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• Java Thread - Synchronization issue

  - by Yatendra Goel

  From Sun's tutorial: Synchronized methods enable a simple strategy for preventing thread interference and memory consistency errors: if an object is visible to more than one thread, all reads or writes to that object's variables are done through synchronized methods. (An important exception: final fields, which cannot be modified after the object is constructed, can be safely read through non-synchronized methods, once the object is constructed) This strategy is effective, but can present problems with liveness, as we'll see later in this lesson. Q1. Is the above statements mean that if an object of a class is going to be shared among multiple threads, then all instance methods of that class (except getters of final fields) should be made synchronized, since instance methods process instance variables?

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• Why use constants in programming?

  - by Adam N

  I've just been going back over a bit of C studying using Ivor Horton's Beginning C book. I got to the bit about declaring constants which seems to get mixed up with variables in the same sentence. Just to clarify, what is the difference in specifying constants and variables in C, and really, when do you need to use a constant instead of a variable? I know folks say to use a constant when the information doesn't change during program execution but I can't really think of a time when a variable couldn't be used instead. Thanks

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• Rails Variable across all controller actions

  - by bob

  Hello, This should be a very simple rails question. I have a variable like the following. @administration = Administration.first I want this variable to be accessible through every controller action across all my controllers so for example if I have a Product controller and inside of it I have the usual CRUD actions, I want the @administration variable as defined above to be put into all the CRUD actions. (It would not be needed in destroy or create or update). I have many controllers throughout my project and I was wondering if there is an easier way than adding it manually through all of the actions that I want it in. I tried a global variable $administration = Administration.first but I run into an issue where it is not updated when I update the actual content of the Administration.first table. Also, I would like to avoid global variables. Any help would be much appreciated. Thanks! :)

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• method returning wrong variable

  - by cocoanewbie

  This class I'm working with has three instance variables I'm interested in, NSmutablearrays xArray yArray and zArray, there are also other NSmutablearrays, a, bArray and c. I just added accessors - (NSMutableArray *) xArray { return xArray; } ditto for y and z. However, it's returning yArray, zArray and bArray for some reason. Why is that happening? Okay, I just changed the names of the methods to GetXArray and everything seems to be returning the right variables. Now I'm really confused. How the heck did this happen and how do I prevent this from happening in the future?

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• How to use the variable declared in one class in another class in Obj C.

  - by srikanth rongali

  I have a NSDate *date1 in class1 implementation file(I initialized it as Global variable). I have NSDate *date2 in class 2 implementation file (initialized it as Global variable). I need to calculate the NSTimeInterval between the two dates in class 2. But I could not do it. I could not access date1 in this class. It is giving error as (date2 undeclared). Please give me help in how to call other class variables in this class. Thank you.

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• please help please

  - by davit-datuashvili

  http://stackoverflow.com/questions/2836934/how-to-compare-two-char-variables please show me a few steps how to start to write this code please

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• C# Different class objects in one list

