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• Calling C++ function from C.

  - by claws

  I know this. Calling C function from C++: If my application was in C++ and I had to call functions from a library written in C. Then I would have used //main.cpp extern "C" void C_library_function(int x, int y);//prototype C_library_function(2,4);// directly using it. This wouldn't mangle the name C_library_function and linker would find the same name in its input *.lib files and problem is solved. Calling C++ function from C??? But here I'm extending a large application which is written in C and I need to use a library which is written in C++. Name mangling of C++ is causing trouble here. Well I cannot use C++ compiler over my C project because thats breaking lot of other stuff. What is the way out? By the way I'm using MSVC

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• ASP.NET Radio Button State and Back Key

  - by Dave S

  When using the browser back key on a page with radio buttons and using auto-postback, the state of the buttons (checked) stays the same while other parts of the page do not. This results in a situation where button two is checked and the cached page (because of server-side logic) displays a message that button 1 is checked. What is the best way to handle this situation? The following code example exhibits this behavior: [Form:] <asp:RadioButton ID="rb1" runat="server" AutoPostBack="true" Text="Button1" OnCheckedChanged="rb_CheckedChanged" GroupName="rbgroup" Checked="true" /> <br /> <asp:RadioButton ID="rb2" runat="server" AutoPostBack="true" Text="Button2" OnCheckedChanged="rb_CheckedChanged" GroupName="rbgroup" /> <br /> <hr /> <asp:Label ID="lbl1" runat="server">Button 1</asp:Label> [Code Behind:] protected void rb_CheckedChanged(object sender, EventArgs e) { if (rb1.Checked == true) lbl1.Text = "Button 1"; else lbl1.Text = "Button 2"; }

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• can a program written in C be faster than one written in OCaml and translated to C?

  - by Ole Jak

  So I have some cool Image Processing algorithm. I have written it in OCaml. It performs well. I now I can compile it as C code with such command ocamlc -output-obj -o foo.c foo.ml (I have a situation where I am not alowed to use OCaml compiler to bild my programm for my arcetecture, I can use only specialy modified gcc. so I will compile that programm with sometyhing like gcc -L/usr/lib/ocaml foo.c -lcamlrun -lm -lncurses and Itll run on my archetecture.) I want to know in general case can a program written in C be faster than one written in OCaml and translated to C?

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• Same memory space being allocated again & again while using malloc()

  - by shadyabhi

  In each loop iteration, variable j is declared again and again. Then why is its address remaining same? Shouldn't it be given some random address each time? Is this compiler dependent? #include<stdio.h> #include<malloc.h> int main() { int i=3; while (i--) { int j; printf("%p\n", &j); } return 0; } Testrun:- shadyabhi@shadyabhi-desktop:~/c$ gcc test.c shadyabhi@shadyabhi-desktop:~/c$ ./a.out 0x7fffc0b8e138 0x7fffc0b8e138 0x7fffc0b8e138 shadyabhi@shadyabhi-desktop:~/c$

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• How to Print reports in Silvelright 4

  - by lightmeetsdark

  I am wondering if there is anything built in to Silverlight, or possibly c# to allow for printing reports? I'd be happy with any number of methods: exporting files to a pdf format and printing from there, exporting as a text document of some sort and printing from there, or just simply showing the print dialog from the web application itself. I know there are ways to do this in C#, but the c# code-behind is different for many things in Silverlight applications and I can't seem to find anything that will work. So if anyone has any ideas on things I could try it would be very much appreciated! Thank you!

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• [FLEX 3] Placing images into a Collage Canvas

  - by Bridget

  I've got an array of different sized images. I want to place these images on a canvas in a sort of automated collage. Does anyone have an idea of how to work the logic behind this concept? All my images have heights divisible by 36 pixels and widths divisible by 9 pixels. They have mouseDown functions that allow you to drag and drop. When dropped the image goes to the closest x point divisible by 9 and y point divisble by 36. There is a grid drawn on top of the canvas. I've sorted the array of images based on height, then based on their widths. imagesArray.sortOn("height", Array.NUMERIC | Array.DESCENDING); imagesArray.sortOn("width", Array.NUMERIC | Array.DESCENDING); I'd like to take the largest image ( imageArray[0] ) to put in corner x,y = 0,0. Then randomize the rest of the images and fit them into the collage canvas.

