like unsigned int or unsigned double, etc. Most libraries, however, doesn't seem to think that way. Take C# string.Length. It's a integer, even though it can never be negative. Same goes for C/C++: sqrt input is an int or a double. I know there are reasons for this ... for example your argument might be read from a file and (no idea why) you may prefer to send the value directly to the function and check for errors latter (or use a try-catch block). So, I'm assuming that libraries are way better designed than my own code. So what are the reasons against using unsigned numbers to represent positive numbers? It's because of overflow when we cast then back to signed types?

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• A good way to implement useable Callbacks in C++

  - by Marcel J.

  I have a custom Menu class written in C++. To seperate the code into easy-to-read functions I am using Callbacks. Since I don't want to use Singletons for the Host of the Menu I provide another parameter (target) which will be given to the callback as the first parameter (some kind of workaround for the missing "this" reference). Registration-Signature AddItem(string s, void(*callback)(void*,MenuItem*), void* target = NULL) Example of a Registration menu->AddItem(TRANSLATE, "translate", &MyApp::OnModeSelected); Example of a Handler /* static */ void MyApp::OnModeSelected(void* that, MenuItem* item) { MyApp *self = (MyApp*)that; self->activeMode = item->text; } Is there anything one could consider dirty with this approach? Are there maybe better ones?

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• Are there any context-sensitive code search tools?

  - by Vicky

  I have been getting very frustrated recently in dealing with a massive bulk of legacy code which I am trying to get familiar with. Say I try to search for a particular function call, I get loads of results that turn out to be completely irrelevant; some of them are easy to spot, eg a comment saying // Fixed functionality in foo() so don't need to handle this here any more But others are much harder to spot manually, because they turn out to be calls from other functions in modules that are only compiled in certain cases, or are part of a much larger block of code that is #if 0'd out in its entirety. What I'd like would be a search tool that would allow me to search for a term and give me the choice to include or exclude commented out or #if 0'd out code. Then the search results would be displayed alongside a list of #defines that are required in order for that snippet of code to be relevant. I'm working in C / C++, but other than the specific comment syntax I guess the techniques should be more generally applicable. Does such a tool exist?

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• How to inline string.h function on linux?

  - by tz1

  I want to optimize some code such that all the functions in string.h will be inlined. I'm on x86_64. I've tried -O3, -minline-all-stringops and when I do "nm a.out" it shows it is calling the glibc version. Checking with gcc -S, I see the calls. What am I missing? There are dozens of #ifdef _SOME_SETTING_ in string.h, and bits/string3.h shows the inline version, but I don't know how to get there. for example: $ cat test.c include main() { char *a, b; strcpy(b,a); } / When compiled with: gcc -minline-all-stringops -O6 -I. -S -o test.S test.c .file "test.c" .text .p2align 4,,15 .globl main .type main, @function main: .LFB12: .cfi_startproc subq $8, %rsp .cfi_def_cfa_offset 16 xorl %esi, %esi xorl %edi, %edi call strcpy addq $8, %rsp .cfi_def_cfa_offset 8 ret .cfi_endproc .LFE12: .size main, .-main .ident "GCC: (GNU) 4.5.1 20100924 (Red Hat 4.5.1-4)" .section .note.GNU-stack,"",@progbits */

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• How can I (from a script) add something to the zsh command history?

  - by Brandon

  I'd like to be able to look through my command history and know the context from which I issued various commands--in other words, "what directory was I in?" There are various ways I could achieve this, but all of them (that I can think of) would require manipulating the zsh history to add (for instance) a commented line with the result of $(pwd). (I could create functions named cd & pushd & popd etc, or I could use zsh's preexec() function and maybe its periodic() function to add the comment line at most every X seconds, just before I issue a command, or perhaps there's some other way.) The problem is, I don't want to directly manipulate the history file and bypass the shell's history mechanism, but I can't figure out a way (with the fc command, for instance) to add something to the history without actually typing it on the command line. How could I do this?

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• GNUPlot: plot different ranges with different styles

  - by Mr. Shickadance

  Hello all, I know this should be pretty simple, but I haven't been able to find a similar example. I need to plot different ranges of a datafile differently, but on the same graph. For instance, say my datafile represents a function with x and y values. I want to plot the first N values using a style like lines, and then the next M values using a different style, like points. I was thinking I would need a plot command similar to this: plot [1:5] "my.data" using 1:2 with lines, [6:12] using 1:2 with points, [13:19] using 1:2 with lines Essentially I want to distinguish different areas of the functions. Any ideas? I am sorry if it sounds like I'm rambling but I am quite stumped. Thanks in advance!

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• Enter purchase order received quantity by code

  - by user733916

  In purchase order form - Line - Tab Quantity, there is Received, Delivery Reminder and Ordered. I want to be able to entry those field by X++ code, because currently our company still entry data into old system. I can retrieve the arrival purchase order goods data from that old system, then I want to entry those retrieved data by code into Axapta. What table and field should I consider when doing that? What functions available to easily update each PO lines received quantity? Sample Code is nice.

