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  • What does it mean to pass a &variable to a function? E.g., string& insert ( size_t pos1, const strin

    - by Bob Montgomery
    I understand passing a pointer, and returning a pointer: char * strcat ( char * destination, const char * source ); You're passing a variable that contains the address to a char; returning the same. But what does it mean to pass something using the reference operator? Or to return it? string& insert ( size_t pos1, const string& str ); I mean, I understand what actually happens, I just don't understand the notation. Why isn't the notation this instead: string * insert ( size_t pos1, const string * str ); //made up I presume it has something to do with passing/returning the instance of a class, but what? Is this syntax valid; if not why not and if so what does it mean? char & strcat ( char & destination, const char & source ); //made up (all of the function declarations, except the last made-up two, are from http://www.cplusplus.com )

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  • How to store and remove dynamically and automatic variable of generic data type in custum list data

    - by Vineel Kumar Reddy
    Hi I have created a List data structure implementation for generic data type with each node declared as following. struct Node { void *data; .... .... } So each node in my list will have pointer to the actual data(generic could be anything) item that should be stored in the list. I have following signature for adding a node to the list AddNode(struct List *list, void* eledata); the problem is when i want to remove a node i want to free even the data block pointed by *data pointer inside the node structure that is going to be freed. at first freeing of datablock seems to be straight forward free(data) // forget about the syntax..... But if data is pointing to a block created by malloc then the above call is fine....and we can free that block using free function int *x = (int*) malloc(sizeof(int)); *x = 10; AddNode(list,(void*)x); // x can be freed as it was created using malloc what if a node is created as following int x = 10; AddNode(list,(void*)&x); // x cannot be freed as it was not created using malloc Here we cannot call free on variable x!!!! How do i know or implement the functionality for both dynamically allocated variables and static ones....that are passed to my list.... Thanks in advance...

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  • Do variable references (alias) incure runtime costs in c++?

    - by cheshirekow
    Maybe this is a compiler specific thing. If so, how about for gcc (g++)? If you use a variable reference/alias like this: int x = 5; int& y = x; y += 10; Does it actually require more cycles than if we didn't use the reference. int x = 5; x += 10; In other words, does the machine code change, or does the "alias" happen only at the compiler level? This may seem like a dumb question, but I am curious. Especially in the case where maybe it would be convenient to temporarily rename some member variables just so that the math code is a little easier to read. Sure, we're not exactly talking about a bottleneck here... but it's something that I'm doing and so I'm just wondering if there is any 'actual' difference... or if it's only cosmetic.

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  • Why is my element variable always null in this foreach loop?

    - by ZeroDivide
    Here is the code: public IEnumerable<UserSummary> getUserSummaryList() { var db = new entityContext(); List<UserSummary> model = new List<UserSummary>(); List<aspnet_Users> users = (from user in db.aspnet_Users select user).ToList<aspnet_Users>(); foreach (aspnet_Users u in users) //u is always null while users is a list that contains 4 objects { model.Add(new UserSummary() { UserName = u.UserName, Email = u.aspnet_Membership.Email, Role = Roles.GetRolesForUser(u.UserName).First(), AdCompany = u.AD_COMPANIES.ad_company_name != null ? u.AD_COMPANIES.ad_company_name : "Not an Advertiser", EmployeeName = u.EMPLOYEE.emp_name != null ? u.EMPLOYEE.emp_name : "Not an Employee" }); } return model; } For some reason the u variable in the foreach loop is always null. I've stepped through the code and the users collection is always populated. The table entity for db.aspnet_Users is the users table that comes with asp.net membership services. I've only added a couple associations to it. edit : image of debugger

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  • Is there a better way to keep track of session variable creation/access throughout different pages?

    - by Brandon
    Here's what I am working on. At my website I have multiple processes with each one containing multiple steps. Now in one of the processes, there is an error checking routine executed before proceeding to the next step of that process. A session var is set indicating the error status and it will either redirect back to the referrer or display the next page's contents. Now this kind of functionality, I believe, is common throughout web development. The issue that is occurring is that session vars are left around and are not being cleaned up properly. At times this introduces undesired behavior. My website is growing and I find that I am requiring more and more session vars to keep track of different system and error states. So I was thinking about creating a kind of "session variable keeper" to keep track of session var usage. The idea is fairly simple. It will have the notion of a context (e.g. registration process) and allow access to a predefined set of session vars within that context. In addition, the var and context will be paired with an action to proceed to some form of event handling. So if you haven't noticed I'm new to web development. Any thoughts or comments on the idea that I am proposing would be greatly appreciated. The back-end is written in PHP/MySQL.