  - by jeah_wicer

  I have looked around some now to find a solution to this problem. I found several ways that could solve it but to be honest I didn't realize which of the ways that would be considered the "right" C# or OOP way of solving it. My goal is not only to solve the problems but also to develop a good set of code standards and I'm fairly sure there's a standard way to handle this problem. Let's say I have 2 types of printer hardwares with their respective classes and ways of communicating: PrinterType1, PrinterType2. I would also like to be able to later on add another type if neccessary. One step up in abstraction those have much in common. It should be possible to send a string to each one of them as an example. They both have variables in common and variables unique to each class. (One for instance communicates via COM-port and has such an object, while the other one communicates via TCP and has such an object). I would however like to just implement a List of all those printers and be able to go through the list and perform things as "Send(string message)" on all Printers regardless of type. I would also like to access variables like "PrinterList[0].Name" that are the same for both objects, however I would also at some places like to access data that is specific to the object itself (For instance in the settings window of the application where the COM-port name is set for one object and the IP/port number for another). So, in short something like: In common: Name Send() Specific to PrinterType1: Port Specific to PrinterType2: IP And I wish to, for instance, do Send() on all objects regardless of type and the number of objects present. I've read about polymorphism, Generics, interfaces and such, but I would like to know how this, in my eyes basic, problem typically would be dealt with in C# (and/or OOP in general). I actually did try to make a base class, but it didn't quite seem right to me. For instance I have no use of a "string Send(string Message)" function in the base class itself. So why would I define one there that needs to be overridden in the derived classes when I would never use the function in the base class ever in the first place? I'm really thankful for any answers. People around here seem very knowledgeable and this place has provided me with many solutions earlier. Now I finally have an account to answer and vote with too. EDIT: To additionally explain, I would also like to be able to access the objects of the actual printertype. For instance the Port variable in PrinterType1 which is a SerialPort object. I would like to access it like: PrinterList[0].Port.Open() and have access to the full range of functionality of the underlaying port. At the same time I would like to call generic functions that work in the same way for the different objects (but with different implementations): foreach (printer in Printers) printer.Send(message)

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• static effect on python

  - by fatai

  how we can construct static effect on python instead of using class and global ? not like that one : global a a = [] #simple ex ; fonk ( a , b , d) x = 1 a.append ( x) EDIT: I want to create temporary memory , if I exit the function namely fonk , I want to save change as list on temporary memory . We can do that demand only put static keyword in front of data type but in python , we dont have static, so I want that effect in python . Therefore , how can I do ? As above code say "a" represents temporary memory

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• Lua operations, that works in mutitheaded environment

  - by SBKarr

  My application uses Lua in multithreaded environment with global mutex. It implemented like this: Thread locks mutex, Call lua_newthread Perform some initialization on coroutine Run lua_resume on coroutine Unlocks mutex lua_lock/unlock is not implemented, GC is stopped, when lua works with coroutine. My question is, can I perform steps 2 and 3 without locking, if initialisation process does not requires any global Lua structs? Can i perform all this process without locking at all, if coroutine does not requires globals too? In what case I generally can use Lua functions without locking?

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• Why do I get strange output from Perl using SQL?

  - by benjamin button

  Here is my Perl code: foreach my $line (@tmp_field_validation) { chomp $line; my ($cycle_code,$cycle_month,$cycle_year)= split /\s*\|\s*/, $line; $cycle_code=~ s/^\s*(.*)\s*$/$1/; $cycle_month=~ s/^\s*(.*)\s*$/$1/; $cycle_year=~ s/^\s*(.*)\s*$/$1/; print "$line\n"; print "$cycle_code|$cycle_month|$cycle_year"; } Here is the output: 1 10 2009 1 10 2009|| What's wrong over here? I expected the pipes to be between the variables. Why are the pipes getting printed after all the three variables?

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• Member variable in C++ class that is always constant for all objects of that class?

  - by user1799323

  I'm constructing a class where I have three member variables that I want to always be the same value NO MATTER WHAT. I have class foo{ public: double var_1, var_2, var_3; double x=1, y=2, z=3; [functions go here] }; that gave me an error since I can't initialize a variable like that. But I want x, y and z to always be 1, 2 and 3 respectively. I tried defining them outside the class but that doesn't work since I want them to be member variables of the class. How do I do this?

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• .htaccess stupid issue

  - by justnoone

  I have a server where I can only configure httpd using .htaccess, a cannot access global configuration. I want to rewrite almost every non-existing path to index.php, so I did something like: RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d RewriteRule ^(.*)$ index.php?path=$1 [L,QSA] And that is ok. But another thing I want to do is to prevent access to path where I keep PHP files (I cannot store them somewhere else) which is for example /php. I would like that anything starting with /php rewrites to index.php?path=php... so I did something like: RewriteCond %{REQUEST_URI} ^/php.* RewriteRule ^(.*)$ /index.php?path=$1 [L,QSA] And that also would work ok if I had access to global configuration. In case of per-directory configuration, when I access /php it rewrites it to index.php?path=php and than puts directory name before that: /php/index.php?path=php. I read documentation and I realize that it uses internal redirects when per-directory confoguration is used. How can I avoid this behavior?

