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  • C++ Return by reference

    - by Gokul
    Say, i have a function which returns a reference and i want to make sure that the caller only gets it as a reference and should not receive it as a copy. Is this possible in C++? Thanks, Gokul.

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  • undefined reference errors in C++

    - by Phenom
    I have files Record.h and Record.cpp. When I just include the Record.h file, I get several undefined reference errors to functions defined in those files. When I also include Record.cpp then the errors go away. Why is that? Record.h has the forward declarations for the functions it says are an undefined reference.

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  • How to include the right reference in C# using the "Browser" tab

    - by vizcaynot
    Hello: I am working on VS2010 C# and I want to add a .dll reference compiled under VS2008; this .dll exists in 2 versions: Debug and Release. The .dll is not under .NET, COM or projects tabs, so I only have the "browser" tab to add the .dll to the reference. My question is: How can I indicate to VS to take the release .dll version when I compile in the release mode and to take the debug .dll version when I compile in the debug mode? Thanks.

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  • reference function from another function

    - by JohnWong
    I forgot how to reference another function into a function in C++? In python it is declare as a class so that I can use it. double footInches(double foot) { double inches = (1.0/12.00) * foot; return inches; } double inchMeter(double inch) { double meter = 39.37 * (footInches(inches)); return meter; } I want to reference footInches in inchMeter.

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  • C++ Why isn't call by reference needed for strcpy()

    - by Ribbs
    I have a homework assignment with a number of questions. One is asking why the strcpy() function doesn't need the call by reference operator for CStrings. I've looked through the book numerous times and I can't, for the life of me, find the answer. Can anyone help explain this to me? It is an array of sorts so I would think you would need the call by reference.

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  • Java reference storage question

    - by aab
    In java, when you pass an object to a method as a parameter, it is actually passing a reference, or a pointer, to that object because objects in Java are references. Inside the function, it has a pointer to that object which is a location in memory. I am wondering where this pointer lives in memory? Is a new memory location created once inside the function to hold this reference?

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  • System Expandable-String Environment Variables Can’t Reference User Environment Variables

    - by Synetech inc.
    Hi, I’ve run into a bit of a situation with Windows environment variables. I’ve narrowed it down to what may or may not makes sense and/or possibly be by design. It seems that expandable-string environment variables of the local machine cannot reference environment variables of the current user. For example if you’ve got the following environment variables: [HKCU\Environment] "CU"="CU" "CU->LM"="%LM%" [HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Environment] "LM"="LM" "LM->CU"="%CU%" Then you get the following results: > set CU CU=CU CU->LM=LM > set LM LM=LM LM->CU=%CU% It seems that user variables can expand system variable references, but system variables cannot expand (access?) user variable references. I suppose that it makes sense if you think about it just right (eg like how user vars override/hide system vars of the same name), but it also doesn’t make sense if you think about it in even more ways. So what’s going on? Is there a way to get this to work as expected? Thanks.

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  • gcc built by crosstool-ng gives undefined reference

    - by netvope
    I've successfully built a toolchain using crosstool-ng with the default configuration named x86_64-unknown-linux-gnu. The documentation says: Using the toolchain is as simple as adding the toolchain's bin directory in your PATH, such as: export PATH="${PATH}:/your/toolchain/path/bin" and then using the target tuple to tell the build systems to use your toolchain: ./configure --target=your-target-tuple or make CC=your-target-tuple-gcc or make CROSS_COMPILE=your-target-tuple- and so on... I followed the instructions and attempted to build GNU tar (tar-1.25.tar.bz2) with the toolchain. The commands ./configure --target=x86_64-unknown-linux-gnu and make CROSS_COMPILE=x86_64-unknown-linux-gnu- do not work (the build will succeed, but it uses the host system's gcc). The command make CC=x86_64-unknown-linux-gnu-gcc works, but in the very last step when it tries to link, it returns errors like this: compare.o: In function `openat': /dev/shm/x-tools/x86_64-unknown-linux-gnu/x86_64-unknown-linux-gnu/sys-root/usr/include/bits/fcntl2.h:134: undefined reference to `__openat_2' What could be the problem? Was the toolchain not properly setup? Perhaps x86_64-unknown-linux-gnu-gcc is using the header files from the host system but could not find the libraries in the target's sys-root?

