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  • Codeigniter/mySQL question. Checking if several inserts are possible before actual insertion.

    - by Ethan
    Hey SO, So I'm trying to perform a couple inserts at once that are kind of co-dependent on each other. Let's say I'm doing a dog rating website. Anyone can add a dog to my database, but in doing so they also need to add a preliminary rating of the dog. Other people can then rate the dog afterwards. The dogs to ratings is a many to one relationship: a dog has many ratings. This means for my preliminary add, since I have the person both rate and add the dog, I need to take the rating, and set a foreign key to the dog's primary key. As far as I know, this means I have to actually add the dog, then check what that new addition's primary key is, and then put that in my rating before insertion. Now suppose something were to go wrong with the rating's insert, be it a string that's too long, or something that I've overlooked somehow. If the rating's failed, the dog has already been inserted, but the rating has not. In this case, I'd like the dog to not have been added in the first place. Does this mean I have to write code that says "if the rating fails, do a remove for the dog," or is there a way to predict what the key will be for the dog should everything go as planned. Is there a way to say "hold that spot," and then if everything works, add it? Any help would be greatly appreciated. Thanks!!

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  • Inline function v. Macro in C -- What's the Overhead (Memory/Speed)?

    - by Jason R. Mick
    I searched Stack Overflow for the pros/cons of function-like macros v. inline functions. I found the following discussion: Pros and Cons of Different macro function / inline methods in C ...but it didn't answer my primary burning question. Namely, what is the overhead in c of using a macro function (with variables, possibly other function calls) v. an inline function, in terms of memory usage and execution speed? Are there any compiler-dependent differences in overhead? I have both icc and gcc at my disposal. My code snippet I'm modularizing is: double AttractiveTerm = pow(SigmaSquared/RadialDistanceSquared,3); double RepulsiveTerm = AttractiveTerm * AttractiveTerm; EnergyContribution += 4 * Epsilon * (RepulsiveTerm - AttractiveTerm); My reason for turning it into an inline function/macro is so I can drop it into a c file and then conditionally compile other similar, but slightly different functions/macros. e.g.: double AttractiveTerm = pow(SigmaSquared/RadialDistanceSquared,3); double RepulsiveTerm = pow(SigmaSquared/RadialDistanceSquared,9); EnergyContribution += 4 * Epsilon * (RepulsiveTerm - AttractiveTerm); (note the difference in the second line...) This function is a central one to my code and gets called thousands of times per step in my program and my program performs millions of steps. Thus I want to have the LEAST overhead possible, hence why I'm wasting time worrying about the overhead of inlining v. transforming the code into a macro. Based on the prior discussion I already realize other pros/cons (type independence and resulting errors from that) of macros... but what I want to know most, and don't currently know is the PERFORMANCE. I know some of you C veterans will have some great insight for me!!

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  • Howto: Access a second related model in a nested attribute builder block

    - by Joe Cairns
    I have a basic has_many through relationship: class Foo < ActiveRecord::Base has_many :bars, :dependent => :destroy has_many :wtfs :through => :bars accepts_nested_attributes_for :bars, :wtfs end On my crud forms I have a builder block for the wtf, but I need the label to come from the bar (an attribute called label for instance). What's the proper method to do this? Here's the most simple scaffold: <h1>New foo</h1> <% form_for(@foo) do |f| %> <%= f.error_messages %> <p> <%= f.label :name %><br /> <%= f.text_field :name %> </p> <h2>Bars</h2> <% f.fields_for :wtfs do |builder| %> <%= builder.hidden_field :bar_id %> <p> <%= builder.text_field :wtf_data_i_need_to_set %> </p> <% end %> <p> <%= f.submit 'Create' %> </p> <% end %> <%= link_to 'Back', foos_path %>

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  • How does windows differentiate between regular exe and a .Net exe?

    - by Yogendra
    Hi All, This might be a duplicate entry. Excuse me if it is. I was asked in an interview as to how does Windows OS differentiate between regular exe and .Net exe. My reply was, when .Net exe is build, the compiler emits some information into the header. The information is PE32 or PE32+. windows verifies the header to determine if it needs to load the MSCOREE.dll which loads the CLR and executes the exe. I am not sure if my answer is correct ? Your inputs is appreciated.