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  • Best way to carry & modify a variable through various instances and functions?

    - by bobsoap
    I'm looking for the "best practice" way to achieve a message / notification system. I'm using an OOP-based approach for the script and would like to do something along the lines of this: if(!$something) $messages->add('Something doesn\'t exist!'); The add() method in the messages class looks somewhat like this: class messages { public function add($new) { $messages = $THIS_IS_WHAT_IM_LOOKING_FOR; //array $messages[] = $new; $THIS_IS_WHAT_IM_LOOKING_FOR = $messages; } } In the end, there is a method in which reads out $messages and returns every message as nicely formatted HTML. So the questions is - what type of variable should I be using for $THIS_IS_WHAT_IM_LOOKING_FOR? I don't want to make this use the database. Querying the db every time just for some messages that occur at runtime and disappear after 5 seconds just seems like overkill. Using global constants for this is apparently worst practice, since constants are not meant to be variables that change over time. I don't even know if it would work. I don't want to always pass in and return the existing $messages array through the method every time I want to add a new message. I even tried using a session var for this, but that is obviously not suited for this purpose at all (it will always be 1 pageload too late). Any suggestions? Thanks!

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  • I have a question about variable release in global class.

    - by Beomseok
    + (void)findAndCopyOfDatabaseIfNeeded{ NSArray *path = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [path objectAtIndex:0]; NSFileManager *fileManager = [NSFileManager defaultManager]; NSString *databasePath = [documentsDirectory stringByAppendingPathComponent:@"DB"]; BOOL success = [fileManager fileExistsAtPath:databasePath]; if(!success){ NSString *resourcePath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"DB"]; [fileManager copyItemAtPath:resourcePath toPath:databasePath error:NULL]; } NSString *tracePath = [documentsDirectory stringByAppendingPathComponent:@"Trace"]; BOOL traceDir = [fileManager fileExistsAtPath:tracePath]; if(!traceDir){ NSString *resourcePath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"Trace"]; [fileManager copyItemAtPath:resourcePath toPath:tracePath error:NULL]; } NSDateFormatter *dateFormatter = [[NSDateFormatter alloc]init]; [dateFormatter setDateFormat:@"yyyy"]; NSDate *today = [[NSDate alloc]init]; NSString *resultYear = [dateFormatter stringFromDate:today]; NSString *traceYearPath = [tracePath stringByAppendingPathComponent:resultYear]; BOOL yearDir = [fileManager fileExistsAtPath:tracePath]; if (!yearDir) { [fileManager createDirectoryAtPath:traceYearPath attributes:nil]; } //[resultYear release]; ? //[today release]; ? //[dateFormatter release]; ? } I'm using global class like this [ + (void)findAndCopyOfDatabaseIfNeeded ]. hm,, I don't know NSArray, NSString and NSFileManager are released. Variable release or Not release ? please advice for me.

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  • Mulitple variable containing "for loop" is not working in my code...

    - by OM The Eternity
    Below is the code I am working with and the last for loop i am iterating is not working... I think i am doing something wrong using multiple variable in a for loop,also I m aware of the fact that it can be done. $updaterbk = "SELECT j1. * FROM jos_audittrail j1 LEFT OUTER JOIN jos_audittrail j2 ON ( j1.trackid != j2.trackid AND j1.field != j2.field AND j1.changedone < j2.changedone ) WHERE j1.operation = 'UPDATE' AND j2.id IS NULL "; $selectupdrbk = mysql_query($updaterbk); while($row1 = mysql_fetch_array($selectupdrbk)) { $updrbk[] = $row1; } foreach($updrbk as $upfield) { if(!in_array($upfield['field'],$exist)) { $exist[] = $upfield['field']; $existval[] = $upfield['oldvalue']; //echo $updqueryrbk = "UPDATE `".$upfield['table_name']."` SET "; } } print_r($existval); for($i=0;$j=0;$i<count($exist);$j<count($existval);$i++;$j++) { $updqueryrbk.= $exist[$i]['field']."=".$existval[$j]['oldvalue'].","; $updqueryrbk.="="; $updqueryrbk.= $existval[$j]['oldvalue']; $updqueryrbk.=","; }

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  • Using a variable derived from a drop-down list as the column name in a select statement ... Access DB

