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• How does the destructor know when to activate itself? Can it be relied upon?

  - by Robert Mason

  Say for example i have the following code (pure example): class a { int * p; public: a() { p = new int; ~a() { delete p; } }; a * returnnew() { a retval; return(&retval); } int main() { a * foo = returnnew(); return 0; } In returnnew(), would retval be destructed after the return of the function (when retval goes out of scope)? Or would it disable automatic destruction after i returned the address and i would be able to say delete foo; at the end of main()? Or, in a similar vein (pseudocode): void foo(void* arg) { bar = (a*)arg; //do stuff exit_thread(); } int main() { while(true) { a asdf; create_thread(foo, (void*)&asdf); } return 0; } where would the destructor go? where would i have to say delete? or is this undefined behavior? Would the only possible solution be to use the STL referenced-counted pointers? how would this be implemented? Thank you- i've used C++ for a while but never quite been in this type of situation, and don't want to create memory leaks.

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• Why does my custom component raise AVs in the IDE?

  - by Mason Wheeler

  I'm trying to write a simple component that will allow you to embed one or more SDL rendering surfaces on a Delphi window, using the SDL 1.3 APIs. It will compile and install just fine, but when I try to use the component in the form designer, it raises AVs whenever I try to access its properties in the object inspector, save the form, or delete the component, and placing one on a form then trying to run gives a linker error: it apparently can't read the DFM properly for whatever reason. The DLL can be found at http://www.libsdl.org/tmp/SDL-1.3-dll.zip and the source code to my component can be downloaded here. SDL.pas is a JEDI-SDL header file; the rest is my own code. I don't see any reason for this to raise AVs in the form designer. If I dynamically create the control at runtime I don't have any stability issues. Can anyone take a look at this and maybe provide some feedback that might help me clear it up?

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• How do I get the current color of a fragment?

  - by Mason Wheeler

  I'm trying to wrap my head around shaders in GLSL, and I've found some useful resources and tutorials, but I keep running into a wall for something that ought to be fundamental and trivial: how does my fragment shader retrieve the color of the current fragment? You set the final color by saying gl_FragColor = whatever, but apparently that's an output-only value. How do you get the original color of the input so you can perform calculations on it? That's got to be in a variable somewhere, but if anyone out there knows its name, they don't seem to have recorded it in any tutorial or documentation that I've run across so far, and it's driving me up the wall.

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• How do I read an arbitrary chunk from a PNG file?

  - by Mason Wheeler

  I've got some custom metadata to put into a PNG file. It's being saved through libpng, and it's not difficult to write out a custom chunk. I just call png_write_chunk with the name, length and data. But I can't see how to get the data back out again. I'd expect there to be a png_read_chunk function that takes a chunk name and returns a pointer to the data or something like that, but there's nothing like that in png.h. Does anyone know how to accomplish this?

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• Biggest Delphi nitpicks

  - by Mason Wheeler

  What sort of minor annoyances do you run into using Delphi? I'm not looking for major issues such as "I want a 64-bit compiler." Just little things that can be easily worked around but still should have been implemented better so you don't have to work around them? Marking this CW. I'm more interested in the answers than the points.

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• How do I make lines scale when using GLOrtho?

  - by Mason Wheeler

  I'm using GLOrtho to set up a 2D view that I can render textures onto. It works really well, up until I try to zoom in on the image. If I pass half the width and half the height of the viewport to GLOrtho, I end up with all my textures displayed twice as big as normal, which is exactly what I expect. But then I try to draw a box around part of the image and it all falls apart. I call glBegin(GL_LINE_LOOP), place the four vertices, and call glEnd, and I expect to see the same thing I would see if I drew it at normal zoom level, doubled. Instead, I get lines that are all the right length, but they all come out one pixel wide, instead of two, and it looks really bad. What am I missing?

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• How to know when my control changes size?

  - by Mason Wheeler

  I'm building a custom control, and I need it to be able to respond when it gets resized. I need the old dimensions and the new dimensions available in order to do some calculations. Unfortunately, the SetWidth and SetHeight methods are private to TControl, not protected, and so I can't override them. Is there any other way to know that my control's about to be resized, and to have the old size and the new size both available?

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• Anyone know how to use TValue.AsType<TNotifyEvent> properly?