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  • Compilation hangs for a class with field double d = 2.2250738585072012e-308

    - by 01es
    I have come across an interesting situation. A coworker committed some changes, which would not compile on my machine neither from the IDE (Eclipse) nor from a command line (Maven). The problem manifested in the compilation process taking 100% CPU and only killing the process would help to stop it. After some analysis the cause of the problem was located and resolved. It turned out be a line "double d = 2.2250738585072012e-308" (without semicolon at the end) in one of the interfaces. The following snipped duplicates it. public class WeirdCompilationIssue { double d = 2.2250738585072012e-308 } Why would compiler hang? A language edge case?

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  • What could possibly cause this error when declaring an object inside a class?

    - by M4design
    I'm battling with this assignment :) I've got two classes: Ocean and Grid. When I declare an object of the Grid inside the Ocean: unsigned int sharkCount; Grid grid; The compiler/complainer says: error C2146: syntax error : missing ';' before identifier 'grid' Can you possibly predict what produces this error with the limited info I provided? It seems that as if the Ocean doesn't like the Grid class. Could this be because of the poor implementation of the grid class. BTW the Grid has a default constructor. Yet the error happens in compiling time!. EDIT: They're each in separate header file, and I've included the Grid.h in the Ocean.h.

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  • How do you make your Java application memory efficient?

    - by Boune
    How do you optimize the heap size usage of an application that has a lot (millions) of long-lived objects? (big cache, loading lots of records from a db) Use the right data type Avoid java.lang.String to represent other data types Avoid duplicated objects Use enums if the values are known in advance Use object pools String.intern() (good idea?) Load/keep only the objects you need I am looking for general programming or Java specific answers. No funky compiler switch. Edit: Optimize the memory representation of a POJO that can appear millions of times in the heap. Use cases Load a huge csv file in memory (converted into POJOs) Use hibernate to retrieve million of records from a database Resume of answers: Use flyweight pattern Copy on write Instead of loading 10M objects with 3 properties, is it more efficient to have 3 arrays (or other data structure) of size 10M? (Could be a pain to manipulate data but if you are really short on memory...)

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  • Modify bash variables with sed

    - by Alexander Cska
    I am trying to modify a number of environmental variables containing predefined compiler flags. To do so, I tried using a bash loop that goes over all environmental variables listed with "env". for i in $(env | grep ipo | awk 'BEGIN {FS="="} ; { print $1 } ' ) do echo $(sed -e "s/-ipo/ / ; s/-axAVX/ /" <<< $i) done This is not working since the loop variable $i contains just the name of the environmental variable stored as a character string. I tried searching a method to convert a string into a variable but things started becoming unnecessary complicated. The basic problem is how to properly supply the environmental variable itself to sed. Any ideas how to properly modify my script are welcome. Thanks, Alex

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  • How does cast in C#/.NET 3.5 work for types with '?'

    - by Inez
    This is my code which works public decimal? Get() { var res = ... return res.Count() > 0 ? res.First() : (decimal?) null; } and this one doesn't work public decimal? Get() { var res = ... return res.Count() > 0 ? res.First() : null; } giving the compiler error: Error 1 Type of conditional expression cannot be determined because there is no implicit conversion between 'decimal' and '<null>' I wonder why? any ideas?

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  • C static variables and intialization

    - by yCalleecharan
    Hi, If I have a global static variable x like in this code #include <stdio.h> #include <stdio.h> static int x; int main(void) { DO SOMETHING WITH x HERE x++; } What will be difference if I opted to initialize x to a value first say as in static int x = 0; before entering "main"? In my first case where I didn't assign a value to x, does the compiler implicitly know that x is to be set to zero as it's a static variable? I heard that we can do this with static variables. Thanks a lot...

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  • hiding inner class implementation using namespace

    - by Abruzzo Forte e Gentile
    Hi all I am developing a library and a would like to provide my users a public interface separate from the real implementatino that is hidden in a namespace. This way, I could change only the class HiddenQueue without changing myQueue that will be exposed to users only. If I put the C++ code of HiddenQueue in the myQueue.cpp file the compiler complains saying _innerQueue has incomplete type. I thought that the linker was able to resolve this. What I am doing wrong here? Thanks Afg // myQueue.h namespace inner{ class HiddenQueue; }; class myQueue{ public: myQueue(); ); private: inner::HiddenQueue _innerQueue; }; /////////////////////////// // myQueue.cpp namespace inner{ class HiddenQueue{}; };

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  • g++: Use ZIP files as input

    - by Notinlist
    We have the Boost library in our side. It consists of huge amount of files which are not changing ever and only a tiny portion of it is used. We swap the whole boost directory if we are changing versions. Currently we have the Boost sources in our SVN, file by file which makes the checkout operations very slow, especially on Windows. It would be nice if there were a notation / plugin to address C++ files inside ZIP files, something like: // @ZIPFS ASSIGN 'boost' 'boost.zip/boost' #include <boost/smart_ptr/shared_ptr.hpp> Are there any support for compiler hooks in g++? Are there any effort regarding ZIP support? Other ideas?