    - by user1459698
    I'm working with the world's worst DB that was already here so don't blame me for that. So, here's what I have so far ... module = txtModule.value presstype = txtPressType.value SQL_query = "SELECT * FROM tbl_spareparts WHERE '"& module &"' <> '""' AND '"& module &"' = '"& presstype &"' AND Manufacturer = '"& txtsrch.value &"' ORDER BY SAP_Part_No" Set rsData = conn.Execute(SQL_query) This brings up the following SQL statement: SELECT * FROM tbl_spareparts WHERE 'Banyan_Module' <> '"' AND 'Banyan_Module' = 'PB' AND Manufacturer = 'Tester' ORDER BY SAP_Part_No Is there any way I can use the module variable as a column name - obviously the ''s around the column name are causing an error. This is really bothering me. BTW, I'm writing this in VBScript inside a .HTA application page as it has to run locally on tech PCs. Thanks. R.

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  • Can a T-SQL variable represent an entire row?

    - by elbillaf
    I'm coding for MS SQL Server 10. I have two databases that contain dozens of tables. Each table in one database contains a table with the same name in the other database. Tables with the same name have identical format (fields and data types). The contents of the two tables are similar but not identical. I need to update one based on changes made to the other, but only under certain circumstances. I think I want to use a cursor for this, but I can't find a good example to go by. So far, the MSDN examples are reading one field at a time into a variable. I do need to be able to read /modify two fields which are identical in each table, but I gotta believe there's something less tedious than declaring variables for every field of every table. I would like to be able to FETCH an entire row, check a couple of fields and then make a decision of whether I want to write the entire row to the other table after changing two fields - but do I have to declare variables for EVERY field I want to fetch / write? There's no way to just FETCH an entire row and write an entire row?

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  • Javascript int variable from ASP.NET MVC Model data?

    - by Anders Svensson
    I need to get model data into a javascript variable and use it as an int to compare values. But I can only figure out how to get the model data as strings, otherwise the compiler complains. So how can I get the max and taskBudgetHours as int variables in the Javascript? <script type="text/javascript"> $(document).ready(function () { $("#taskForm").submit(function (e) { var taskBudgetHours = $('#BudgetHours').val(); var max = '<%: Model.Project.RemainingBudgetHours %>'; var test = 'test'; alert(taskBudgetHours); alert(max); if (taskBudgetHours <= max) { //This doesn't work, seems to treat it as strings... return true; } else { //Prevent the submit event and remain on the screen e.preventDefault(); alert('There are only ' + max + ' hours left of the project hours.'); return false; } }); return; }); </script>

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  • Mongodb, linq driver. How to construct Contains with variable or statements

    - by Syska
    I'm using the LINQ Driver for C#, works great. Sorting a lot of properties but heres a problem I can't solve, its probebly simple. var identifierList = new []{"10", "20", "30"}; var newList = list.Where(x => identifierList.Contains(x.Identifier)); This is NOT supported ... So I could do something like: var newList = list.Where(x => x.Identifier == "10" || x.Identifier == "20" || x.Identifier == "30"); But since the list is variable ... how do I construct the above? Or are there even better alternatives? The list is of type IQueryable<MyCustomClass> For information ... this is used as a filter of alot of properties. In SQL I could have a parent - child relationship. But as I can't as the parent for the main ID I need to take all the ID's out and then construct it like this. Hopes this makes sense. If needed I will explain more.

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  • C++: Static variable inside a constructor, are there any drawbacks or side effects?

    - by doc
    What I want to do: run some prerequisite code whenever instance of the class is going to be used inside a program. This code will check for requiremts etc. and should be run only once. I found that this can be achieved using another object as static variable inside a constructor. Here's an example for a better picture: class Prerequisites { public: Prerequisites() { std::cout << "checking requirements of C, "; std::cout << "registering C in dictionary, etc." << std::endl; } }; class C { public: C() { static Prerequisites prerequisites; std::cout << "normal initialization of C object" << std::endl; } }; What bothers me is that I haven't seen similar use of static variables so far. Are there any drawbacks or side-effects or am I missing something? Or maybe there is a better solution? Any suggestions are welcome.

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  • How to use a variable in a function expression which is injected in a page?

    - by anonymous
    I'm trying to inject a function into a webpage via Chrome extension content script by: function inject(code) { var actualCode = '(' + code + ')();'; var script = document.createElement('script'); script.textContent = actualCode; (document.head||document.documentElement).appendChild(script); script.parentNode.removeChild(script); } var myObj = person; // myObj/person is passed in from elsewhere var fn = function() { alert(myObj.name); }; inject(fn); // myObj undefined My issue is, since fn is a function expression, I can't pass in myObj.personName. So my question is, how can I construct a function expression that includes a variable? Do I do some sort of string concatenation instead? I also tried to pass the object to the function, as follows: function inject(code, myObj) { var actualCode = '(' + code + ')(' + myObj +');'; ... But this did not work, and caused a "Uncaught SyntaxError: Unexpected identifier" error. Related: Building a Chrome Extension - Inject code in a page using a Content script

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  • MATLAB: What is an appropriate Data Structure for a Matrix with Random Variable Entries?