  - by Mason Wheeler

  I'm trying to use RTTI to add an event handler to a control, that may already have an event handler set. The code looks something like this: var prop: TRttiProperty; val: TValue; begin prop := FContext.GetType(MyControl.ClassInfo).GetProperty('OnChange'); val := prop.GetValue(MyControl); FOldOnChange := val.AsType<TNotifyEvent>; prop.SetValue(MyControl, TValue.From<TNotifyEvent>(self.MyOnChange)); end; I want this so I can do this in MyOnChange: begin if assigned(FOldOnChange) then FOldOnChange(Sender); //additional code here end; Unfortunately, the compiler doesn't seem to like the line FOldOnChange := val.AsType<TNotifyEvent>;. It says E2010 Incompatible types: 'procedure, untyped pointer or untyped parameter' and 'TNotifyEvent' Anyone know why that is or how to fix it? It looks right to me...

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• How to publish a list of integers?

  - by Mason Wheeler

  I want to make a component that includes a list of integers as one of its serialized properties. I know I can't declare a TList<integer> as a published property, because it doesn't descend from TPersistent. I've read that you can define "fake" published properties if you override DefineProperties, but I'm not quite sure how that works, especially when it comes to creating a fake property that's a list, not a single value. Can someone point me in the right direction?

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• Can I get a PTypeInfo from a string?

  - by Mason Wheeler

  This is probably going to be a "no", but is there any way I can use Delphi's RTTI, either old-school or the 2010 extended RTTI, to pass in a string containing the name of a type, specifically the name of an enumerated type, and have it give me the PTypeInfo for that type? I've looked through RTTI.pas and TypInfo.pas and I don't see any function that would do that, but I might have missed something. What I'm looking for: var info: PTypeInfo; begin info := GetTypeInfoFromName('TComponentStyle'); end; Or something like that. Thing is, the name of the enumerated type would be passed in; it wouldn't be known at compile time.

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• How do I retrieve an automated report and save it to a database?

  - by Mason Wheeler

  I've got a web server that will take scripts in Python, PHP or Perl. I don't know much about any of those languages, but of the three, Python seems the least scary. It has a MySql database set up, and I know enough SQL to manage it and write queries for it. I also have a program that I want to add automated error reporting to. Something goes wrong, it sends a bug report to my server. What I don't know how to do is write a Python script that will sit on the web server and, when my program sends in a bug report, do the following: Receive the bug report. Parse it out into sections. Insert it into the database. Have the server send me an email. From what little I understand, this seems like it shouldn't be too difficult if I only knew what I was doing. Could someone point me to a site that explains the basic principles I'd need to create a script like this?

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• Is there any way to run "dir" directly?

  - by Mason Wheeler

  In my answer to this question, where the asker needed a fast way to get a directory listing of a folder on a network drive, I suggested using the DOS "dir" command. Unfortunately, it's a command, not a program, so you can't execute it with CreateProcess and so I had to put it in a batch file. I don't really like that solution. It feels like a hack to me. Does anyone know a way to run dir from Delphi instead of from an external batch file?

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• Avoiding "variable might not have been initialized"

  - by Mason Wheeler

  I recently ran across a routine that looks something like this: procedure TMyForm.DoSomething(list: TList<TMyObject>; const flag: boolean); var local: integer; begin if flag then //do something else local := ExpensiveFunctionCallThatCalculatesSomething; //do something else for i := 0 to list.Count do if flag then //do something else if list[i].IntValue > local then //WARNING HERE //do something else end; This gives Variable 'local' might not have been initialized even though you can tell by reading the code that you won't hit that line unless the code branch that initializes it has run. Now, I could get rid of this warning by adding a useless local := 0; at the top of the procedure, but I wonder if there might not be a better way to structure this to avoid the issue. Anyone have any ideas?

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• Is there a way to programatically check dependencies of an EXE?

  - by Mason Wheeler

  I've got a certain project that I build and distribute to users. I have two build configurations, Debug and Release. Debug, obviously, is for my use in debugging, but there's an additional wrinkle: the Debug configuration uses a special debugging memory manager, with a dependency on an external DLL. There's been a few times when I've accidentally built and distributed an installer package with the Debug configuration, and it's then failed to run once installed because the users don't have the special DLL. I'd like to be able to keep that from happening in the future. I know I can get the dependencies in a program by running Dependency Walker, but I'm looking for a way to do it programatically. Specifically, I have a way to run scripts while creating the installer, and I want something I can put in the installer script to check the program and see if it has a dependency on this DLL, and if so, cause the installer-creation process to fail with an error. I know how to create a simple CLI program that would take two filenames as parameters, and could run a DependsOn function and create output based on the result of it, but I don't know what to put in the DependsOn function. Does anyone know how I'd go about writing it?

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• Making a table in a scrolling div resizable?

