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• Help needed in grokking password hashes and salts

  - by javafueled

  I've read a number of SO questions on this topic, but grokking the applied practice of storing a salted hash of a password eludes me. Let's start with some ground rules: a password, "foobar12" (we are not discussing the strength of the password). a language, Java 1.6 for this discussion a database, postgreSQL, MySQL, SQL Server, Oracle Several options are available to storing the password, but I want to think about one (1): Store the password hashed with random salt in the DB, one column Found on SO and elsewhere is the automatic fail of plaintext, MD5/SHA1, and dual-columns. The latter have pros and cons MD5/SHA1 is simple. MessageDigest in Java provides MD5, SHA1 (through SHA512 in modern implementations, certainly 1.6). Additionally, most RDBMSs listed provide methods for MD5 encryption functions on inserts, updates, etc. The problems become evident once one groks "rainbow tables" and MD5 collisions (and I've grokked these concepts). Dual-column solutions rest on the idea that the salt does not need to be secret (grok it). However, a second column introduces a complexity that might not be a luxury if you have a legacy system with one (1) column for the password and the cost of updating the table and the code could be too high. But it is storing the password hashed with a random salt in single DB column that I need to understand better, with practical application. I like this solution for a couple of reasons: a salt is expected and considers legacy boundaries. Here's where I get lost: if the salt is random and hashed with the password, how can the system ever match the password? I have theory on this, and as I type I might be grokking the concept: Given a random salt of 128 bytes and a password of 8 bytes ('foobar12'), it could be programmatically possible to remove the part of the hash that was the salt, by hashing a random 128 byte salt and getting the substring of the original hash that is the hashed password. Then re hashing to match using the hash algorithm...??? So... any takers on helping. :) Am I close?

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• Problem with signals and slots

  - by Jen

  I am creating a class with custom slots in Qt: class CustomEdit : public QTextEdit { Q_OBJECT public: CustomEdit(QWidget* parent); public slots: void onTextChanged (); }; However, I'm getting thise linker error: undefined reference to 'vtable for CustomEdit' The documentation says: if you get compiler errors along the lines of "undefined reference to vtable for LcdNumber", you have probably forgotten to run the moc or to include the moc output in the link command. ... but it is not obvious what that means. Is there something I need to add to my class, or to the .pro file?

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• Table valued function only returns CLR error

  - by Anthony

  I have read-only access to a database that was set up for a third-party, closed-source app. Once group of (hopefully) useful table functions only returns the error: Failed to initialize the Common Language Runtime (CLR) v2.0.50727 with HRESULT 0x80131522. You need to restart SQL server to use CLR integration features. (severity 16) But in theory, the third-party app should be able to use the function (either directly or indirectly), so I'm convinced I'm not setting things up right. I'm very new to SQL Server, so I could be missing something obvious. Or I could be missing something really slight, I have no idea. Here is an example of a query that returns the above error: SELECT * FROM dbo.UncompressDataDateRange(4,'Apr 24 2010 12:00AM','Apr 30 2010 12:00AM') Where the function takes three parameters: The Data Set (int) -- basically the data has 6 classifications, and the giant table this should be pulling from has a column to indicate which is which. startDate (smalldatetime) endDate (smalldatetime) There are other, similar functions that expand on the same idea, all returning the same error. Quick Note: I'm not sure if this is relevant, but I was able to connect to the database via SQL Studio (but without the privs to script the functions as code), and a checked the dependency for the above sample function. It turns out that it is a dependent of a view that I have gotten to work, and that view is dependent of the larger, much-hairier data-table. This makes me think I should somehow be pointing the function at the results of the view, but I'm not seeing any documentation that shows how that is done.

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• Intel Assembler optimization

  - by Søren Haagerup

  I'm currently trying to optimize the code emitted from a home-made compiler, for a home-made language. I've tried out Intel VTune to see where the bottlenecks are: http://www.imada.sdu.dk/~sorenh07/misc/vtune-assembly-optimization.png I find it very impressive that a "subl"-instruction is responsible for over 38% of the clockticks in a program running for 30-90 seconds! Can anybody give an explanation why? The "optimization report" feature in VTune apparently doesn't exist for programs not compiled with icc. Does there exist a program which suggests optimization for assembler code? (that is, not code coming from a high-level language).