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  • Reference entire excel 2007 sheet to another sheet

    - by Keikoku
    I have one sheet with 100 rows of data. I have a second sheet that will use the same data but with filters applied. In fact, I will have a dozen sheets, each with different filters. My goal is to have references from the every sheet to the first so that prior to filtering, they all contain exactly the same data. This way I only have to modify one sheet and all sheets will reflect the changes. The purpose is to create external links from word to excel to display specific rows, but there appears to be a limitation to linking where it displays absolutely everything that you see on the sheet itself (and each view must be different). I can manually reference the first cell and then drag the black box to easily expand it to the required number of rows, but that would require me to go into each sheet and drag the black box again whenever I add new entries to the master copy. Is there an easy way to do this? Note that the issue is the same as Easy way for users to update linked documents Excel 2007, except this time I am using a different approach. Solutions to both would be welcome.

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  • Can I implement the readers and writers algorithm in OpenMP by replacing counting semaphores with another feature?

    - by DeveloperDon
    After reading about OpenMP and not finding functions to support semaphores, I did an internet search for OpenMP and the readers and writers problem, but found no suitable matches. Is there a general method for replacing counting semaphores in OpenMP with something that it supports? Or is there just a gap in the environment where it does not permit things that are asymmetrical like the third readers and writers problem shown on the following page? http://en.wikipedia.org/wiki/Readers-writers_problem#The_third_readers-writers_problem

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  • Can you force a crash if a write occurs to a given memory location with finer than page granularity?

    - by Joseph Garvin
    I'm writing a program that for performance reasons uses shared memory (alternatives have been evaluated, and they are not fast enough for my task, so suggestions to not use it will be downvoted). In the shared memory region I am writing many structs of a fixed size. There is one program responsible for writing the structs into shared memory, and many clients that read from it. However, there is one member of each struct that clients need to write to (a reference count, which they will update atomically). All of the other members should be read only to the clients. Because clients need to change that one member, they can't map the shared memory region as read only. But they shouldn't be tinkering with the other members either, and since these programs are written in C++, memory corruption is possible. Ideally, it should be as difficult as possible for one client to crash another. I'm only worried about buggy clients, not malicious ones, so imperfect solutions are allowed. I can try to stop clients from overwriting by declaring the members in the header they use as const, but that won't prevent memory corruption (buffer overflows, bad casts, etc.) from overwriting. I can insert canaries, but then I have to constantly pay the cost of checking them. Instead of storing the reference count member directly, I could store a pointer to the actual data in a separate mapped write only page, while keeping the structs in read only mapped pages. This will work, the OS will force my application to crash if I try to write to the pointed to data, but indirect storage can be undesirable when trying to write lock free algorithms, because needing to follow another level of indirection can change whether something can be done atomically. Is there any way to mark smaller areas of memory such that writing them will cause your app to blow up? Some platforms have hardware watchpoints, and maybe I could activate one of those with inline assembly, but I'd be limited to only 4 at a time on 32-bit x86 and each one could only cover part of the struct because they're limited to 4 bytes. It'd also make my program painful to debug ;)

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  • Postfix flow/hook reference, or high-level overview?