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• Find a variable with a given value in VS2008

  - by Aaron

  I have an instance variable with several members, many of which have their own members and so on. Using the debugger and watch variables, I found a string variable with a specific value that I need by diving into this variable's members. However, after spending some time on other things and coming back to this, I am now unable to find where this value is located. When I have my application paused, is there a way to search the values of variables in the current context for a given value? To clarify, if I have the given structure: myVariable | |--aMember1 | |--subMember = "A value" | |--aMember2 |--subMember = "Another value" Is there a way (possibly using the watch list in VS debugger) to search myVariable for any member or submember with the value "A value", returning to me the path myVariable->aMember->subMember?

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• Which is the best Linux C/C++ debugger (or front-end to gdb) to help teaching programming?

  - by omer.gimenez

  I teach a sort of "lite" C++ programming course to novices ("lite" meaning no pointers, no classes, just plain old C, plus references and STL string and vectors). Students have no previous experience in programming, so I believe that using an interactive debugger would help them understand program flow, variables, and recursion. The course is taught in Linux. Teaching them to use gdb is just overkill (they will not use nor understand most features). I just need something simple but easy to use: to see at which line the program is now, what is in the stack (local variables, previous calls, etc.). I look something similar to old Turbo Pascal or Turbo C++ Borland's debugger, or Visual Studio debugger. Thank you,

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• Call an anonymous function defined in a setInterval

  - by Tominator

  Hi, I've made this code: window.setInterval(function(){ var a = doStuff(); var b = a + 5; }, 60000) The actual contents of the anonymous function is of course just for this small example as it doesn't matter. What really happens is a bunch of variables get created in the scope of the function itself, because I don't need/want to pollute the global space. But as you all know, the doStuff() function won't be called until 60 seconds in the page. I would also like to call the function right now, as soon as the page is loaded, and from then on every 60 seconds too. Is it somehow possible to call the function without copy/pasting the inside code to right after the setInterval() line? As I said, I don't want to pollute the global space with useless variables that aren't needed outside the function.

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• Performance implications of using a variable versus a magic number

  - by Nathan

  I'm often confused by this. I've always been taught to name numbers I use often using variables or constants, but if it reduces the efficiency of the program, should I still do it? Heres an example: private int CenterText(Font font, PrintPageEventArgs e, string text) { int recieptCenter = 125; int stringLength = Convert.ToInt32(e.Graphics.MeasureString(text, font)); return recieptCenter - stringLength / 2; } The above code is using named variables, but runs slower then this code: private int CenterText(Font font, PrintPageEventArgs e, string text) { return 125 - Convert.ToInt32(e.Graphics.MeasureString(text, font) / 2); } In this example, the difference in execution time is minimal, but what about in larger blocks of code?

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• How do make dependency generation work for C? (Also..decode this sed/make statement!)