  - by Mason Jones

  I've got a table in a div, with a vertical scrollbar on the div to allow the table to be longer than the div can hold. Works fine. But I'd like to allow the user to resize the div vertically if they want to be able to view more of the table. I've been playing with the jQueryUI resizable interaction, but it doesn't seem to quite do what I want; at least, not so far. I've tried making the wrapper div resizable, but the behavior's erratic. If I have the style "height:20em; overflow:auto;" on it, then I can resize the table horizontally, but not vertically. If I remove the overflow, then the table flows outside the div of course. If I remove the height, then the table is actually resizable, but it is initially drawn at full height. Anyone know of a way to specify an initial height, but allow it to be resized larger than that? If I make the table resizable rather than the div, then I can resize the table horizontally within the div but I can't increase the height of the displayed table. Which makes sense, of course, but I thought I'd mention it. Also, is there a way to make the resize "handle" the corner between the horizontal and vertical scrollbars? Right now it's a sort of invisible handle in the bottom-right of the table. Thanks for any thoughts.

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• How do I make VC++'s debugger break on exceptions?

  - by Mason Wheeler

  I'm trying to debug a problem in a DLL written in C that keeps causing access violations. I'm using Visual C++ 2008, but the code is straight C. I'm used to Delphi, where if an exception occurs while running under the debugger, the program will immediately break to the debugger and it will give you a chance to examine the program state. In Visual C++, though, all I get is a message in the Output tab: First-chance exception at blah blah blah: Access violation reading location 0x04410000. No breaks, nothing. It just goes and unwinds the stack until it's back in my Delphi EXE, which recognizes something's wrong and alerts me there, but by that point I've lost several layers of call stack and I don't know what's going on. I've tried other debugging techniques, but whatever it's doing is taking place deep within a nested loop inside a C macro that's getting called more than 500 times, and that's just a bit beyond my skill (or my patience) to trace through. I figure there has to be some way to get the "first-chance" exception to actually give me a "chance" to handle it. There's probably some "break immediately on first-chance exceptions" configuration setting I don't know about, but it doesn't seem to be all that discoverable. Does anyone know where it is and how to enable it?

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• Does anyone know how to register VC++ Express 2008?

  - by Mason Wheeler

  I recently reinstalled Visual C++ 2008 Express after a system crash, and now it wants me to register. But when I go to the registration page, all I get is information about registering VS Express 2010, which is not what I'm trying to do. Does anyone know if it's still possible to register VS Express 2008?

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• Draggable tab control for Delphi?

  - by Mason Wheeler

  Are there any tab controls available for Delphi where the tabs can be clicked and dragged to reorder them, like in a web browser?

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• Constructor Type Coercion in C++

  - by Robert Mason

  Take the following class: class mytype { double num; public: mytype(int a) { num = sqrt(a); } void print() { cout << num; } } Say there is a method which takes a mytype: void foo(mytype a) { a.print(); } Is it legal c++ (or is there a way to implement this) to call foo(4), which would (in theory) output 2? From what I can glean you can overload type casts from a user defined class, but not to. Can constructor do this in a standards-compliant manner (assuming, of course, the constructor is not explicit). Hopefully there is a way to in the end have this legal: int a; cin >> a; foo(a); Note: this is quite obviously not the actual issue, but just an example for posting purposes. I can't just overload the function because of inheritance and other program-specific issues.

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• Performance characteristics of pthreads vs ucontext

  - by Robert Mason

  I'm trying to port a library that uses ucontext over to a platform which supports pthreads but not ucontext. The code is pretty well written so it should be relatively easy to replace all the calls to the ucontext API with a call to pthread routines. However, does this introduce a significant amount of additional overhead? Or is this a satisfactory replacement. I'm not sure how ucontext maps to operating system threads, and the purpose of this facility is to make coroutine spawning fairly cheap and easy. So, question is: Does replacing ucontext calls with pthread calls significantly change the performance characteristics of a library?

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• Is there a Delphi standard function for escaping HTML?

  - by Mason Wheeler

  I've got a report that's supposed to take a grid control and produce HTML output. One of the columns in the grid can display any of a number of values, or <Any>. When this gets output to HTML, of course, it ends up blank. I could probably write up some routine to use StringReplace to turn that into &lt;Any&gt; so it would display this particular case correctly, but I figure there's probably one in the RTL somewhere that's already been tested and does it right. Anyone know where I could find it?

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• How do I override methods of nested types?