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• Operator precedence and struct definition in C

  - by Yktula

  struct struct0 { int a; }; struct struct1 { struct struct0 structure0; int b; } rho; &rho->structure0; /* Reference 1 */ (struct struct0 *)rho; /* Reference 2 */ (struct struct0)rho; /* Reference 3 */ From reference 1, does the compiler take the address of rho, and then access structure0, or vice-versa? What does the line at reference 2 do? Since structure0 is the first member of struct1, would reference 3 be equivalent to reference 1?

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• C# Language Design: explicit interface implementation of an event

  - by ControlFlow

  Small question about C# language design :)) If I had an interface like this: interface IFoo { int Value { get; set; } } It's possible to explicitly implement such interface using C# 3.0 auto-implemented properties: sealed class Foo : IFoo { int IFoo.Value { get; set; } } But if I had an event in the interface: interface IFoo { event EventHandler Event; } And trying to explicitly implement it using field-like event: sealed class Foo : IFoo { event EventHandler IFoo.Event; } I will get the following compiler error: error CS0071: An explicit interface implementation of an event must use event accessor syntax I think that field-like events is the some kind of dualism for auto-implemented properties. So my question is: what is the design reason for such restriction done?

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• All possible values of int from the smallest to the largest, using Java.

  - by Totophil

  Write a program to print out all possible values of int data type from the smallest to the largest, using Java. Some notable solutions as of 8th of May 2009, 10:44 GMT: 1) Daniel Lew was the first to post correctly working code. 2) Kris has provided the simplest solution for the given problem. 3) Tom Hawtin - tackline, came up arguably with the most elegant solution. 4) mmyers pointed out that printing is likely to become a bottleneck and can be improved through buffering. 5) Jay's brute force approach is notable since, besides defying the core point of programming, the resulting source code takes about 128 GB and will blow compiler limits. As a side note I believe that the answers do demonstrate that it could be a good interview question, as long as the emphasis is not on the ability to remember trivia about the data type overflow and its implications (that can be easily spotted during unit testing), or the way of obtaining MAX and MIN limits (can easily be looked up in the documentation) but rather on the analysis of various ways of dealing with the problem.

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• Is a confirmation screen necessary for an order form?

  - by abeger

  In a discussion about how to streamline an order form on our site, the idea of eliminating the confirmation screen. So, instead of filling out the form, clicking "Submit", seeing a summary on a confirmation screen and clicking "Confirm", the user would simply fill out the form, hit "Submit", and the order's done. The theory is that fewer clicks and fewer screens means less time to order and therefore the ordering experience is easier. The opposing opinion says that without the confirmation screen, user error increases and people just end up canceling/changing orders after the fact. I'm looking for more input from the SO community. Have you ever done this? How has it worked out, compared to a traditional confirmation screen setup? Are there examples of a true "one click and done" setup on the web (does Amazon's 1-click have a confirmation screen? I've never been courageous enough to try it)? EDIT: Just to clarify, when I say "confirmation screen", I mean a second step where the customer reviews the order before placing it. Even if we did do away with it, the user would still receive a message saying "your order has been placed".

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• How do I work with WIndows Forms in WPF?

  - by xarzu

  How do I work with WIndows Forms in WPF? In my WPF program I created a Windows Form class. In this Form, I placed an OK button and I went into the properties of the button and set the DialogResult to OK. Now, I am calling this Dialog (Window Form) from the MainWindow.xaml.cs: dres = form.ShowDialog(); if (dres != DialogResult.OK) return; The compiler is complaining: Error 3 'System.Nullable<bool>' does not contain a definition for 'OK' and no extension method 'OK' accepting a first argument of type 'System.Nullable<bool>' could be found (are you missing a using directive or an assembly reference?)

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• HTTP POST prarameters order / REST urls

  - by pq

  Let's say that I'm uploading a large file via a POST HTTP request. Let's also say that I have another parameter (other than the file) that names the resource which the file is updating. The resource cannot be not part of the URL the way you can do it with REST (e.g. foo.com/bar/123). Let's say this is due to a combination of technical and political reasons. The server needs to ignore the file if the resource name is invalid or, say, the IP address and/or the logged in user are not authorized to update the resource. Looks like, if this POST came from an HTML form that contains the resource name first and file field second, for most (all?) browsers, this order is preserved in the POST request. But it would be naive to fully rely on that, no? In other words the order of HTTP parameters is insignificant and a client is free to construct the POST in any order. Isn't that true? Which means that, at least in theory, the server may end up storing the whole large file before it can deny the request. It seems to me that this is a clear case where RESTful urls have an advantage, since you don't have to look at the POST content to perform certain authorization/error checking on the request. Do you agree? What are your thoughts, experiences?