  - by Derek

  Hi all. I have a make build system that I am trying to decipher that someone else wrote. I am getting an error when I run it on a redhat system, but not when I run it on my solaris system. The versions of gmake are the same major revision (one off on minor revision). This is for building a C project, and the make system has a global Makefile.global that is inherited by each directory's local Makefile The Makefile.global has all the targets in it, starting with all: $(LIB) $(BIN) where LIB builds libs and BIN builds binaries. jumping down the targets I have $(LIB) : $(GEN_LIB) $(GEN_LIB) : $(GEN_DEPS) $(GEN_OBJS) $(AR) $(ARFLAGS) $(GEN_LIB) $(GEN_OBJS) $(GEN_DEPS) : @set -e; rm -f $@; \ $(CC) $(CDEP_FLAG) $(CFLAGS) $(INCDIRS) `basename $@ | sed 's/\.d/\.c/' | sed 's,^,$(HOME_SRC)/,'` | sed 's,\(.*\)\.o: ,$(GEN_OBJDIR)/\1.o $@ :,g' > [email protected] ; \ cat [email protected] > $@ ; \ cat [email protected] | cut -d: -f2 | grep '\.h' | sed 's,\.h,.h :,g' >> $@ ; \ rm [email protected] $(GEN_OBJS) : $(CC) $(CFLAGS) $(INCDIRS) -c $(*F).c -lmpi -o $@ I think these are all the relevant targets I need to include to answer my question. Definitions of those variables: CC = icc CDEP_FLAG = -M CFLAGS = various compiler flags ifdef type flags INCDIRS = include directory where all .h files are GEN_OBJDIR = /lib/objs HOME_SRC = . GEN_LIB = lib/$(LIB) GEN_DEPDIR=/lib/deps GEN_DEPS = $(addprefix $(GEN_DEPDIR)/,$(addsuffix .d,$(basename $(OBJS)))) I think this has everything covered you need. Basically self explanatory from the names. Now as best I can tell, this is generating in /lib/deps a .d file that has the object and source dependencies in it. In other words, for the utilities.a library, I will get a utils.o and utils.c dependency stack, all in the file utils.d There is some syntax error that is being generated in that file I think, because I get the following error: ../lib/deps/util.d:25: *** target pattern contains no '%'. Stop. gmake[2]: *** [all] Error 2 gmake[1]: *** [all] Error 2 gmake: *** [all] Error 2 I am not sure if my error is in the dependency generation, or some further down part, like the object generation target? If you need further info, let me know, I will add to post

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• Is it OK to put a standard, pure C header #include directive inside a namespace?

  - by mic_e

  I've got a project with a class log in the global namespace (::log). So, naturally, after #include <cmath>, the compiler gives an error message each time I try to instantiate an object of my log class, because <cmath> pollutes the global namespace with lots of three-letter methods, one of them being the logarithm function log(). So there are three possible solutions, each having their unique ugly side-effects. Move the log class to it's own namespace and always access it with it's fully qualified name. I really want to avoid this because the logger should be as convenient as possible to use. Write a mathwrapper.cpp file which is the only file in the project that includes <cmath>, and makes all the required <cmath> functions available through wrappers in a namespace math. I don't want to use this approach because I have to write a wrapper for every single required math function, and it would add additional call penalty (cancelled out partially by the -flto compiler flag) The solution I'm currently considering: Replace #include <cmath> by namespace math { #include "math.h" } and then calculating the logarithm function via math::log(). I have tried it out and it does, indeed, compile, link and run as expected. It does, however, have multiple downsides: It's (obviously) impossible to use <cmath>, because the <cmath> code accesses the functions by their fully qualified names, and it's deprecated to use in C++. I've got a really, really bad feeling about it, like I'm gonna get attacked and eaten alive by raptors. So my question is: Is there any recommendation/convention/etc that forbid putting include directives in namespaces? Could anything go wrong with diferent C standard library implementations (I use glibc), different compilers (I use g++ 4.7, -std=c++11), linking? Have you ever tried doing this? Are there any alternate ways to banish the math functions from the global namespace? I've found several similar questions on stackoverflow, but most were about including other C++ headers, which obviously is a bad idea, and those that weren't made contradictory statements about linking behaviour for C libraries. Also, would it be beneficial to additionally put the #include <math.h> inside extern "C" {}?

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• How to setup Math program

  - by Miles

  I'm needing to write a program (C#) that will allow the user to create generic formulas with variables and numbers. For example: D = A + (A - C / X)(7.8 - 6.6) F = E + (E - C / X)(7.8 - 6.6) FinalResult = (A + D)(0.9) + (E + F)(0.32) + B(0.1) + .023 where all variables would mean for me to go to a database and look something up based on values and return a number in its place. So A would be 2.12 for example (and the same for C and E) Whats the best way to structure this program? How would I make my program read these formulas? I've seen a little bit of the MathML but not sure how to get that started (or an example of it)

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• How do game trainers change an address in memory that's dynamic?

