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• How does an interpreter switch scope?

  - by Dox

  I'm asking this because I'm relatively new to interpreter development and I wanted to know some basic concepts before reinventing the wheel. I thought of the values of all variables stored in an array which makes the current scope, upon entering a function the array is swapped and the original array put on some sort of stack. When leaving the function the top element of the "scope stack" is popped of and used again. Is this basically right? Isn't swapping arrays (which means moving around a lot of data) not very slow and therefore not used by modern interpreters?

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• execute java class with ant

  - by cateof

  I want my ant script to execute the command java -cp libs/a.jar:libs/b.jar org.stack.class1 --package pName --out classes new.wsdl How can I do it with an Ant script? The following does not work <?xml version="1.0" encoding="UTF-8"?> project name="class" default="compile"> <target name="compile"> <java classname="org.stack.class1" fork="true"> <classpath> <pathelement location="libs/a.jar"/> <pathelement location="libs/b.jar"/> </classpath> <arg value="--package pName --out classes new.wsdl"/> </java> </target>

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• Practicing buffer overflow attack in Ubuntu

  - by wakandan

  I am trying to learn to use buffer overflow attack in Ubuntu. Unfortunately, I cannot turn off Address Space Layout Randomization (ASLR) feature in this OS, which is turned on by default. I have tried some work around found in some fedora books: echo "0" > /proc/sys/kernel/randomize_va_space but for some reason the protection's still there. Please give me some suggestions. Thanks. [edit]Actually the above command was not successful, it said "Permission Denied", even with sudo. How can I fix that? [adding] I kept on getting segmetation fault error when it shows an address in stack. Is it related to non-executable stack in ubuntu :(?

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• Bitmap Crashing upon going back and re-entering Activity

  - by dagonal

  Hello, I'm not sure what is causing this...I have two Activities, first has a button that goes to the second. The second creates a Bitmap object, assigns it a picture from the sdcard and loads it into an ImageView. Problem is when I go into the second Activity, then press the back button, and then go back into the second Activity, it crashes. I have no clue why. I did an extensive google search but to no avail. I can post the source code if you want. Please let me know. Thanks in advance! I got this from the LogCat: "E/dalvikvm( 4869): Unable to open stack trace file '/data/anr/traces.txt': Permission denied" I'm not sure how to get the stack trace.

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• Sockets: RAW or STREAM

  - by user1415536

  May be the question is a bit stupid, but I'll ask it. I read a lot about raw sockets in network, have seen several examples. So, basically with raw sockets it's possible to build own stack of headers, like stack = IP + TCP/UDP + OWN_HEADER. My question is, is it possible to get some kind of ready frame of first two(IP + TCP/UDP) from the linux kernel and then just append own header to them? The operating system in question is linux and the language is C. I cannot find any function which can do such a thing, but may be I'm digging in a wrong direction.

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• The implicit function __strcpy_chk() call

  - by Summer_More_More_Tea

  Hi everyone: I'm now performing a stack buffer overflow attack test on my own PC( Ubuntu 9.10, gcc-4.4.1 ) based on the article http://www.tenouk.com/Bufferoverflowc/Bufferoverflow4.html. Yet I haven't achieved the goal. Each time a segfault is thrown accompanied with some error informaiton. I compile the source code, and wanna get further information using objdump. Function __strcpy_chk is invoked in the assembly code dumped out, and it's said that "The __strcpy_chk() function is not in the source standard; it is only in the binary standard." Does this the mechanism a compiler employed to protect runtime stack? To finish my test, how can I bypass the protection? Regards.

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• Asp.net - Invalid postback or callback argument. Event validation is enabled using '<pages enableEv

  - by Jangwenyi

  I am getting the following error when I post back a page from the client-side. I have javascript code that modifies an asp:listbox on the client side. How do we fix this? Error details below: Server Error in '/XXX' Application. -------------------------------------------------------------------------------- Invalid postback or callback argument. Event validation is enabled using <pages enableEventValidation="true"/> in configuration or <%@ Page EnableEventValidation="true" %> in a page. For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them. If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.ArgumentException: Invalid postback or callback argument. Event validation is enabled using <pages enableEventValidation="true"/> in configuration or <%@ Page EnableEventValidation="true" %> in a page. For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them. If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation. Source Error: An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. Stack Trace: [ArgumentException: Invalid postback or callback argument. Event validation is enabled using <pages enableEventValidation="true"/> in configuration or <%@ Page EnableEventValidation="true" %> in a page. For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them. If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation.] System.Web.UI.ClientScriptManager.ValidateEvent(String uniqueId, String argument) +2132728 System.Web.UI.Control.ValidateEvent(String uniqueID, String eventArgument) +108 System.Web.UI.WebControls.ListBox.LoadPostData(String postDataKey, NameValueCollection postCollection) +274 System.Web.UI.WebControls.ListBox.System.Web.UI.IPostBackDataHandler.LoadPostData(String postDataKey, NameValueCollection postCollection) +11 System.Web.UI.Page.ProcessPostData(NameValueCollection postData, Boolean fBeforeLoad) +353 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1194 -------------------------------------------------------------------------------- Version Information: Microsoft .NET Framework Version:2.0.50727.1433; ASP.NET Version:2.0.50727.1433