    - by threecheeseopera
    The Postfix MTA consists of several components/services that work together to perform the different stages of delivery and receipt of mail; these include the smtp daemon, the pickup and cleanup processes, the queue manager, the smtp service, pipe/spawn/virtual/rewrite ... and others (including the possibility of custom components). Postfix also provides several types of hooks that allow it to integrate with external software, such as policy servers, filters, bounce handlers, loggers, and authentication mechanisms; these hooks can be connected to different components/stages of the delivery process, and can communicate via (at least) IPC, network, database, several types of flat files, or a predefined protocol (e.g. milter). An old and very limited example of this is shown at this page. My question: Does anyone have access to a resource that describes these hooks, the components/delivery stages that the hook can interact with, and the supported communication methods? Or, more likely, documentation of the various Postfix components and the hooks/methods that they support? For example: Given the requirement "if the recipient primary MX server matches 'shadysmtpd', check the recipient address against a list; if there is a match, terminate the SMTP connection without notice". My software would need to 1) integrate into the proper part of the SMTP process, 2) use some method to perform the address check (TCP map server? regular expressions? mysql?), and 3) implement the required action (connection termination). Additionally, there will probably be several methods to accomplish this, and another requirement would be to find that which best fits (ex: a network server might be faster than a flat-file lookup; or, if a large volume of mail might be affected by this check, it should be performed as early in the mail process as possible). Real-world example: The apolicy policy server (performs checks on addresses according to user-defined rules) is designed as a standalone TCP server that hooks into Postfix inside the smtpd component via the directive 'check_policy_service inet:127.0.0.1:10001' in the 'smtpd_client_restrictions' configuration option. This means that, when Postfix first receives an item of mail to be delivered, it will create a TCP connection to the policy server address:port for the purpose of determining if the client is allowed to send mail from this server (in addition to whatever other restrictions / restriction lookup methods are defined in that option); the proper action will be taken based on the server's response. Notes: 1)The Postfix architecture page describes some of this information in ascii art; what I am hoping for is distilled, condensed, reference material. 2) Please correct me if I am wrong on any level; there is a mountain of material, and I am just one man ;) Thanks!

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  • Reference for proper handling of PID file on Unix

    - by bignose
    Where can I find a well-respected reference that details the proper handling of PID files on Unix? On Unix operating systems, it is common practice to “lock” a program (often a daemon) by use of a special lock file: the PID file. This is a file in a predictable location, often ‘/var/run/foo.pid’. The program is supposed to check when it starts up whether the PID file exists and, if the file does exist, exit with an error. So it's a kind of advisory, collaborative locking mechanism. The file contains a single line of text, being the numeric process ID (hence the name “PID file”) of the process that currently holds the lock; this allows an easy way to automate sending a signal to the process that holds the lock. What I can't find is a good reference on expected or “best practice” behaviour for handling PID files. There are various nuances: how to actually lock the file (don't bother? use the kernel? what about platform incompatibilities?), handling stale locks (silently delete them? when to check?), when exactly to acquire and release the lock, and so forth. Where can I find a respected, most-authoritative reference (ideally on the level of W. Richard Stevens) for this small topic?

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  • Requiring library consumers reference additional assembly when using certain types

    - by Thomas G. Mayfield
    I have library code that uses ICSharpCode.SharpZipLib under the hood to make it easy to use ZIP files as data sources when running integration tests. As it stands, if I reference my library from another project, the other project will compile just fine, but when it accesses the code that uses SharpZipLib, I get an exception for it not finding the zip library: failed: System.IO.FileNotFoundException : Could not load file or assembly 'ICSharpCode.SharpZipLib, Version=0.85.5.452, Culture=neutral, PublicKeyToken=1b03e6acf1164f73' or one of its dependencies. The system cannot find the file specified. If the types in my library derived from a class in SharpZipLib, it'd generate a compile error CS0012. What other ways are there for triggering a CS0012, so that using code that requires SharpZipLib (but doesn't clearly indicate it) would cause consumer code to fail compilation? I've had similar problems in the past when I've used libraries like DeftTech.DuckTyping under the hood. I'd add my library code to a new project, start working, compile, run, and then suddenly hit an edge case that I'd used duck typing to get around and get a runtime error. What I'd most like is to have the same behavior as if I'd derived from a type in the 3rd-party library, so that a reference to my derived type generates a CS0012: The type 'type' is defined in an assembly that is not referenced. You must add a reference to assembly 'assembly'.