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• Reliable portability for C code without relying on the preprocessor

  - by Yktula

  Relying on the preprocessor and predefined compiler macros for achieving portability seems hard to manage. What's a better way to achieve portability for a C project? I want to put environment-specific code in headers that behave the same way. Is there a way to have the build environment choose which headers to include? I was thinking that I'd put the environment-specific headers into directories for specific environments. The build environment would then just copy the headers from the platform's directory into the root directory, build the project, and then remove the copies.

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• Linux core dumps are too large!

  - by themoondothshine

  Hey guys, Recently I've been noticing an increase in the size of the core dumps generated by my application. Initially, they were just around 5MB in size and contained around 5 stack frames, and now I have core dumps of 2GBs and the information contained within them are no different from the smaller dumps. Is there any way I can control the size of core dumps generated? Shouldn't they be at least smaller than the application binary itself? Binaries are compiled in this way: Compiled in release mode with debug symbols (ie, -g compiler option in GCC). Debug symbols are copied onto a separate file and stripped from the binary. A GNU debug symbols link is added to the binary. At the beginning of the application, there's a call to setrlimit which sets the core limit to infinity -- Is this the problem?

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• Can obfuscation (proguard) lead to MIDlet malfunction?

  - by eMgz

  Hi, Im trying to obfuscate a Java MIDlet with proguard. It runs ok on the PC, however, when I run it on the phone, the program opens, connects to the server, and then freezes. If I disable obfuscation, it runs ok again on the phone. Ive tryed all the obfuscation levels for apps (7, 8 and 9 at NetBeans), and none of them seems to work properly, and I cant release this app for comercial use without obfuscation. Also, the compiler throws some warnings: Note: duplicate definition of library class [java.io.ByteArrayOutputStream] Note: there were 14 duplicate class definitions. But I dont know if this is realy the problem. Does anyone knows what is wrong? The obfuscator arguments are listed below: Obfuscator Arguments (7): -dontusemixedcaseclassnames -default package '' -keep public class ** { public *; } Obfuscator Arguments (8): same as (7) plus -overloadaggressively. Obfuscator Arguments (9): same as (8) but -keep public class ** extends javax.microedition.midlet.MIDlet { public *; } instead. Thanks.

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• sOperator as and generic classes

  - by abatishchev

  I'm writing .NET On-the-Fly compiler for CLR scripting and want execution method make generic acceptable: object Execute() { return type.InvokeMember(..); } T Execute<T>() { return Execute() as T; /* doesn't work: The type parameter 'T' cannot be used with the 'as' operator because it does not have a class type constraint nor a 'class' constraint */ // also neither typeof(T) not T.GetType(), so on are possible return (T) Execute(); // ok } But I think operator as will be very useful: if result type isn't T method will return null, instead of an exception! Is it possible to do?

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• Will more CPUs/cores help with VS.NET build times?

  - by LoveMeSomeCode

  I was wondering if anyone knew whether Visual Studio .NET had a parallel build process or not? I have a solution with lots of projects, every project has lots of markup/code, lots of types, etc. Just sitting there with intellisense on runs it up to about 700MB. But the build times are really slow and only seem to max out one of my two cpu cores. Does this mean the build process is single threaded? My solution's build dependency chain isn't linear, so I don't see why it couldn't be building some of the projects in parallel. I remember Joel Spolsky blogging about his new SSD, and how it didn't help with compile times, but he didn't mention which compiler he was using. We're using VS 2005. Anyone know how it's compilation works? And is it any different/better in 2008/2010?

