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• Are there any Python reference counting/garbage collection gotchas when dealing with C code?

  - by Jason Baker

  Just for the sheer heck of it, I've decided to create a Scheme binding to libpython so you can embed Python in Scheme programs. I'm already able to call into Python's C API, but I haven't really thought about memory management. The way mzscheme's FFI works is that I can call a function, and if that function returns a pointer to a PyObject, then I can have it automatically increment the reference count. Then, I can register a finalizer that will decrement the reference count when the Scheme object gets garbage collected. I've looked at the documentation for reference counting, and don't see any problems with this at first glance (although it may be sub-optimal in some cases). Are there any gotchas I'm missing? Also, I'm having trouble making heads or tails of the cyclic garbage collector documentation. What things will I need to bear in mind here? In particular, how do I make Python aware that I have a reference to something so it doesn't collect it while I'm still using it?

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• Problem of using cin twice.

  - by gc

  Here is the code: string str; cinstr; cout<<"first input:"<<str<<endl; getline(cin, str); cout<<"line input:"<<str<<endl; The result is that getline never pauses for user input, therefore the second output is always empty. After spending some time on it, I realized after the first call "cinstr", it seems '\n' is still stored in cin (using cin.peek() to check), which ends getline immediately. The solution will be adding one more line between the first usage and the second one: cin.ignore(numeric_limits::max(), '\n'); However, I still don't understand, why is '\n' left there after the first call? What does istream& operator really do?

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• Class inheriting from several Interfaces having same method signature

  - by Manish

  Say, I have three interfaces: public interface I1 { void XYZ(); } public interface I2 { void XYZ(); } public interface I3 { void XYZ(); } A class inheriting from these three interfaces: class ABC: I1,I2, I3 { // method definitions } Questions: If I implement like this: class ABC: I1,I2, I3 { public void XYZ() { MessageBox.Show("WOW"); } } It compiles well and runs well too! Does it mean this single method implementation is sufficient for inheriting all the three Interfaces? How can I implement the method of all the three interfaces and CALL THEM? I know it can done using explicit implementation but I'm not able to call them. :(

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• GCC/XCode equivalent of _CrtCheckMemory?

  - by Chris Becke

  When dealing with random memory overwrites, in MSVC it is possible to validate the state of the heap at various points with a call to _CrtCheckMemory, and know with at least a small level of confidence that the code up until the check was not responsible for any errors that might cause new or malloc to fail later. In XCode, whats the equivalent way to try and box in a memory overwrite? All I have at the moment is a random failure of a call to new, somewhere deep in the bowels of some code with no real idea of how long the code has been running with a corrupt heap up until that point.

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• Why I get java.net.SocketException: Connection reset