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  • mysql prevent displaying a row ONE which has reference in another row TWO but no reference in row THREE

    - by Jayapal Chandran
    I have a table like the following id | name | pid 1 | sam | NULL 2 | sams ref | 1 3 | pam | NULL For the first time the first row gets inserted which will have pid as null I insert a row which is related to the first row and then i insert a row which is new and which may be referred by another row in future. now i want only the third row to be displayed and not the first and second row as the second row contains the reference of first row. so if any row has a reference to another row then both the rows should not be displayed. Only rows which is not having any reference should be displayed. BESIDES, IS IT A GOOD PRACTICE? PLEASE ADVICE ON THIS. Edited When i updated in server the query is always giving empty result. here is what i have and this one When pid is NULL then that row should appear but when another entry in the same table with pid as its parent id or any other rows id appears then both the rows should not appear. so if any pid has been referred then both the rows should not appear. here only one row will refer another row and not more than that. in my localhost i have mysql version 5.0.1 or something like that but when i installed xampp in another system it had 5.5 and in the live server it was 5.3 so in version around 5.0 the query is returning rows but in higher versions it is returning empty rows. so now i this case how to make a query?

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  • Javascript: "Dangling" Reference to DOM element?

    - by Channel72
    It seems that in Javascript, if you have a reference to some DOM element, and then modify the DOM by adding additional elements to document.body, your DOM reference becomes invalidated. Consider the following code: <html> <head> <script type = "text/javascript"> function work() { var foo = document.getElementById("foo"); alert(foo == document.getElementById("foo")); document.body.innerHTML += "<div>blah blah</div>"; alert(foo == document.getElementById("foo")); } </script> </head> <body> <div id = "foo" onclick='work()'>Foo</div> </body> </html> When you click on the DIV, this alerts "true", and then "false." So in other words, after modifying document.body, the reference to the DIV element is no longer valid. This behavior is the same on Firefox and MSIE. Some questions: Why does this occur? Is this behavior specified by the ECMAScript standard, or is this a browser-specific issue? Note: there's another question posted on stackoverflow that seems to be referring to the same issue, but neither the question nor the answers are very clear.

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  • Cross-reference js-object variables when creating object

    - by Ivar Bonsaksen
    Summary: I want to know if it is possible to do something like this: {a: 'A',b: this.a} ...by using some other pointer like {a: 'A',b: self.a} or {a: 'A',b: own.a} or anything else... Full question: I'm trying to extend MyBaseModule using Ext.extend, and need to cross-reference values in the extension object passed to Ext.extend(). Since I'm not yet in context of MyModule, I'm not able to use this to reference the object (See example below line 12). Is there any other way to reference values like this without creating the object first? 1 MyModule = Ext.extend(MyBaseModule, { 2 dataStores: { 3 myDataStore: new Ext.data.Store({...}) 4 }, 5 6 myGridDefinition: { 7 id: 'myGridDefinitionPanel', 8 bodyBorder: false, 9 items: [{ 10 xtype: 'grid', 11 id: 'myGridDefinitionGrid', 12 store: this.dataStores.myDataStore 13 }] 14 } 15 }); Or is the following the only solution? I would like to avoid this if possible, as I find it less readable for large extension definitions. 1 var extensionObject = { 2 dataStores: { 3 myDataStore: new Ext.data.Store({...}) 4 }, 5 6 myGridDefinition: { 7 id: 'myGridDefinitionPanel', 8 bodyBorder: false, 9 items: [{ 10 xtype: 'grid', 11 id: 'myGridDefinitionGrid' 12 }] 13 } 14 }; 15 16 extensionObject.locationsGrid.items[0].store = extensionObject.dataStores.locations; 17 18 MyModule = Ext.extend(MyBaseModule, extensionObject);

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  • What scenarios are possible where the VS C# compiler would not compile a reference of a reference?