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• ::LookupAccountSid API Extremely Slow When Targetting x64 Platform (Windows 7)

  - by Chris

  During our application startup, we are making a call to ::LookupAccountSid(). When I build targetting the x86 architecture, this call is nearly instantaneous. However, when I target x64 (debug or release), the call generally takes over 40s to complete. Since this is occurring during application startup, the result is fairly unpleasant as it will appear to the user that the application is not launching. I am running Windows 7 Professional 64-bit on a Dell Studio XPS 16 (Intel Core i7 Q 720). Our application is a native Windows application written in C++. My compiler options (CCOPTS) and linker options (LINKOPTS) are as follows: CCOPTS = "/nologo /Gz /W3 /EHs /c /DWIN32 /D_MBCS /Ob1 /vmg /vmv /Zi /MD /DNDEBUG /DDV_BUILD_DLL /DIV_BUILD_DLL /DDVASSERT_EXCEPTION /Zc:wchar_t-" LINKOPTS = "/manifest:no /nologo /machine:X64 kernel32.lib user32.lib gdi32.lib winspool.lib comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib uuid.lib odbc32.lib odbccp32.lib /DEBUG /subsystem:windows /DLL" Any help would be greatly appreciated :D Thanks, --Chris

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• Static libraries, dynamic libraries, DLLs, entry points, headers ... how to get out of this alive?

  - by tunnuz

  Hello, I recently had to program C++ under Windows for an University project, and I'm pretty confused about static and dynamic libraries system, what the compiler needs, what the linker needs, how to build a library ... is there any good document about this out there? I'm pretty confused about the *nix library system as well (so, dylibs, the ar tool, how to compile them ...), can you point a review document about the current library techniques on the various architectures? Note: due to my poor knowledge this message could contain wrong concepts, feel free to edit it. Thank you Feel free to add more reference, I will add them to the summary. References Since most of you posted *nix or Windows specific references I will summarize here the best ones, I will mark as accepted answer the Wikipedia one, because is a good start point (and has references inside too) to get introduced to this stuff. Program Library Howto (Unix) Dynamic-Link Libraries (from MSDN) (Windows) DLL Information (StackOverflow) (Windows) Programming in C (Unix) An Overview of Compiling and Linking (Windows)

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• What is faster- Java or C# (Or good old C)?

  - by Rexsung

  I'm currently deciding on a platform to build a scientific computational product on, and am deciding on either C#, Java, or plain C with Intels compiler on Core2 Quad CPU's. It's mostly integer arithmetic. My benchmarks so far show Java and C are about on par with each other, and dotNET/C# trails by about 5%- however a number of my coworkers are claiming that dotNET with the right optimizations will beat both of these given enough time for the JIT to do its work. I always assume that the JIT would have done it's job within a few minutes of the app starting (Probably a few seconds in my case, as it's mostly tight loops), so I'm not sure whether to believe them Can anyone shed any light on the situation? Would dotNET beat Java? (Or am I best just sticking with C at this point?). The code is highly multithreaded and data sets are several terabytes in size. Haskell/erlang etc are not options in this case as there is a significant quantity of existing legacy C code that will be ported to the new system, and porting C to Java/C# is a lot simpler than to Haskell or Erlang. (Unless of course these provide a significant speedup). Edit: We are considering moving to C# or Java because they may, in theory, be faster. Every percent we can shave off our processing time saves us tens of thousands of dollars per year. At this point we are just trying to evaluate whether C, Java, or c# would be faster.

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• Returning structs in registers - ARM ABI in GCC

  - by jbcreix

  Hi, In the ARM ABI documentation I come across functions defined like: __value_in_regs struct bar foo(int a, int b) { ... } but GCC(4.3.3) doesn't allow it and all I could find are references to some RealView compiler. Is there any way of doing this from GCC? I have tried -freg-struct-return but it doesn't make a difference. As it is an ABI I can't change the original programs, and returning a regular struct mangles the stack. I would rather not using assembly for this if avoidable as it isn't otherwise necessary. Thanks!

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• Java: Local Enums

  - by bruno conde

  Today, I found myself coding something like this ... public class LocalEnums { public LocalEnums() { } public void foo() { enum LocalEnum { A,B,C }; // .... // class LocalClass { } } } and I was kind of surprised when the compiler reported an error on the local enum: The member enum LocalEnum cannot be local Why can't enums be declared local like classes? I found this very useful in certain situations. In the case I was working, the rest of the code didn't need to know anything about the enum. Is there any structural/design conflict that explains why this is not possible or could this be a future feature of Java?