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• need for tcp fine-tuning on heavily used proxy server

  - by Vijay Gharge

  Hi all, I am using squid like Internet proxy server on RHEL 4 update 6 & 8 with quite heavy load i.e. 8k established connections during peak hour. Without depending much on application provider's expertise I want to achieve maximum o/p from linux. W.r.t. that I have certain questions as following: How to find out if there is scope for further tcp fine-tuning (without exhausting available resources) as the benchmark values given by vendor looks poor! Is there any parameter value that is available from OS / network stack that will show me the results. If at all there is scope, how shall I identify & configure OS tcp stack parameters i.e. using sysctl or any specific parameter Post tuning how shall I clearly measure performance enhancement / degradation ?

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• iPhone development forum recommendations

  - by iphonedeveloper

  What good iPhone development forums do you recommend? (beyond Stack Overflow..)

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• Basic data alignment question

  - by Broken Logic

  I've been playing around to see how my computer works under the hood. What I'm interested in is seeing is what happens on the stack inside a function. To do this I've written the following toy program: #include <stdio.h> void __cdecl Test1(char a, unsigned long long b, char c) { char c1; unsigned long long b1; char a1; c1 = 'b'; b1 = 4; a1 = 'r'; printf("%d %d - %d - %d %d Total: %d\n", (long)&b1 - (long)&a1, (long)&c1 - (long)&b1, (long)&a - (long)&c1, (long)&b - (long)&a, (long)&c - (long)&b, (long)&c - (long)&a1 ); }; struct TestStruct { char a; unsigned long long b; char c; }; void __cdecl Test2(char a, unsigned long long b, char c) { TestStruct locals; locals.a = 'b'; locals.b = 4; locals.c = 'r'; printf("%d %d - %d - %d %d Total: %d\n", (long)&locals.b - (long)&locals.a, (long)&locals.c - (long)&locals.b, (long)&a - (long)&locals.c, (long)&b - (long)&a, (long)&c - (long)&b, (long)&c - (long)&locals.a ); }; int main() { Test1('f', 0, 'o'); Test2('f', 0, 'o'); return 0; } And this spits out the following: 9 19 - 13 - 4 8 Total: 53 8 8 - 24 - 4 8 Total: 52 The function args are well behaved but as the calling convention is specified, I'd expect this. But the local variables are a bit wonky. My question is, why wouldn't these be the same? The second call seems to produce a more compact and better aligned stack. Looking at the ASM is unenlightening (at least to me), as the variable addresses are still aliased there. So I guess this is really a question about the assembler itself allocates the stack to local variables. I realise that any specific answer is likely to be platform specific. I'm more interested in a general explanation unless this quirk really is platform specific. For the record though, I'm compiling with VS2010 on a 64bit Intel machine.

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• What does ESP mean in assembly?

  - by Mask

  ESP = ? stack pointer What does E stand for here?

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• win7 + vc7.1 + mfc = stackoverflow

  - by fogbit

  Hello! I've moved my vc7.1 project from WInXP to Win7. After rebuilding i got stackoverflow error in function _malloc_dbg when i start the program. "Unhandled exception at 0x0051bf0f in XXX.exe: 0xC00000FD: Stack overflow." Call stack: msvcr71d.dll!_malloc_dbg(unsigned int nSize=140, int nBlockUse=2, const char * szFileName=0x10267784, int nLine=163) msvcr71d.dll!_calloc_dbg(unsigned int nNum=1, unsigned int nSize=140, int nBlockUse=2, const char * szFileName=0x10267784, int nLine=163) msvcr71d.dll!_mtinit() msvcr71d.dll!_CRTDLL_INIT(void * hDllHandle=0x10200000, unsigned long dwReason=1, void * lpreserved=0x0018fd24) I tried to set up different stacksizes in project options (from 10 to 100 mbytes), in all cases i got this error. How can i fix this?