    - by user568249
    I'm currently working in an area that is related to simulation and trying to design a data structure that can include random variables within matrices. To motivate this let me say I have the following matrix: [a b; c d] I want to find a data structure that will allow for a, b, c, d to either be real numbers or random variables. As an example, let's say that a = 1, b = -1, c = 2 but let d be a normally distributed random variable with mean 0 and SD 1. The data structure that I have in mind will give no value to d. However, I also want to be able to design a function that can take in the structure, simulate an uniform(0,1), obtain a value for d using an inverse CDF and then spit out an actual matrix. I have several ideas to do this (all related to the MATLAB icdf function) but would like to know how more experienced programmers would do this. In this application, it's important that the structure is as "lean" as possible since I will be working with very very large matrices and memory will be an issue.

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  • (iphone) How to access CGRect member variable inside c++ class?

    - by Eugene
    i have a c++ class with CGrect variable and i'm getting segfault when trying to access it. class Parent { //with some virtual functions/dtors }; class Child { public: void SetRect(CGRect rect) { mRect = rect; } CGRect GetRect() { return mRect; } int GetIndex() { return mIndex; } private: CGRect mRect; int mIndex; }; i'm doing CGRect rect = childPtr->GetRect(); from object c code and it segfaults. I printed *childPtr just before the call and rect looks fine with intended data value. int index = childPtr->GetIndex(); from same object c code(*.mm), works fine though. Any idea why I'm getting segfaults? Thank you edit - It's got something to do with virtual functions. (gdb) p singlePuzzlePiece-GetRect() Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_PROTECTION_FAILURE at address: 0x00000001 0x00000001 in ?? () Cannot access memory at address 0x1 The program being debugged was signaled while in a function called from GDB. GDB remains in the frame where the signal was received. To change this behavior use "set unwindonsignal on" Evaluation of the expression containing the function (at 0x1) will be abandoned. (gdb) Somehow, the function is not properly compiled?

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  • Why does Java think my object is a variable?

    - by user2896898
    Ok so I'm trying to make a simple pong game. I have a paddle that follows the mouse and a ball that bounces around. I wrote a method collidesWith(Sprite s) inside of my Sprite class that checks if the ball collides with the paddle (this works and isn't the problem). I have two objects extending my sprite class, a ball and a paddle object. So inside of my ball class I'm trying to check if it collides with the paddle. So I've tried if(this.collidesWith(paddle) == true){ System.out.println("They touched"); } I've also tried ball.collidesWith(paddle) and other combinations but it always says the same thing about the paddle (and the ball when I use ball.collidesWith) "Cannot find symbol. Symbol: variable paddle(or ball). Location: class Ball" So if I'm reading this right, it thinks that the paddle (and ball) are variables and it's complaining because it can't find them. How can I make it understand I am passing in objects, not variables? For extra information, an earlier assignment had me make two boxes and for them to change colors when they were colliding. In that assignment I used very similar code to above with if(boxOne.collidesWith(boxTwo) == true){ System.out.println("yes"); } And in this code it worked just fine. The program knew that boxOne and boxTwo were child classes of my Sprite class. Anyone know why they wouldn't work the same?

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  • Why would ssh fail to expand %h variable in .ssh/config?

    - by Zoran
    Why would ssh fail to expand %h from .ssh/config? This used to work and still works except on a RHEL box. Looking for what the origin of this could be. Is there a setting somewhere that tells ssh to not expand %h? I have something like this in my .ssh/config: Host *.foo HostName %h.mydomain.com On the RHEL box where this doesn't work, I get this: $ ssh -vvvv bar.foo OpenSSH_5.3p1, OpenSSL 1.0.0-fips 29 Mar 2010 debug1: Reading configuration data /home/zsimic/.ssh/config debug1: Applying options for *.foo debug1: Applying options for *.foo debug1: Applying options for * debug1: Reading configuration data /etc/ssh/ssh_config debug1: Applying options for * debug2: ssh_connect: needpriv 0 ssh: Could not resolve hostname %h.mydomain.com: Name or service not known

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  • How well will ntpd work when the latency is highly variable?