  - by Jammy

  I need sent some requests to server side and get reponse, sometimes when I call specific method to run the flollowing common code, I get one error in line(addToCookieJar(connection);), any idea how this get happened? URL url = new URL(providerURL); HttpURLConnection connection = (HttpURLConnection)url.openConnection(); connection.setRequestMethod("POST"); connection.setDoInput(true); connection.setDoOutput(true); connection.setUseCaches(false); connection.setRequestProperty("Content-Type", "application/octet-stream"); // We understand gzip encoding connection.addRequestProperty("Accept-Encoding", "gzip"); if (cookie != null && cookieHandler != null) { connection.setRequestProperty("Cookie", cookie); } if (cookieHandler == null) { addFromCookieJar(connection); } // Send the request ObjectOutputStream oos = new ObjectOutputStream(connection.getOutputStream()); oos.writeObject(remote.getName()); oos.writeObject(m.getName()); // method name oos.writeObject(m.getParameterTypes()); // formal parameters oos.writeObject(args); // actual parameters oos.flush(); oos.close(); if (cookieHandler == null) { cookieJar.put(new URI(providerURL), connection.getHeaderFields()); } Exception: java.lang.reflect.UndeclaredThrowableException at $Proxy0.updateDocument(Unknown Source) at com.agst.ui.gantt.GanttPanel.doUpdateDocument(GanttPanel.java:1931) at com.agst.ui.gantt.GanttPanel.save(GanttPanel.java:1419) at com.agst.ui.gantt.GanttPanel$4.run(GanttPanel.java:1673) at java.lang.Thread.run(Unknown Source) Caused by: java.net.SocketException: Connection reset at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at sun.net.www.protocol.http.HttpURLConnection$6.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at sun.net.www.protocol.http.HttpURLConnection.getChainedException(Unknown Source) at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source) at com.agst.rmi.RemoteCallHandler.call(RemoteCallHandler.java:196) at com.agst.rmi.RemoteCallHandler.invoke(RemoteCallHandler.java:142) ... 5 more Caused by: java.net.SocketException: Connection reset at java.net.SocketInputStream.read(Unknown Source) at java.io.BufferedInputStream.fill(Unknown Source) at java.io.BufferedInputStream.read1(Unknown Source) at java.io.BufferedInputStream.read(Unknown Source) at sun.net.www.http.HttpClient.parseHTTPHeader(Unknown Source) at sun.net.www.http.HttpClient.parseHTTP(Unknown Source) at sun.net.www.http.HttpClient.parseHTTP(Unknown Source) at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source) at sun.net.www.protocol.http.HttpURLConnection.getHeaderFields(Unknown Source) at com.agst.rmi.RemoteCallHandler.addToCookieJar(RemoteCallHandler.java:529) at com.agst.rmi.RemoteCallHandler.call(RemoteCallHandler.java:192) ... 6 more

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• car and cdr in Scheme are driving me crazy ...

  - by kristian Roger

  Hi Im facing a problem with the car and cdr functions for example: first I defined a list called it x (define x (a (bc) d ( (ef) g ) )) so x now is equal to (a (bc) d ( (ef) g ) ) now for example I need to get the g from this list using only car and cdr (!! noshortcuts as caddr cddr !!) the correct answer is: (car(cdr(car(cdr(cdr(cdr x)))))) BUT how ? :-( I work according to the rules (the car gives the head of list and cdr gives the tail) and instead of getting the answer above I keep reaching wrong answers. Can any one help me in understanding this ... give me step or a way to solve it step by step Thanks in advance. I'm really sick of Scheme.

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• How to make a mutable ItemizedOverlay

  - by Hamy

  Hey all, I would like to make a Google map overlay with changable pins. An easy way to visualize this would be to think of a near real time overlay, where the pins are constantly changing location. However, I can't seem to think of a safe way to do this with the ItemizedOverlay. The problem seems to be the call to populate - If size() is called by some maps thread, and then my data changes, then the result when the maps call accesses getItem() can be an IndexOutOfBoundsException. Can anyone think of a better solution than overloading populate and wrapping super.populate in a synchronized block? Perhaps I could get better luck using a normal Overlay? The Itemized one seems to exist to manage the data for you, perhaps I am making a fundamental mistake by using it? Thanks for any help, my brain is hurting! Hamy

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• WIX: Using a temporary file during install

  - by madbadger

  Hello! I am writing a WIX installer and I have a following requirement: During installation, I need to pass an absolute path to a file (lets call it A) included in my installer to a COM component, which already exists on the hard drive and is a part of another program. I have already written an appropriate Custom Action which expects a path to the file A. I don't want to include A as a file installed in the Program Files folder and removed during the uninstallation process. Instead, I would like to put A only temporary on the hard drive, call my Custom Action which will cause the COM component to use the content of A, and then remove A from disk. Is there an easy way to accomplish this goal? I have tried to utilize the Binary Table and store A there, however I don't know how to reference A using absolute path. I know I could put A outside of MSI file but I would like to keep every file installer needs in a single MSI. Any help would be appreciated.

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• How do I implement something like pointers in javascript?

  - by Shaun

  I know that javascript doesn't have pointers in terms of a variable referring to a place in memory but what I have is a number of variables which are subject to change and dependent on each other. For example: Center (x,y) = (offsetLeft + width/scale , offsetTop + height/scale) As of now I have rewritten the equation in terms of each individual variable and after any changes I call the appropriate update function. For example: If scale changes, then then the center, height, and width stay the same. So I call updateoffset() { offsetLeft = centerx - width/scale; offsetTop = centery - height/scale; } Is this the easiest way to update each of these variables when any of them changes?