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• Best way to access nested data structures?

  - by Blackshark

  I would like to know what the best way (performance wise) to access a large data structure is. There are about hundred ways to do it but what is the most accessible for the compiler to optimize? One can access a value by foo[someindex].bar[indexlist[i].subelement[j]].baz[0] or create some pointer aliases like sometype_t* tmpfoo = &foo[someindex]; tmpfoo->bar[indexlist[i].subelement[j]].baz[0] or create reference aliases like sometype_t &tmpfoo = foo[someindex]; tmpfoo.bar[indexlist[i].subelement[j]].baz[0] and so forth...

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• Why I have to redeclare a virtual function while overriding [C++]

  - by Neeraj

  #include <iostream> using namespace std; class Duck { public: virtual void quack() = 0; }; class BigDuck : public Duck { public: // void quack(); (uncommenting will make it compile) }; void BigDuck::quack(){ cout << "BigDuckDuck::Quack\n"; } int main() { BigDuck b; Duck *d = &b; d->quack(); } Consider this code, the code doesn't compiles. However when I declare the virtual function in the subclass, then it compiles fine. The compiler already has the signature of the function which the subclass will override, then why a redeclaration is required? Any insights.

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• How to use AOP to intercept a method call in super on an argument?

  - by hleinone

  I'm extending a class and overriding a method. All I want to do is to call super, but with a modified argument that gets intercepted upon one of its methods is called. An example makes it more clear: // Foo is an interface and also this method is part of an interface @Override public void foo(Foo foo) { // I want to intercept the call to foo.bar() in super super.foo(foo); } I'd rather use a tool that doesn't require a compiler of its own. What would be the optimal one?

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• Problem using a costum server control in a aspx

  - by gre3ns0ul

  Hi guys, i am having a issue. I already developed one class (my custom gridview) and i want use it on a .aspx That class is defined in app_code and compiled to the dll of the project. namespace MyCostumControls{  public class DropDownPagingGridView : GridView{ ... I already registered the control on the aspx page using <%@ Register Namespace="MyCostumControls" TagPrefix="ctrl" % and i can use in the page and works ok.. But i'm watching one problem. That class contains methods defined by me, than when i try to call them in code-behind sayd to me than they're not defined. In designed i don't see the reference to MyCostumControls, and when i try declare one field using protected global::MyCostumControls.MyCostumControls ddl_gv_errors, i cannot access to MyCostumControls namespace, Is because he's compiled to the project dll? I can access to all namespaces than are not contained in app_code. Solutions? Apreciate. Thanks

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• int vs const int&

  - by Valdo

  I've noticed that I usually use constant references as return values or arguments. I think the reason is that it works almost the same as using non-reference in the code. But it definitely takes more space and function declarations become longer. I'm OK with such code but I think some people my find it a bad programming style. What do you think? Is it worth writing const int& over int? I think it's optimized by the compiler anyway, so maybe I'm just wasting my time coding it, a?

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• Why does a non-constant offsetof expression work?

  - by Chris J. Kiick

  Why does this work: #include <sys/types.h> #include <stdio.h> #include <stddef.h> typedef struct x { int a; int b[128]; } x_t; int function(int i) { size_t a; a = offsetof(x_t, b[i]); return a; } int main(int argc, char **argv) { printf("%d\n", function(atoi(argv[1]))); } If I remember the definition of offsetof correctly, it's a compile time construct. Using 'i' as the array index results in a non-constant expression. I don't understand how the compiler can evaluate the expression at compile time. Why isn't this flagged as an error?

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• How to convert server time to local time?