  - by Mason Wheeler

  I've got a custom TObjectList descendant in Delphi 2009, and I'd like to play with its enumerator a bit and add some filtering functionality to the MoveNext method, to cause it to skip certain objects. MoveNext is called by DoMoveNext, which is a virtual method, so this shouldn't be difficult to override... except for one thing. The TEnumerator for TObjectList isn't its own class; it's declared as a nested type within the TObjectList declaration. Is there any simple way to override TEnumerator.DoMoveNext in my descendant class, or do I have to reimplement the whole TEnumerator? It's not a very big class, but I'd prefer to keep redundancies to a minimum if I can...

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• Can sorting Japanese kanji words be done programatically?

  - by Mason

  I've recently discovered, to my astonishment (having never really thought about it before), machine-sorting Japanese proper nouns is apparently not possible. I work on an application that must allow the user to select a hospital from a 3-menu interface. The first menu is Prefecture, the second is City Name, and the third is Hospital. Each menu should be sorted, as you might expect, so the user can find what they want in the menu. Let me outline what I have found, as preamble to my question: The expected sort order for Japanese words is based on their pronunciation. Kanji do not have an inherent order (there are tens of thousands of Kanji in use), but the Japanese phonetic syllabaries do have an order: ???????????????????... and on for the fifty traditional distinct sounds (a few of which are obsolete in modern Japanese). This sort order is called ???? (gojuu on jun , or '50-sound order'). Therefore, Kanji words should be sorted in the same order as they would be if they were written in hiragana. (You can represent any kanji word in phonetic hiragana in Japanese.) The kicker: there is no canonical way to determine the pronunciation of a given word written in kanji. You never know. Some kanji have ten or more different pronunciations, depending on the word. Many common words are in the dictionary, and I could probably hack together a way to look them up from one of the free dictionary databases, but proper nouns (e.g. hospital names) are not in the dictionary. So, in my application, I have a list of every prefecture, city, and hospital in Japan. In order to sort these lists, which is a requirement, I need a matching list of each of these names in phonetic form (kana). I can't come up with anything other than paying somebody fluent in Japanese (I'm only so-so) to manually transcribe them. Before I do so though: Is it possible that I am totally high on fire, and there actually is some way to do this sorting without creating my own mappings of kanji words to phonetic readings, that I have somehow overlooked? Is there a publicly available mapping of prefecture/city names, from the government or something? That would reduce the manual mapping I'd need to do to only hospital names. Does anybody have any other advice on how to approach this problem? Any programming language is fine--I'm working with Ruby on Rails but I would be delighted if I could just write a program that would take the kanji input (say 40,000 proper nouns) and then output the phonetic representations as data that I could import into my Rails app. ??????????

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• Closing a window when it's "no longer needed".

  - by Mason Blier

  This is kind of a hard question to describe, and I've searched for about an hour now to no avail. Essentially, picture a small 'flyout' window like the Windows 7 Wireless Control or the Volume Slider from the system tray(notification area). When you click on the icon, the application pops up with focus, and if you click off of it, the window destroys itself. I thought it woudl be easily solved by simply having my window destroy it self when it loses focus (I've been listening for WM_KILLFOCUS), but the problem is, if the icon is clicked, my window does not always get focus. Since this isn't the case, if the user clicks my icon, and then clicks away because it was a mistake (on the desktop say), then how can I set my app to close? I've tried messing with SPY++ but checking the volume control / wireless control apps are proving difficult as they disappear when I try to get their window/process handles. Thanks!

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• WSACONNREFUSED when connecting to server

  - by Robert Mason

  I'm currently working on a server. I know that the client side is working (I can connect to www.google.com on port 80, for example), but the server is not functioning correctly. The socket has socket()ed, bind()ed, and listen()ed successfully and is on an accept loop. The only problem is that accept() doesn't seem to work. netstat shows that the server connection is running fine, as it prints the PID of the server process as LISTENING on the correct port. However, accept never returns. Accept just keeps running, and running, and if i try to connect to the port on localhost, i get a 10061 WSACONNREFUSED. I tried looping the connection, and it just keeps refusing connections until i hit ctrl+c. I put a breakpoint directly after the call to accept(), and no matter how many times i try to connect to that port, the breakpoint never fires. Why is accept not accepting connections? Has anyone else had this problem before? Known: [breakpoint0] if ((new_fd = accept(sockint, NULL, NULL)) == -1) { throw netlib::error("Accept Error"); //netlib::error : public std::exception } else { [breakpoint1] code...; } breakpoint0 is reached (and then continued through), no exception is thrown, and breakpoint1 is never reached. The client code is proven to work. Netstat shows that the socket is listening. If it means anything, i'm connecting to 127.0.0.1 on port 5842 (random number). The server is configured to run on 5842, and netstat confirms that the port is correct.

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