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• what is the problem with my javascript code, it is not working.

  - by Shantanu Gupta

  I am trying to call my function named isUrgencyTypeValid from my javascript code but it is not working. Please check what is the problem in my code. My javascript function is not being called. HTML Code <td colspan="2" align="center"><input id="btnSubmit" type="submit" value="submit" runat="server"/></td></tr> jQuery Call function $("#btnSubmit").bind("click",function(){ isUrgencyTypeValid(); }); javascript implemented function function isUrgencyTypeValid() { alert("asd"); var i=0; for(i=0;i<$("radio[name='urgencyType']").length;i++) { if($("radio[name='urgencyType']")[i].checked) { alert($("radio[name='urgencyType']")[i].value); return true; } return false; }

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• Error while exiting cherrypy server

  - by Vijayendra Bapte

  Guys, I am getting following error while exiting cherrypy server. What is this error about? 2009-11-04 09:32:35,015 WARNING Error in atexit._run_exitfuncs: 2009-11-04 09:32:35,015 WARNING 2009-11-04 09:32:35,015 WARNING Traceback (most recent call last): 2009-11-04 09:32:35,015 WARNING File "atexit.pyc", line 24, in _run_exitfuncs 2009-11-04 09:32:35,015 WARNING File "logging\__init__.pyc", line 1486, in shutdown 2009-11-04 09:32:35,015 WARNING File "logging\__init__.pyc", line 746, in flush 2009-11-04 09:32:35,015 WARNING IOError: [Errno 9] Bad file descriptor 2009-11-04 09:32:35,015 WARNING Error in sys.exitfunc: 2009-11-04 09:32:35,015 WARNING Traceback (most recent call last): 2009-11-04 09:32:35,015 WARNING File "atexit.pyc", line 24, in _run_exitfuncs 2009-11-04 09:32:35,015 WARNING File "logging\__init__.pyc", line 1486, in shutdown 2009-11-04 09:32:35,015 WARNING File "logging\__init__.pyc", line 746, in flush 2009-11-04 09:32:35,015 WARNING IOError 2009-11-04 09:32:35,015 WARNING : 2009-11-04 09:32:35,015 WARNING [Errno 9] Bad file descriptor 2009-11-04 09:32:35,015 WARNING

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• Is this an UITableView -beginUpdates documentation error?

  - by mystify

  I can't wrap my head around what they tried to say here in the docs for -beginUpdate: Call this method if you want subsequent insertions, deletion, and selection operations (for example, cellForRowAtIndexPath: and indexPathsForVisibleRows) to be animated simultaneously. Let's see... cellForRowAtIndexPath: and indexPathsForVisibleRows are both GETTER methods. They do not update anything and do not change anything. So why should I call -beginUpdates before calling these? And what's animated regarding these? Well, nothing, huh? Just want to make sure this is really an error in the docs and I didn't miss something.

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• super() in Python 2.x without args

  - by Slava Vishnyakov

  Trying to convert super(B, self).method() into a simple nice bubble() call. Did it, see below! Is it possible to get reference to class B in this example? class A(object): pass class B(A): def test(self): test2() class C(B): pass import inspect def test2(): frame = inspect.currentframe().f_back cls = frame.[?something here?] # cls here should == B (class) c = C() c.test() Basically, C is child of B, B is child of A. Then we create c of type C. Then the call to c.test() actually calls B.test() (via inheritance), which calls to test2(). test2() can get the parent frame frame; code reference to method via frame.f_code; self via frame.f_locals['self']; but type(frame.f_locals['self']) is C (of course), but not B, where method is defined. Any way to get B?

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• Is this casting safe?

  - by Itsik

  I need to write a Util function (in my c++cli app) that converts a String to a Double or Float or Int. template<typename T> static T MyConvert(String^ str) { return static_cast<T>(System::Convert::ToDouble(str)); } Is this safe? Can it somehow convert 2 to 1.999 and then to 1 if I call MyConvert<int>("2") ? I was wondering why the Convert class isn't templated in the first place? (That would let me call Convert<T> instead of Convert.ToDouble() for all types) This is C++/Cli so I can use any convert methods in c++ or .net, but I only know Convert.ToDouble()|ToString()|ToInt32()) Thanks

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• Google app engine error when I login.