    - by SuperKing
    Hello, I'm probably asking this question wrong (and that may be why Google isn't helping), but here goes: In Visual Studio I am compiling a C# project (let's call it Project A, the startup project) which has a reference to Project B. Project B has a reference to a Project C, so when A gets built, the dlls for B gets placed in the bin directory of A, as does the dll for C (because B requires C, and A requires B). However, I have apparently made some change recently so that the dll for Project C does not go into the bin directory of Project A when rebuilding the solution. I have no idea what I've done to make this happen. I have not modified the setup of the solution itself, and I have only added additional references to the project files. Code wise, I have commented out most of the actual code in Project B that references classes in Project C, but did not remove the reference from the project itself (I don't think this matters). I was told that perhaps the C# compiler was optimizing somehow so that it was not building Project C, but really I'm out of ideas. I would think someone has run into something similar before Any thoughts? Thanks!

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  • Circular Reference exception with JSON Serialisation with MVC3 and EF4 CTP5w

    - by nakchak
    Hi I'm having problems with a circular reference when i try and serialise an object returned via EF4 CTP5. Im using the code first approach and simple poco's for my model. I have added [ScriptIgnore] attributes to any properties that provide a back references to an object and annoyingly every seems to work fine if i manually instantiate the poco's, i.e. they serialise to JSON fine, and the scriptignore attribute is acknowledged. However when i try and serialise an object returned from the DAL i get the circular reference exception "A circular reference was detected while serializing an object of type 'System.Data.Entity.DynamicProxies.xxxx'" I have tried several ways of retreiving the data but they all get stuck with this error: public JsonResult GetTimeSlot(int id) { TimeSlotDao tsDao = new TimeSlotDao(); TimeSlot ts = tsDao.GetById(id); return Json(ts); } The method below works slightly better as rather than the timeslot dynamic proxied object causing the circular refference its the appointment object. public JsonResult GetTimeSlot(int id) { TimeSlotDao tsDao = new TimeSlotDao(); var ts = from t in tsDao.GetQueryable() where t.Id == id select new {t.Id, t.StartTime, t.Available, t.Appointment}; return Json(ts); } Any ideas or solutions to this problem? Update I would prefer to use the out of the box serialiser if possible although Json.Net via nuget is ok as an alternative i would hope its possible to use it as I intended as well...

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  • Reference a GNU C DLL built in GCC against Cygwin, from C#/NET

    - by Dale Halliwell
    Here is what I want: I have a huge legacy C/C++ codebase written for POSIX, including some very POSIX specific stuff like pthreads. This can be compiled on Cygwin/GCC and run as an executable under Windows with the Cygwin DLL. What I would like to do is build the codebase itself into a Windows DLL that I can then reference from C# and write a wrapper around it to access some parts of it programatically. I have tried this approach with the very simple "hello world" example at http://www.cygwin.com/cygwin-ug-net/dll.html and it doesn't seem to work. #include <stdio.h> extern "C" __declspec(dllexport) int hello(); int hello() { printf ("Hello World!\n"); return 42; } I believe I should be able to reference a DLL built with the above code in C# using something like: [DllImport("kernel32.dll")] public static extern IntPtr LoadLibrary(string dllToLoad); [DllImport("kernel32.dll")] public static extern IntPtr GetProcAddress(IntPtr hModule, string procedureName); [DllImport("kernel32.dll")] public static extern bool FreeLibrary(IntPtr hModule); [UnmanagedFunctionPointer(CallingConvention.Cdecl)] private delegate int hello(); static void Main(string[] args) { var path = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "helloworld.dll"); IntPtr pDll = LoadLibrary(path); IntPtr pAddressOfFunctionToCall = GetProcAddress(pDll, "hello"); hello hello = (hello)Marshal.GetDelegateForFunctionPointer( pAddressOfFunctionToCall, typeof(hello)); int theResult = hello(); Console.WriteLine(theResult.ToString()); bool result = FreeLibrary(pDll); Console.ReadKey(); } But this approach doesn't seem to work. LoadLibrary returns null. It can find the DLL (helloworld.dll), it is just like it can't load it or find the exported function. I am sure that if I get this basic case working I can reference the rest of my codebase in this way. Any suggestions or pointers, or does anyone know if what I want is even possible? Thanks.