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  • Why do my WPF UIElements NOT have OnPreview events?

    - by Matt.M
    I'm building a custom Silverlight UserControl which needs to listen to events using Preview/Tunneling, but for some reason the compiler is telling me they are not recognized or accessible. For example, I can add an event handler to MouseLeftButtonDown, but not PreviewMouseLeftButtonDown. This doesn't make sense because according to Microsoft (http://msdn.microsoft.com/en-us/library/system.windows.uielement_members(v=VS.100).aspx) all UIElements should have Preview events attached. Any ideas as to why this is happening? I'm using Visual Studio 2010 Trial, Blend 4 RC and .Net 4, if that makes a difference.

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  • C5 Generics Collection IntervalHeap<T> -- getting an IPriorityQueueHandle from a T for Replace or De

    - by Jared Updike
    I'm using the Generics Collection library C5 (server down :-( ) and I have an IntervalHeap(T) and I need to Delete or Replace a T that is not the Max or Min. How do I get an IPriorityQueueHandle from my T? The C5 library source code shows that IPriorityQueueHandle(T) has no methods or properties to implement and the compiler thinks my implementation of IPriorityQueueHandle(T) for my T is acceptable. I try to use a T like this: q.Replace(t, t); and the C5 library throws an InvalidCastException because it cannot convert my T to a (Handle).

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  • Which language + framework should I use for building standalone clients for my PHP webapp?

    - by Jagira
    Hello, I have a PHP web application which basically maintains a set of user profiles and their records. My users are using the app via browser. I am planning to build a standalone desktop client/app for WINDOWS OS, in which a user can login, retrieve and modify the records. Which language + framework will be simple, fast and lightweight to use? I can think of the following options: Microsoft Visual Basic - simplest? Microsoft Visual C++ Python PHP + bambalam compiler Are there any other options? And which of these is better?

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  • Design pattern: polymorphisim for list of objects

    - by ziang
    Suppose I have a class A, and A1, A2 inherits from A. There are 2 functions: List<A1> getListA1(){...} List<A2> getListA2(){...} Now I want to do something similar to both A1 and A2 in another function public void process(List<A>){...} If I want to pass the instance of either ListA1 or ListA2, of course the types doesn't match because the compiler doesn't allow the coercion from List< A1 to List< A. I can't do something like this: List<A1> listA1 = getListA1(); List<A> newList = (List<A>)listA1; //this is not allowed. So what is the best approach to the process()? Is there any way to do it in a universal way rather than write the similar code to both List and List?

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  • In C#: How to declare a generic Dictionary with a type as key and an enumeration of that type as val

    - by Marcel
    Hi all, I want to declare a dictionary that stores typed IEnumerable's of a specific type, with that exact type as key, like so: (Edited to follow johny g's comment) private IDictionary<Type, IEnumerable<T>> _dataOfType where T: BaseClass; //does not compile! The concrete classes I want to store, all derive from BaseClass, therefore the idea to use it as constraint. The compiler complains that it expects a semicolon after the member name. If it would work, I would expect this would make the later retrieval from the dictionary simple like: IEnumerable<ConcreteData> concreteData; _sitesOfType.TryGetValue(typeof(ConcreteType), out concreteData); How to define such a dictionary?

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  • C++ - defining static const integer members in class definition

    - by HighCommander4
    My understanding is that C++ allows static const members to be defined inside a class so long as it's an integer type. Why, then, does the following code give me a linker error? #include <algorithm> #include <iostream> class test { public: static const int N = 10; }; int main() { std::cout << test::N << "\n"; std::min(9, test::N); } The error I get is: test.cpp:(.text+0x130): undefined reference to `test::N' collect2: ld returned 1 exit status Interestingly, if I comment out the call to std::min, the code compiles and links just fine (even though test::N is also referenced on the previous line). Any idea as to what's going on? My compiler is gcc 4.4 on Linux.

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  • Why "constructor-way" of declaring variable in "for-loop" allowed but in "if-statement" not allowed?