  - by Lost_in_code

  My php file is hosted in some other part of the world. The date() and time() functions returns the date/time on the server. How do I convert that date so that it's the same as my local date/time? The date on the server is 10 hours behind my local time. I could just hard code and substract this from the server time. But what is the proper way of going about this so that no value has to be hardcoded?

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• Using an int as the numerical representation of a string in C#

  - by bluewall21

  I'm trying to use an integer as the numerical representation of a string, for example, storing "ABCD" as 0x41424344. However, when it comes to output, I've got to convert the integer back into 4 ASCII characters. Right now, I'm using bit shifts and masking, as follows: int value = 0x41424344; string s = new string ( new char [] { (char)(value >> 24), (char)(value >> 16 & 0xFF), (char)(value >> 8 & 0xFF), (char)(value & 0xFF) }); Is there a cleaner way to do this? I've tried various casts, but the compiler, as expected, complained about it.

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• Assigning Value to a variable that is too big for it! (checked and unchecked concept)

  - by ThickBook

  So when we assign a value to a variable then that variable should be able to hold it, right? and if not compiler produces the error. Now there is an option in C# known as Checked (which is by default) and unchecked option. But is there practical use of unchecked? any comments for a layman? :) Example: int a=int.MaxValue; int b=int.MaxValue; unchecked { int sum=a+b; }

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• Strange macro declaration in C

  - by Andrey Atapin

  Exploring libusb-1.0.9 source code, I have found such line (./os/poll_windows.c:78): #define CHECK_INIT_POLLING do {if(!is_polling_set) init_polling();} while(0) As for me this is the same like: #define CHECK_INIT_POLLING if(!is_polling_set) init_polling(); Is there any reason to loop that expression? UPDATE: I couldn't still realize what'd be wrong after the answers, and the following example helped: #include <stdio.h> #define TEST if(test) foo(); #define TEST_DO do { if(test) foo(); } while(0) int test = 1; void foo() { printf("%s", "Foo called"); } int main(int argc, char** argv) { if(argc > 1) TEST_DO; /* LINE 12 */ else printf("%s", "skipping..."); return 0; } If you put TEST at line 12, a compiler will give an error "error: ‘else’ without a previous ‘if’". Hope, this will help someone.

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• Java generic Interface performance

  - by halfwarp

  Simple question, but tricky answer I guess. Does using Generic Interfaces hurts performance? Example: public interface Stuff<T> { void hello(T var); } vs public interface Stuff { void hello(Integer var); <---- Integer used just as an example } My first thought is that it doesn't. Generics are just part of the language and the compiler will optimize it as though there were no generics (at least in this particular case of generic interfaces). Is this correct?

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• How do you get GWT 2.0 to accept clicks on two different Widgets added to a LayoutPanel?

  - by kerrr

  Using GWT 2.0 I have an entry point that adds two Widgets to a LayoutPanel. The Widgets both handle click events and have click events ergistered to them. The problem is that only the last widget added to the LayoutPanel can actually be clicked. Switch the order in which the widgets are added switches the widget that works. Add mroe widgets and still the only you can click is the last one added to the LayoutPanel. Any idea why this is? Is there any reasoning behind the behaviour, or have I missunderstood what is happening under the covers? How do I gat all widgets in the LayoutPanel to accept events? Should I be using another panel class? I'm not too bothered if the LayoutPanel prevents anything below it from being clicked, but want all Widgets added to it to be clickable.

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• Create object of unknown class (two inherited classes)

  - by Paul

  I've got the following classes: class A { void commonFunction() = 0; } class Aa: public A { //Some stuff... } class Ab: public A { //Some stuff... } Depending on user input I want to create an object of either Aa or Ab. My imidiate thought was this: A object; if (/*Test*/) { Aa object; } else { Ab object; } But the compiler gives me: error: cannot declare variable ‘object’ to be of abstract type ‘A’ because the following virtual functions are pure within ‘A’: //The functions... Is there a good way to solve this?