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• Getting started with massive data

  - by Max

  I'm a math guy and occasionally do some statistics/machine learning analysis consulting projects on the side. The data I have access to are usually on the smaller side, at most a couple hundred of megabytes (and almost always far less), but I want to learn more about handling and analyzing data on the gigabyte/terabyte scale. What do I need to know and what are some good resources to learn from? Hadoop/MapReduce is one obvious start. Is there a particular programming language I should pick up? (I primarily work now in Python, Ruby, R, and occasionally Java, but it seems like C and Clojure are often used for large-scale data analysis?) I'm not really familiar with the whole NoSQL movement, except that it's associated with big data. What's a good place to learn about it, and is there a particular implementation (Cassandra, CouchDB, etc.) I should get familiar with? Where can I learn about applying machine learning algorithms to huge amounts of data? My math background is mostly on the theory side, definitely not on the numerical or approximation side, and I'm guessing most of the standard ML algorithms don't really scale. Any other suggestions on things to learn would be great!

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• Documentation generator for Google Closure Javascript

  - by Julius Eckert

  I want to generate a HTML-Documentation for my Javascript code. The comments in my code are written in a format, the Google Closure Compiler can use to optimize my code. Example: /** * Class for handling timing events. * * @param {number=} opt_interval Number of ms between ticks (Default: 1ms). * @param {Object=} opt_timerObject An object that has setTimeout, setInterval, * clearTimeout and clearInterval (eg Window). * @constructor * @extends {goog.events.EventTarget} */ goog.Timer = function(opt_interval, opt_timerObject) { ... } I am looking for something like http://yardoc.org for Javascript. What tools can you recommend? Are there any specific tools for Google Closure code?

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• Debugging unexpected error message - possible memory management problem?

  - by Ben Packard

  I am trying to debug an application that is throwing up strange (to my untutored eyed) errors. When I try to simply log the count of an array... NSLog(@"Array has %i items", [[self startingPlayers] count]); ...I sometimes get an error: -[NSCFString count]: unrecognized selector sent to instance 0x1002af600 or other times -[NSConcreteNotification count]: unrecognized selector sent to instance 0x1002af600 I am not sending 'count' to any NSString or NSNotification, and this line of code works fine normally. A Theory... Although the error varies, the crash happens at predictable times, immediately after I have run through some other code where I'm thinking I might have a memory management issue. Is it possible that the object reference is still pointing to something that is meant to be destroyed? Sorry if my terms are off, but perhaps it's expecting the array at the address it calls 'count' on, but finds another previous object that shouldn't still be there (eg an NSString)? Would this cause the problem? If so, what is the most efficient way to debug and find out what is that address? Most of my debugging up until now involves inserting NSLogs, so this would be a good opportunity to learn how to use the debugger.

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• Adding Java packages to GWT

  - by Organiccat

  I've tried searching but couldn't come up with a defined way on how to add your own packages to a GWT project. My tree structure looks like this: -com.mycompany -public MyApplication.html MyApplication.gwt.xml -com.mycompany.client MyApp.java -com.mycompany.gui TableLayout.java The answer I've seen out there says to add the packages relative to the root directory of the gwt.xml file, like so: <module> <inherits name="com.google.gwt.user.User" /> <entry-point class="com.mycompany.client.MyApp" /> <source path="client" /> <source path="gui" /> </module> It then complains: Unable to find type 'com.technicon.client.MyApp' Hint: Previous compiler errors may have made this type unavailable Hint: Check the inheritance chain from your module; it may not be inheriting a required module or a module may not be adding its source path entries properly Can anyone tell me what I'm doing wrong and how to fix this?

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• When using the getInstance() method of the abstract java.text.NumberFormat class, what is the actual

  - by iamchuckb

  This question expands upon the one at abstract-class-numberformat-very-confused-about-getinstance. I feel that this question is different enough to merit being asked on its own. In the answers to that question, it was stated that a code statement such as NumberFormat en = NumberFormat.getInstance(Locale.US); returns an object that is a subclass of the java.text.NumberFormat class. It makes sense to me why the return type can't be just an instance of NumberFormat since that is an abstract class. Rather, it was stated that the returned object is at least an instance of NumberFormat, but actually something else. My question is this: what specifically is the class of the object that is returned? In the Sun documentation the only subclasses I see are ChoicesFormat and DecimalFormat. Is there some sort of behind the scenes compiler voodoo going on here? Thanks in advance!

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