    - by JP Anderson
    I have an application where we are using some non-standard networking equipment (cannot be changed) that goes into a dormant state between traffic bursts. The network latency is very high for the first packet since it's essentially waking the system, waiting for it to reconnect, and then making the first round-trip. Subsequent messages (provided they are within the next minute or so) are much faster, but still highly-latent. A typical set of pings will look like 2500ms, 900ms, 880ms, 885ms, 900ms, 890ms, etc. Given that NTP uses several round trips before computing the offset, how well can I expect ntpd to work over this kind of link? Will the initially slow first round trip be ignored based on the much different (and faster) following messages to/from the ntp server? Thanks and Regards.

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  • In Puppet, how would I secure a password variable (in this case a MySQL password)?

    - by Beaming Mel-Bin
    I am using Puppet to provision MySQL with a parameterised class: class mysql::server( $password ) { package { 'mysql-server': ensure => installed } package { 'mysql': ensure => installed } service { 'mysqld': enable => true, ensure => running, require => Package['mysql-server'], } exec { 'set-mysql-password': unless => "mysqladmin -uroot -p$password status", path => ['/bin', '/usr/bin'], command => "mysqladmin -uroot password $password", require => Service['mysqld'], } } How can I protect $password? Currently, I removed the default world readable permission from the node definition file and explicitly gave puppet read permission via ACL. I'm assuming others have come across a similar situation so perhaps there's a better practice.

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  • Can I save an Apache environment variable value with SetEnv?

    - by Nicholas Tolley Cottrell
    I am running Apache 2.2 with Tomcat 6 and have several layers of URL rewriting going on in both Apache with RewriteRule and in Tomcat. I want to pass through the original REQUEST_URI that Apache sees so that I can log it properly for "page not found" errors etc. In httpd.conf I have a line: SetEnv ORIG_URL %{REQUEST_URI} and in the mod_jk.conf, I have: JkEnvVar ORIG_URL Which i thought should make the value available via request.getAttribute("ORIG_URL") in Servlets. However, all that I see is "%{REQUEST_URI}", so I assume that SetEnv doesn't interpret the %{...} syntax. What is the right way to get the URL the user requested in Tomcat?

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  • How do I reference the value of a constructed environment variable in a loop?

    - by Rob Spieldenner
    What I'm trying to do is loop over environment variables. I have a number of installs that change and each install has 3 IPs to push files to and run scripts on, and I want to automate this as much as possible (so that I only have to modify a file that I'll source with the environment variables). The following is a simplified version that once I figure out I can solve my problem. So given in my.props: COUNT=2 A_0=foo B_0=bar A_1=fizz B_1=buzz I want to fill in the for loop in the following script #!/bin/bash . <path>/my.props for ((i=0; i < COUNT; i++)) do <script here> done So that I can get the values from the environment variables. Like the following(but that actually work): echo $A_$i $B_$i or A=A_$i B=B_$i echo $A $B returns foo bar then fizz buzz

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  • How do I read multiple lines from STDIN into a variable?

    - by The Wicked Flea
    I've been googling this question to no avail. I'm automating a build process here at work, and all I'm trying to do is get version numbers and a tiny description of the build which may be multi-line. The system this runs on is OSX 10.6.8. I've seen everything from using CAT to processing each line as necessary. I can't figure out what I should use and why. Attempts read -d '' versionNotes Results in garbled input if the user has to use the backspace key. Also there's no good way to terminate the input as ^D doesn't terminate and ^C just exits the process. read -d 'END' versionNotes Works... but still garbles the input if the backspace key is needed. while read versionNotes do echo " $versionNotes" >> "source/application.yml" done Doesn't properly end the input (because I'm too late to look up matching against an empty string).

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  • How to reference individual cells in Excel to variable data from records in an external SQL table

    - by user273476
    I have a SQL table containing date oriented financial data eg. multiple daily records with fields for Date, Account code and Value. I want to set up dynamic links (formulas) from cells in an Excel speadsheet to this data so when the spreadsheet is loaded the data is fetched from all the relevant records. The spreadsheet has the Account codes on the x axis and Dates on the y. Each day the SQL table has new data in it for the new day and I want the spreadsheet to reference this new data for the column for the new day. Any ideas? I have seen how you can generally bring in data from a SQL table (in our case using ODBC as it is not MS SQL) but the data is not simply bringing in multiple records as you would a CVS file but specific records in the SQL table referencing to specific cells and columns in the spreadsheet.

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