  - by zjm1126

  i am using http://code.google.com/p/gaema/source/browse/#hg/demos/webapp, and this is my traceback: Traceback (most recent call last): File "D:\Program Files\Google\google_appengine\google\appengine\ext\webapp\__init__.py", line 510, in __call__ handler.get(*groups) File "D:\gaema\demos\webapp\main.py", line 31, in get google_auth.get_authenticated_user(self._on_auth) File "D:\gaema\demos\webapp\gaema\auth.py", line 641, in get_authenticated_user OpenIdMixin.get_authenticated_user(self, callback) File "D:\gaema\demos\webapp\gaema\auth.py", line 83, in get_authenticated_user url = self._OPENID_ENDPOINT + "?" + urllib.urlencode(args) File "D:\Python25\lib\urllib.py", line 1250, in urlencode v = quote_plus(str(v)) UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-1: ordinal not in range(128) how to do this thanks updated i change the code from args = dict((k, v[-1]) for k, v in self.request.arguments.iteritems()) args["openid.mode"] = u"check_authentication" url = self._OPENID_ENDPOINT + "?" + urllib.urlencode(args) to args = dict((k, v[-1].encode('utf-8')) for k, v in self.request.arguments.iteritems()) args["openid.mode"] = u"check_authentication" url = self._OPENID_ENDPOINT + "?" + urllib.urlencode(args) but also error.

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• Using jep.invoke() method

  - by hofsoc

  Hi, I need to call a function from a python script and pass in parameters into it. I have a test python script which I can call and run from java using Jepp - this then adds the person. Eg Test.py import Finding from Finding import * f = Finding() f.addFinding("John", "Doe", 27) Within my Finding class I have addFinding(firstname, lastName, age) However, I wish to be able to do this from within java. Should I be using the jep.invoke() method. Does anyone have a hello world example of such a thing being done or forward me to some good examples? Does anyone have any suggestions please? Thanks in advance

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• Calling Graphviz dot from Java

  - by garsh0p

  What's the best way to call an external program (graphviz's dot in this case) from a Java program and grab the output?

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• Best way to get an Application Context into a static method in Android

  - by Slapout

  I'm working on an Android application that has several Activities. In it I have a class with several static methods. I would like to be able to call these methods from the different Activities. I'm using the static methods to load data from an xml file via a XmlResourceParser. To create a XmlResourceParser requires a call on the Application Context. So my question is, what is the best way to get a reference to the Application Context into the static methods? Have each Activity get it and pass it in? Store it somehow in a global variable?

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• Usage CursorLoader without ContentProvider

  - by sealskej

  Android SDK documentation says that startManagingCursor() method is depracated: This method is deprecated. Use the new CursorLoader class with LoaderManager instead; this is also available on older platforms through the Android compatibility package. This method allows the activity to take care of managing the given Cursor's lifecycle for you based on the activity's lifecycle. That is, when the activity is stopped it will automatically call deactivate() on the given Cursor, and when it is later restarted it will call requery() for you. When the activity is destroyed, all managed Cursors will be closed automatically. If you are targeting HONEYCOMB or later, consider instead using LoaderManager instead, available via getLoaderManager() So I would like to use CursorLoader. But how can I use it with custom CursorAdapter and without ContentProvider, when I needs URI in constructor of CursorLoader?

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• Linking to a C library compiled as C++

  - by Jacob

  I'm in linker paradise now. I have a C library which only compiles in Visual C++ (it probably works in gcc) if: I compile it as C++ code Define __cplusplus which results in all the declarations being enclosed in extern "C" { } So, by doing this I have a static library called, say, bsbs.lib Now, I have a C++ project called Tester which would like to call function barbar in declared in bsbs.h. All goes fine, until I try to link to bsbs.lib where I get the all-too-familiar: Tester.obj : error LNK2001: unresolved external symbol _foofoo And it always seems to be foofoo which cannot be resolved regardless of which function I call in Tester (barbar or anything else).