  - by GameTrainersWTF

  Lets assume I am a game and I have a global int* that contains my health. A game trainer's job is to modify this value to whatever in order to achieve god mode. I've looked up tutorials on game trainers to understand how they work, and the general idea is to use a memory scanner to try and find the address of a certain value. Then modify this address by injecting a dll or whatever. But I made a simple program with a global int* and its address changes every time I run the app, so I don't get how game trainers can hard code these addresses? Or is my example wrong? What am I missing?

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• How to call a Zend lucene search function?

  - by stef

  I inherited a Zend project devoid of comments and I didn't get to talk to the previous developer. Since I have no Zend experience I'm having some issues :) I'd like to print out some variables inside an function that indexes items from the site using Zend_Search_Lucene because I think something is going wrong here. From what I've read, ::create creates a new index and ::open updates it. So it's in this ::open function I'd like to print out some variables. The name and params of the function are below. Does anyone have any idea how this function can be called so I can run some tests? private function search($category,$string,$page = 1,$itemsByPage = 5) EDIT: OR, is there a way I can nuke the existing index and force it to be rebuilt completely, for example by deleting the index files on the FS and then performing some searches?

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• Objective C: Can't find .js file in my mainBundle?!

  - by Nic Hubbard

  This is driving me crazy as I cannot figure out what in the world is going on. I load up files form you main bundle all the time, xml files, html files, etc. But, now I am trying to get the contents of a javascript file but it can never find it. I am using: NSData *jsData = [NSData dataWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"global" ofType:@"js"]]; if (jsData) { NSLog(@"%@", jsData); } else { NSLog(@"Can't find file"); return; } Even checking the [[NSBundle mainBundle] pathForResource:@"global" ofType:@"js"] string returns null. My activity.js file is in my Resources folder, the exact location where my other files are location that work totally fine using the above method. Why can't it find my js file?

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• Remembering Form information

  - by Pete Herbert Penito

  Hi everyone! I'm sorry if this has been asked before but I feel my situation is a little different... I have a huge form (like 50 questions involving checkboxes, drop downs, text boxes and textareas) When a user submits a form and the validation page throws an error, is there an easy way to keep the info they entered? My intitial form is on form.php and then the form action is form_posted.php, before anything is run on form_posted.php I have my validation code which sends the user back to form.php with an error number (eg. form.php?error=3) if there was a problem with any in particular. This is done with header("form.php?error=3") so on form.php do the posted variables exist? even tho the page wasn't specifically sent with any posted variables. Also if this is the case, is it completely secure to be making the value of a textbox what it was before? like <input type="text" value="php echo $_POSTED["username"] ?>">

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• Can't find .js file in my mainBundle?!

  - by Nic Hubbard

  This is driving me crazy as I cannot figure out what in the world is going on. I load up files form you main bundle all the time, xml files, html files, etc. But, now I am trying to get the contents of a javascript file but it can never find it. I am using: NSData *jsData = [NSData dataWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"global" ofType:@"js"]]; if (jsData) { NSLog(@"%@", jsData); } else { NSLog(@"Can't find file"); return; } Even checking the [[NSBundle mainBundle] pathForResource:@"global" ofType:@"js"] string returns null. My globaly.js file is in my Resources folder, the exact location where my other files are location that work totally fine using the above method. Why can't it find my js file?

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• Propor usage of double and single quotes?

  - by Phox

  I'm talking about the performance increase here. From all I know you can echo variables in double quotes ("), like so: <?php echo "You are $yourAge years old"; ?> But single quotes will just return You are $yourAge years old. But what about performance differences? I've always gone by the rule that single quotes are faster because the PHP interpreter doesn't have to search through the string for variables. But I'm seeing more and more blog and forum posts on the web saying differently. Does anyone actually have any information on this subject? Perhaps benchmark tests or something? Cheers.

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