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• assignment from incompatible pointer type

  - by Hristo

  I have set up the following struct: typedef struct _thread_node_t { pthread_t thread; struct thread_node_t *next; } thread_node_t; ... and then I have defined: // create thread to for incoming connection thread_node_t *thread_node = (thread_node_t*) malloc(sizeof(thread_node_t)); pthread_create(&(thread_node->thread), NULL, client_thread, &csFD); thread_node->next = thread_arr; // assignment from incompatible pointer type thread_arr = thread_node; where thread_arr is thread_node_t *thread_arr = NULL; I don't understand why the compiler is complaining. Maybe I'm misunderstanding something.

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• Fastest method for SQL Server inserts, updates, selects

  - by Ian

  I use SPs and this isn't an SP vs code-behind "Build your SQL command" question. I'm looking for a high-throughput method for a backend app that handles many small transactions. I use SQLDataReader for most of the returns since forward only works in most cases for me. I've seen it done many ways, and used most of them myself. Methods that define and accept the stored procedure parameters as parameters themselves and build using cmd.Parameters.Add (with or without specifying the DB value type and/or length) Assembling your SP params and their values into an array or hashtable, then passing to a more abstract method that parses the collection and then runs cmd.Parameters.Add Classes that represent tables, initializing the class upon need, setting the public properties that represent the table fields, and calling methods like Save, Load, etc I'm sure there are others I've seen but can't think of at the moment as well. I'm open to all suggestions.

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• cygwin g++ produces no output

  - by fred basset

  I just installed g++ from cygwin, when I try to compile a C++ file I am not getting any executable produced by the compiler, see example below. What's going wrong? Directory of C:\helloworld 01/02/2011 04:50 PM . 01/02/2011 04:50 PM .. 01/02/2011 04:48 PM 94 helloworld.cpp 1 File(s) 94 bytes 2 Dir(s) 24,658,272,256 bytes free C:\helloworldg++-4 helloworld.cpp C:\helloworlddir Volume in drive C is OS Volume Serial Number is C47B-942D Directory of C:\helloworld 01/02/2011 04:50 PM . 01/02/2011 04:50 PM .. 01/02/2011 04:48 PM 94 helloworld.cpp 1 File(s) 94 bytes 2 Dir(s) 24,657,747,968 bytes free C:\helloworld

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• Is there a TextWriter interface to the System.Diagnostics.Debug class?

  - by John Källén

  I'm often frustrated by the System.Diagnostics.Debug.Write/WriteLine methods. I would like to use the Write/WriteLine methods familiar from the TextWriter class, so I often write Debug.WriteLine("# entries {0} for connection {1}", countOfEntries, connection); which causes a compiler error. I end up writing Debug.WriteLine(string.Format("# entries {0} for connection {1}", countOfEntries, connection)); which is really awkward. Does the CLR have a class deriving from TextWriter that "wraps" System.Debug, or should I roll my own?

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• Can I reproduce Scala's behavior for == ?

  - by JPP

  In Programming in Scala, I can read that the == operator behaves as if it was defined like this: final def == (that: Any): Boolean = if (null eq this) {null eq that} else {this equals that} But there must actually be compiler magic to avoid null pointer exceptions, right? Is there any way for me to replicate this behavior with pure Scala; i.e., have an operator/method return one thing if the receiver is null and another one if it isn't? What I mean is an actual implementation of null eq this. I suppose I can write a "pimp" and then define the method on the wrapper class, but is there a more direct way to do this?

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• Same memory space being allocated again & again

  - by shadyabhi

  In each loop iteration, variable j is declared again and again. Then why is its address remaining same? Shouldn't it be given some random address each time? Is this compiler dependent? #include<stdio.h> #include<malloc.h> int main() { int i=3; while (i--) { int j; printf("%p\n", &j); } return 0; } Testrun:- shadyabhi@shadyabhi-desktop:~/c$ gcc test.c shadyabhi@shadyabhi-desktop:~/c$ ./a.out 0x7fffc0b8e138 0x7fffc0b8e138 0x7fffc0b8e138 shadyabhi@shadyabhi-desktop:~/c$

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