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• To "null" or not to "null" my class's attributes

  - by Helper Method

  When I write a class in Java, I like to initialize the attributes which are set to a default value directly and attributes which are set by the caller in the constructor, something like this: public class Stack<E> { private List<E> list; private size = 0; public Stack(int initialCapacity) { list = new ArrayList<E>(initialCapacity); } // remainder omitted } Now suppose I have a Tree class: public class Tree<E> { private Node<E> root = null; // no constructor needed, remainder omitted } Shall I set the root attribute to null, to mark that it is set to null by default, or omit the null value?

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• .NET Performance: Deep Recursion vs Queue

  - by JeffN825

  I'm writing a component that needs to walk large object graphs, sometimes 20-30 levels deep. What is the most performant way of walking the graph? A. Enqueueing "steps" so as to avoid deep recursion or B. A DFS (depth first search) which may step many levels deep and have a "deep" stack trace at times. I guess the question I'm asking is: Is there a performance hit in .NET for doing a DFS that causes a "deep" stack trace? If so, what is the hit? And would I better better off with some BFS by means of queueing up steps that would have been handled recursively in a DFS? Sorry if I'm being unclear. Thanks.

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• Rails streaming file download

  - by Leonard Teo

  I'm trying to implement a file download with Rails. I want to eventually migrate this code to using S3 to serve the file. I've copied the Rails send_file code almost verbatim and I cannot seem to get it to stream a file to the user. What happens is that it sends 'a' file to the user, but the downloaded file itself simply contains the text.inspect of the Proc: # What am I doing wrong here? options = {} options[:length] = File.size(file.path) options[:filename] = File.basename(file.path) send_file_headers! options render :status => 200, :text => Proc.new { |response, output| len = 4096 File.open(file.path, 'rb') do |fh| while buf = fh.read(len) output.write(buf) end end } Ps: I've read in a number of other posts that it's not advisable to send files through the Rails stack, and if possible serve using the web server, or in the case of S3 use the hashed URL it can provide. Yes, we really do want to serve the file through the Rails stack.

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• Polymorphic classes in templates

  - by soxarered

  Let's say we have a class hierarchy where we have a generic Animal class, which has several classes directly inherit from it (such as Dog, Cat, Horse, etc..). When using templates on this inheritance hierarchy, is it legal to just use SomeTemplateClass<Animal> and then shove in Dogs and Cats and Horses into this templated object? For example, assume we have a templated Stack class, where we want to host all sorts of animals. Can I simply state Stack<Animal> s; Dog d; s.push(d); Cat c; s.push(c);

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• Open source framework à la Microsoft Sync Framework suggestions?

  - by drskol

  We are implementing a warehouse management system atop an open source stack (Java, web services & friends). In this system, we want to integrate many mobile devices which should also be capable of adequate online/offline functionality, e.g. preparing database inserts while a mobile device is temporarily unconnected, and performing them on the backend database when reconnected. For a .NET stack, Microsoft Sync Framework would be a perfect solution, e.g. to do database replication and hoarding. Can anyone suggest an open source alternative to the MS Sync Framework and possibly describe his experiences with it? Thanks in advance for any answers.

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• How do I set properties related to the calling method's scope?

  - by Thiado de Arruda

  I'm not looking for a way to associate values with a thread using the 'SetData' method. I need to store some kind of data that will only exist during the scope of a calling method, could be the immediate parent or any other call that is made down on the stack. For example: void SomeMethod() { string someInfo = "someInfo"; SomeOtherMethod(); object data = GetDataOnCurrentScope("someKey"); } void SomeOtherMethod() { SetDataOnParentScope("someKey", somevalue); } In this case both the 'someInfo' local variable and the data set with the "someKey" key will disapear after 'SomeMethod' returns. Is something like this possible? This may go against the rules of a stack, but who knows if someone has an idea...

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• error: expected `;' before '{' token - What is the cause?

  - by melee

  Here is my implementation file: using namespace std; #include <iostream> #include <iomanip> #include <string> #include <stack> //line 5 #include "proj05.canvas.h" //----------------Constructor----------------// Canvas::Canvas() //line 10 { Title = ""; Nrow = 0; Ncol = 0; image[][100]; // line 15 position.r = 0; position.c = 0; } //-------------------Paint------------------// line 20 void Canvas::Paint(int R, int C, char Color) { cout << "Paint to be implemented" << endl; } The errors I'm getting are these: proj05.canvas.cpp: In function 'std::istream& operator>>(std::istream&, Canvas&)': proj05.canvas.cpp:11: error: expected `;' before '{' token proj05.canvas.cpp:22: error: a function-definition is not allowed here before '{' token proj05.canvas.cpp:24: error: expected `}' at end of input proj05.canvas.cpp:24: error: expected `}' at end of input These seem like simple syntax errors, but I am not sure what's wrong. Could someone decode these for me? I'd really appreciate it, thanks for your time! EDIT Here is the definition of Canvas in my .h file: #ifndef CANVAS_H #define CANVAS_H #include <iostream> #include <iomanip> #include <string> #include <stack> class Canvas { public: Canvas(); void Paint(int R, int C, char Color); const int Nrow; const int Ncol; string Title; int image[][100]; stack<int> path; struct PixelCoordinates { unsigned int r; unsigned int c; } position; }; #endif