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• namespacing large javascript like jquery

  - by frenchie

  I have a very large javascript file: it's over 9,000 lines. The code looks like this: var GlobalVar1 = ""; var GlobalVar2 = null; function A() {...} function B(SomeParameter) {...} I'm using the google compiler and the global variables and functions get renamed a,b,c... and there's a good change that there might be some collision later with some outside code. What I want to do is have my code organized like the jquery library where everything is accessible with $. Is there a way to namespace my code so that everything is behind a # character for example. I'd like to have this to call my code: #.GlobalVar #.functionA(SomeParameter) How can I do this? Thanks.

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• What is the use of reflection in Java/C# etc

  - by zengr

  I was just curious, why should we use reflection in the first place? // Without reflection Foo foo = new Foo(); foo.hello(); // With reflection Class cls = Class.forName("Foo"); Object foo = cls.newInstance(); Method method = cls.getMethod("hello", null); method.invoke(foo, null); We can simply create an object and call the class's method, but why do the same using forName, newInstance and getMthod functions? To make everything dynamic?

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• Switching function states

  - by webzide

  Dear experts, I would like to implement a API of Javascript that sort of resemble a light switch. For instance, there are two buttons on the actual HTML page act as the UI. Both of the buttons have event handlers that invokes a different function. Each function have codes that act like a state, for instance. button1.onclick=function (){ $("div").click( //code effects 2 ) } button2.onclick=function (){ $("div").click( //Code effects 2 ) } I the code works fine on the surface but the 2 state functions overlap. the effects is going to take place for the rest of the way until the next reload of the document. Basically what I want to achieve is that when 1 button is clicked, it will switch "OFF" the state of function invoked by the other button and vice versa. Thus, the effects achieved are unique are not overlapped. Is there anyway to achieve this or could any experts point me to the right direction. Thanks in advance.

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• Whats the API Key for in Google Maps API V3?

  - by Brandon

  In the older version of the API, I'd have to insert the javascript into the page using something like this for just basic functionality to work: http://maps.google.com/maps?file=api&v=2&key=GoogleMapsAPIKey Where I had to configure the API key for each individual site. Looking at the documentation, it says to get a basic map working I just need this: http://maps.google.com/maps/api/js?sensor=true/false Where does the API key fit in? Do I need to worry about it if I just plan on using a basic map and marker and none of the more advanced functions?

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• Wait for function to finish before executing the rest

  - by Wurlitzer

  When the user refreshes the page, defaultView() is called, which loads some UI elements. $.address.change() should execute when defaultView() has finished, but this doesn't happen all the time. $.address.change() cannot be in the success: callback, as it's used by the application to track URL changes. defaultView(); function defaultView() { $('#tout').fadeOut('normal', function() { $.ajax({ url: "functions.php", type: "GET", data: "defaultview=true", async: false, success: function (response) { $('#tout').html(response).fadeIn('normal'); } }); }); } $.address.change(function(hash) { hash = hash.value; getPage(hash); }); I'm at a loss as to how to make $.address.change() wait for defaultView() to finish. Any help would be appreciated.

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• Can this be done with multiple inhertance?

  - by Milo

  Here is what I would like to do. Say I have Class Widget. I then create Button from Widget. I then create ModifiedWidget which re-implements certain functions of Widget. I then want Button to use ModifiedWidget rather than plain Widget. Is this possible to do some how? Thanks class Button : public Widget; class SuperButton : public Button, public ModifiedWidget; I'm just not sure if that would do what I want it to though.

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• how to call a javascript function in the top frame?

  - by Rory

  This seems really simple, but how do I call a javascript function that's defined in the top-level html, from a child frame? top html doc - 1st level frame - 2nd level frame my top html doc has a function called testFn(). In the 2nd level frame I have a button with onclick="top.testFn();" but this doesn't call the testFn(). In Firebug if I use a watch to execute top.testFn(); it says TypeError: testFn() is not a function. Should this all just work - in which case it's a problem with my documents, or is there some other way to call functions in the top-level window?

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• sigprocmask not working

  - by EpsilonVector

  I'm using sigprocmask as follows: void mask(){ sigset_t new_set,old_set; sigemptyset(&new_set); sigaddset(&new_set,SIGALRM); sigprocmask(SIG_BLOCK, &new_set, &old_set); } and to my surprise a function which prints a big list somehow gets interrupted by the signal, even though I invoke mask() at its beginning. It looks as if mask fails, since my function doesn't invoke any other functions and therefore nowhere in its run should an unmask() happen. What can cause sigprocmask to fail?