    - by PiotrNycz
    Consider this simple example: /*1*/ int main() { /*2*/ for (int i(7); i;){break;} /*3*/ if (int i(7)) {} /*4*/ } Why line-2 compiles just fine, whilst line-3 gives the error? This is little strange to me why if-statement is in this aspect treated worse than for-loop? If this is compiler specific - I tested with gcc-4.5.1: prog.cpp: In function 'int main()': prog.cpp:3:7: error: expected primary-expression before 'int' prog.cpp:3:7: error: expected ')' before 'int' I was inspired by this question [UPDATE] I know this compiles just fine: /*1*/ int main() { /*2*/ for (int i = 7; i;){break;} /*3*/ if (int i = 7) {} /*4*/ }

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  • Connect to a website via HTTP in C

    - by sfactor
    i have a C code that parses a file and generates another file for the processed data. i now need to send these files to a web server (website). i guess there way is to do a HTTP POST. but i have never done this in c (Linux gcc compiler in ubuntu). Does anyone know how to do this. i need to a starting point as i have no clue of doing this in C. i also need to be able to authenticate with the website.

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  • C++ Header Guard issues

    - by JP
    I am making a small C++ framework, which contains many .h and .cpp. I have created a general include which include all my .h file such as: framework.h #include "A.h" #include "B.h" #include "C.h" each .h header are protected with include guard such as #ifndef A_HEADER #define A_HEADER ... #endif The issues is, I would like to be able to include "framework.h" inside all the sub .h such as, but it cause lots of compiler error: #ifndef A_HEADER #define A_HEADER #include "framework.h" ... #endif If instead I use the real header file for each sub header, and the framework.h for what ever use my framework it works fine.. I would just like to include the main header inside all my sub .h so I dont need to include all the dependency everytime. Thanks :)

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  • Is it possible to come over the time out issue for a function call in C#?

    - by infant programmer
    In my program I call a method xslTransform.Load(strXmlQueryTransformPath, xslSettings, new XmlUrlResolver()); The problem I am facing is: sometimes this function doesn't execute well within the time. Sometimes compiler raises the time out issue after a long time of trial.. which inturn causes this part of application to shut. That is what I want to avoid. So if it exceeds certain time say 10 seconds I need to recall the method. Is it possible to add some code lines adjacent to this, which can meet the requirement?

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  • Can I share code & resources between Android projects without using a library?

    - by Tom
    The standard advice for sharing code & resources between Android projects is to use a library. Personally I find this works poorly if (a) the shared code changes a lot, or (b) your computer isn't fast enough. I also don't want to get into deploying multiple APK's, which seems to be necessary when I use dependent projects (i.e. Java Build Path, Projects Tab). On the other hand, sharing a folder of source code by using the Eclipse linked source feature works great (Java Build Path, Source tab, Link Source button), but for these two issues: 1) I can't use the same technique to share resources. I can create the link to the resources parent folder but then things get wonky and the shared resources don't get compiled (I'm using ADT 21). 2) So then I settle for copying the shared resources into each project, but this doesn't work because either. The shared code can't import the copy of its resources because it doesn't know the package name of the project that uses it. The solution I've been using is to access the resources dynamically, but that has become cumbersome as the number of resources grows. So, I need a solution to either (1) or (2), or I'll have to go back to a library project. (Or maybe there is another option I haven't thought of?)

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  • Accessing subclass members from a superclass pointer C++

    - by Dr. Monkey
    I have an array of custom class Student objects. CourseStudent and ResearchStudent both inherit from Student, and all the instances of Student are one or the other of these. I have a function to go through the array, determine the subtype of each Student, then call subtype-specific member functions on them. The problem is, because these functions are not overloaded, they are not found in Student, so the compiler kicks up a fuss. If I have a pointer to Student, is there a way to get a pointer to the subtype of that Student? Would I need to make some sort of fake cast here to get around the compile-time error?

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  • Global variable not stable after platform changed.

    - by user350555
    Our embedded system is built on a hw/sw platform made by enea. After the platform updated recently, we found some operations on the global variable keep crashing the system. For example, we have a global map structure holding some data. We can insert/iterate the map once or twice, then the address of the elements in the map suddenly changed to some forbidden addresses like 0x0 or 0x1d, the system just crash. The only different before/after the platform update is : 1) sw part: It's a c++ software and We changed the compiler from diab cc to gcc. 2) hw part: we have a new board, but the cpu is still powerpc405s. I tried every possible way but still can't figure out the reason. Any thoughts?

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