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• Dojo slider: update value dynamically

  - by xApple

  I am building an application where the user browses certain objects by scrolling and zooming. To change the zoom level I have successfully implemented a "dijit.form.HorizontalSlider" object. Every time the user changes the position of the silder, I can catch the "onChange" call and do something with that. However, the user can also zoom-in by double clicking inside the view zone, at which point the slider should change position automatically to reflect the new zoom level. My question is the following: what function or method should I call in my javascript to update the position of a dojo silder ? Here is the code that creates the silder object: var zoomSlider = new dijit.form.HorizontalSlider({ name: "zoom_slider", id: "zoom_slider", value: 0, minimum: 0, maximum: 19, discreteValues: 20, intermediateChanges: false, style: "width: 160px;", onChange: function(value) { brwsr.view.zoomTo(value); } }, "zoom_slider"); navbox_silder.appendChild(zoomSlider.domNode);

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• How does dereferencing of a function pointer happen?

  - by eSKay

  Why and how does dereferencing a function pointer just "do nothing"? This is what I am talking about: #include<stdio.h> void hello() { printf("hello"); } int main(void) { (*****hello)(); } From a comment over here: function pointers dereference just fine, but the resulting function designator will be immediately converted back to a function pointer And from an answer here: Dereferencing (in way you think) a function's pointer means: accessing a CODE memory as it would be a DATA memory. Function pointer isn't suppose to be dereferenced in that way. Instead, it is called. I would use a name "dereference" side by side with "call". It's OK. Anyway: C is designed in such a way that both function name identifier as well as variable holding function's pointer mean the same: address to CODE memory. And it allows to jump to that memory by using call () syntax either on an identifier or variable. How exactly does dereferencing of a function pointer work?

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• Luasql and SQLite?

  - by OverTheRainbow

  Hello I just got started looking at Lua as an easy way to access the SQLite DLL, but I ran into an error while trying to use the DB-agnostic LuaSQL module: require "luasql.sqlite" module "luasql.sqlite" print("Content-type: Text/html\n") print("Hello!") Note that I'm trying to start from the most basic setup, so only have the following files in the work directory, and sqlite.dll is actually the renamed sqlite3.dll from the LuaForge site: Directory of C:\Temp <DIR> luasql lua5.1.exe lua5.1.dll hello.lua Directory of C:\Temp\luasql sqlite.dll Am I missing some binaries that would explain the error? Thank you. Edit: I renamed the DLL to its original sqlite3.dll and updated the source to reflect this (originally renamed it because that's how it was called in a sample I found). At this point, here's what the code looks like... require "luasql.sqlite3" -- attempt to call field 'sqlite' (a nil value) env = luasql.sqlite() env:close() ... and the error message I'm getting: C:\>lua5.1.exe hello.lua lua5.1.exe: hello.lua:4: attempt to call field 'sqlite' (a nil value)

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• Stopping httpd causes a process started from perl CGI script to receive SIGTERM

  - by Pranav Pal

  I am running a shell script from a perl CGI script: #!/usr/bin/perl my $command = "./script.sh &"; my $pid = fork(); if (defined($pid) && $pid==0) { # background process system( $command ); } The shell script looks like this: #!/bin/sh trap 'echo trapped' 15 tail -f test.log When I run the CGI script from browser, and then stop httpd using /etc/init.d/httpd stop, the script receives a SIGTERM signal. I was expecting the script to run as a separate process and not be tied in anyway to httpd. Though I can trap the SIGTERM, I would like to understand why the script is receiving SIGTERM at all. What wrong am I doing here? I am running RHEL 5.8 and Apache HTTP server 2.4. Thanks, Pranav

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• user notification while waiting

  - by user315445

  I am writing a simple win forms app in C#. There is a method call in my method which loads files but is taking a while to respond. Below is the method call Directory.GetFiles(selectedFolder, "*.xml", SearchOption.AllDirectories); I want to notify this to users. Is there a way to show them that file loading is in progress? I want a simplest way. I suppose Splash screen is too costly for my app.

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