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• Reordering Lists like playlists in the media player

  - by CrazyBS

  Hi, I have a list of items that are displayed using a ListView from a SQLCursor. The SQL table includes(as well as other things) a _id field and an order field. I use the order field to sort the list before it gets to the ListView. What I need is a widget like the MediaPlayer has in its playlist view. It allows you to click the icon and drag the item in the playlist around and put it into a new order. With that ability I can then retrieve the new order and update the SQL table with the new order. However, I am not having any luck finding any clues to help me add that functionality into my program. The question is whether I can use existing functions to help me, or do I need to manually program motion events and such until I get nearly the same functionality.

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• Correct handling of return data

  - by Serhiy

  Hello, I have a question related to correct handling of returns of the DAO library I'm writing for one project. This library probably is going to be used by another people and I want to do it correctly. So I would like to know, how I should deal with return statements of the functions of my DAO. Example 1 I have function to getCustomer which should return String. In case query doesn't return any result should I return null, empty string or throw some kind of Exception? Example 2 I have function getCutomerList which return ArrayList. In case query doesn't return any result should I return null, empty ArrayList or throw some Exception? Example 3 Some sql exception was detected, what should I do: throw exception or do try..catch of the block where it can occur? What is the "good" practice or "best" practice to apply in my case? Thanks on advance, Serhiy.

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• Clean way in GWT/Java to wait for multiple asynchronous events to finish

  - by gerdemb

  What is the best way to wait for multiple asynchronous callback functions to finish in Java before continuing. Specifically I'm using GWT with AsyncCallback, but I think this is a generic problem. Here's what I have now, but surely there is cleaner way... AjaxLoader.loadApi("books", "0", new Runnable(){ public void run() { bookAPIAvailable = true; ready(); }}, null); AjaxLoader.loadApi("search", "1", new Runnable(){ public void run() { searchAPIAvailable = true; ready(); }}, null); loginService.login(GWT.getHostPageBaseURL(), new AsyncCallback<LoginInfo>() { public void onSuccess(LoginInfo result) { appLoaded = true; ready(); } }); private void ready() { if(bookAPIAvailable && searchAPIAvailable && appLoaded) { // Everything loaded } }

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• javasrcipt asyncronous function

  - by Ben

  Hi there, i have a problem understanding how this could/should be solved. I have two functions. In the first function ( I call it loadData() ) I'm doing an asyncronous request to the server to load some data. In the second function ( saveData() ) I'm also doing an asyn request to the server to write some data. In the callback of this request I'm callin loadData() to refresh the data. Now the problem: In the saveData() function I want to wait for loadData() to be finished bevore I show a dialog (like alert('Data saved')) I guess this is a common problem, but I couldn't find the solution for it (if there is one..) A solution would be to make the requests syncronous, but the framework I'm using doesn't offer that and I hope there's a better solution.. Thanks to all!

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• Which JavaScript Libraries do not rely on a document and navigator object?

  - by Julian Weimer

  I'm currently looking for some libraries which might help me during iPhone Development using Appcelerator Titanium. I've heard that since version 1.0 it isn't dependant on webkit anymore and it makes app-development more exiting of course, please correct me if i'm wrong. As many people out there i love Javascript Frameworks such as JQuery and Mootools much, but they were build specifically to do a great job within a browser and most of the functionality is not needed within the environment Titanium now provides (DOM-Manipulation etc). Is there any other small library of useful functions i can use for development? Thx in advance.

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• Validate decimal number in (known) national format

  - by Álvaro G. Vicario

  PHP has many built-in functions to validate numbers but they all expect input in computer format: 1234.56. I need to validate stuff like 1,234.56 (English) or 1.234,56 (Spanish), together with some typical attributes (accepted range, max number of decimals, etc.). I started writing my own function but I soon got lost. It's easy to read the user input into a float variable but I want to be able to detect numbers with invalid formats like 1,23456.7 or 1..25. Do you have any recommendation on the subject? (Decimal and thousand characters are known beforehand and it's okay to hard-code digit groups as three, there's no need to cover Indian number format.)

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• Passing HTML using JSON

  - by ActionFactory

  Hi All, I'm passing Data using JSON to iPhone and iPad. One Field of Data is HTML. The problem is the encoding. Here's what I get back: > "GadgetHTML": "<strong>Hello</strong> > from Catworld<br />\n<img alt=\"\" > src=\"http://www.iconarchive.com/icons/fasticon/ifunny/128/dog-icon.png\" > />", The \ are killing me. The \n does not help. Any good way to do this? Any JSON to HTML Cleaning Functions? Encoding? (There must be something better than manually removing ) Thanks

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• Storing expression template functors

  - by UncaughtException

  Hello guys, at the moment I'm really interested in expression templates and want to code a library for writing and differentiating mathematical functions with a lambda-style syntax. At the moment, I'm able to write (_x * _x)(2); and get the correct result 4. But I would really like to do something like MathFunction f = _x * _x; f(2);, but I don't have any ideas on how to cope with the recursive expression templates on the right side. Is it possible to achieve this without using the 'auto'-Keyword instead of MathFunction or having to make the operator() virtual? Thanks for your help!

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