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  • Update Web Reference in Visual Studio

    - by NeilD
    Hi, I have inherited a web site project that makes use of a number of WCF Web Services hosted on a BizTalk server. We have two environments that I need to deploy this project to, with different URLs for the different BizTalk servers. i.e. In the Staging environment, I need to point the services at xx.xx.xx.101 In the Live environment, I need to point them at xx.xx.xx.102, or whatever. Currently, we've got all of the URLs stored in keys in the web.config file, so that we can change them dynamically... Unfortunately this isn't working! If I change the URL in the web.config to something other than what the project was compiled with, I get an error when calling the service: Server did not recognize the value of HTTP Header SOAPAction: xx.xx.xx.101\ServiceName\MethodName I'm told that the only way they've known to deploy this is to update the web.config URLs, change all of the web references in Visual Studio to match, click on "update web reference" for each reference in Visual Studio, and then compile. It's driving me mad! I've written a pre-build NAnt script to go through and replace all instances of the URL found anywhere in the project directory, and even that isn't making any difference. There must be something else being pulled down from the service when I click the "update reference", but I'm new to working with web services, and so I'm not sure what. Does anyone have any ideas? Is there a way to do this programatically? Thanks.

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  • Does this copy the reference or the object?

    - by Water Cooler v2
    Sorry, I am being both thick and lazy, but mostly lazy. Actually, not even that. I am trying to save time so I can do more in less time as there's a lot to be done. Does this copy the reference or the actual object data? public class Foo { private NameValueCollection _nvc = null; public Foo( NameValueCollection nvc) { _nvc = nvc; } } public class Bar { public static void Main() { NameValueCollection toPass = new NameValueCollection(); new Foo( toPass ); // I believe this only copies the reference // so if I ever wanted to compare toPass and // Foo._nvc (assuming I got hold of the private // field using reflection), I would only have to // compare the references and wouldn't have to compare // each string (deep copy compare), right? } I think I know the answer for sure: it only copies the reference. But I am not even sure why I am asking this. I guess my only concern is, if, after instantiating Foo by calling its parameterized ctor with toPass, if I needed to make sure that the NVC I passed as toPass and the NVC private field _nvc had the exact same content, I would just need to compare their references, right?

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  • Specifying a DLL reference

    - by Jesse
    I'm having trouble setting the path to a DLL that is not in the same directory as the executable. I have a reference to dllA.dll. At present, everything is just copied into the same directory and all is well; however, I need to move the executable to another directory while still referencing the DLL in the original directory. So, it's setup like: C:\Original\Dir program.exe dllA.dll dllB.dll dllC.dll But I need to have it setup like: C:\New\Dir program.exe dllB.dll dllC.dl Such that it is still able to reference dllA.dll in C:\Original\dir I tried the following, but to no avail: Set the "Copy Local" value to false for dllA.dll because I want it to be referenced in its original location. Under "Tools Options Projects and Solutions VC++ Directories" I have added the path to "C:\Original\Dir" Added "C:\Original\Dir" to both the PATH and LIB environment variables At runtime, it informs me that it cannot locate dllA.dll Maybe the above steps I took only matter at compile time? I was able to find this http://stackoverflow.com/questions/1382704/c-specifying-a-location-for-dll-reference But I was thinking that my above method should've worked. Any ideas?

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