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• Emulate back button in multi-view TabActivity

  - by ZelluX

  Hi, all I have a TabActivity with several tabs. Each tab corresponds to a specific view, and those views may further switch to other views. For example, one of my tabs displays RSS feed list, after user clicks one of the RSS feed, it will switch to a view displaying a list of articles, and after user clicks one of the titles, a full article view will be displayed. I'm going to add support for "back" button in my application. For instance, in a full article view, after user presses the "back" button, it should switch back to the article list view. And if user presses it the "back" button again, my application should switch back to the feed list view. My idea is to maintain a Stack<View> during navigation, and every time user presses the "back" button, the program will pop a View out of the stack, and set it as the current view. But I would like to know how to set current view in TabHost. Many thanks.

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• Postfix and right-associative operators in LR(0) parsers

  - by Ian

  Is it possible to construct an LR(0) parser that could parse a language with both prefix and postfix operators? For example, if I had a grammar with the + (addition) and ! (factorial) operators with the usual precedence then 1+3! should be 1 + 3! = 1 + 6 = 7, but surely if the parser were LR(0) then when it had 1+3 on the stack it would reduce rather than shift? Also, do right associative operators pose a problem? For example, 2^3^4 should be 2^(3^4) but again, when the parser have 2^3 on the stack how would it know to reduce or shift? If this isn't possible is there still a way to use an LR(0) parser, possibly by converting the input into Polish or Reverse Polish notation or adding brackets in the appropriate places? Would this be done before, during or after the lexing stage?

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• How to remove the shadow from a librarystack

  - by red-X

  I'm currently in a project where I need a LibraryStack with no visuals at all, so it would just show the content. If I just remove the background a shadow stays in view which I cant seem to remove... This code looks like: <s:LibraryStack Background="Transparent"> <s:LibraryStackItem Background="AliceBlue"/> <s:LibraryStackItem Background="Bisque"/> <s:LibraryStackItem Background="Salmon"/> </s:LibraryStack> This stack is just for explaining purposes, the actual stack is added in the code behind in c#. So preferably any answers that would be usefull to add in c#.

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• Implementation communication protocols in C/C++

  - by MeThinks

  I am in the process of starting to implement some proprietary communication protocol stack in software but not sure where to start. It is the kind of work I have not done before and I am looking for help in terms of resources for best/recommended approaches. I will be using c/c++ and I am free to use use libraries (BSD/BOOST/Apache) but no GPL. I have used C++ extensively so using the features of C++ is not a problem. The protocol stack has three layers and it is already fully specified and formally verified. So all I need to do is implemented and test it fully in the specified languages. Should also mention that protocol is very simple but can run on different devices over a reliable physical transport layer Any help with references/recommendations will be appreciated. I am willing to use a different language if only to help me understand how to implement them but I will have to eventually resort to the language of choice.

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• std::string vs. char*

  - by Elofin

  does std::string store data differently than a char* on either stack or heap or is it just derived from char* into a class?

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• Application crashes when popViewControllerAnimated is called while scrolling

  - by Aldrich

  In one screen I have a custom toolbar with a "close" button in it, and a UIScrollView. In the screen that preceded this one I had pushed the current screen into the navigation stack. I had also disabled the navigation toolbar for a larger display area and so the close button would instead be used to call: - (void)doClose { [self.navigationController popViewControllerAnimated:YES]; } Now here's the problem: the application crashes when the close button is pressed, while the UIScrollView is moving. Here's the debugger stack trace: 0 __forwarding__ 1 __forwarding_prep_0___ 2 -[UIToolbarButton setHighlighted:] 3 -[UIControl(Static) _unhighlight] 4 __NSFireDelayedPerform ... and I do have the following line in the debugger console: *** -[CALayer setOpacity:]: message sent to deallocated instance 0x718d250 (sometimes setOpacity would be setNeedsDisplay or something related) There won't be any crashes while the scrollview is at rest. What is happening?

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