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• Memory allocation in case of static variables

  - by eSKay

  I am always confused about static variables, and the way memory allocation happens for them. For example: int a = 1; const int b = 2; static const int c = 3; int foo(int &arg){ arg++; return arg; } How is the memory allocated for a,b and c? What is the difference (in terms of memory) if I call foo(a), foo(b) and foo(c)?

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• Another dynamic memory allocation bug.

  - by m4design

  I'm trying to allocate memory for a multidimensional array (8 rows, 3 columns). Here's the code for the allocation (I'm sure the error is clear for you) char **ptr = (char **) malloc( sizeof(char) * 8); for (i = 0; i < 3; i++) ptr[i] = (char *) malloc( sizeof(char) * 3); The crash happens when I reference this: ptr[3][0]; Unhandled exception at 0x0135144d in xxxx.exe: 0xC0000005: Access violation writing location 0xabababab. Are there any recommended references/readings for this kind of subject? Thanks.

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• Memory allocation for collections in .NET

  - by Yogendra

  This might be a dupe. I did not find enough information on this. I was discussing memory allocation for collections in .Net. Where is the memory for elements allocated in a collection? List<int> myList = new List<int>(); The variable myList is allocated on stack and it references the List object created on heap. The question is when int elements are added to the myList, where would they be created ? Can anyone point the right direction?

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• Unit Testing-- fundamental goal?

  - by David

  Me and my co-workers had a bit of a disagreement last night about unit testing in our PHP/MySQL application. Half of us argued that when unit testing a function within a class, you should mock everything outside of that class and its parents. The other half of us argued that you SHOULDN'T mock anything that is a direct dependancy of the class either. The specific example was our logging mechanism, which happened through a static Logging class, and we had a number of Logging::log() calls in various locations throughout our application. The first half of us said the Logging mechanism should be faked (mocked) because it would be tested in the Logging unit tests. The second half of us argued that we should include the original Logging class in our unit test so that if we make a change to our logging interface, we'll be able to see if it creates problems in other parts of the application due to failing to update the call interface. So I guess the fundamental question is-- do unit tests serve to test the functionality of a single unit in a closed environment, or show the consequences of changes to a single unit in a larger environment? If it's one of these, how do you accomplish the other?

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• C++ operator new, object versions, and the allocation sizes

  - by mizubasho

  Hi. I have a question about different versions of an object, their sizes, and allocation. The platform is Solaris 8 (and higher). Let's say we have programs A, B, and C that all link to a shared library D. Some class is defined in the library D, let's call it 'classD', and assume the size is 100 bytes. Now, we want to add a few members to classD for the next version of program A, without affecting existing binaries B or C. The new size will be, say, 120 bytes. We want program A to use the new definition of classD (120 bytes), while programs B and C continue to use the old definition of classD (100 bytes). A, B, and C all use the operator "new" to create instances of D. The question is, when does the operator "new" know the amount of memory to allocate? Compile time or run time? One thing I am afraid of is, programs B and C expect classD to be and alloate 100 bytes whereas the new shared library D requires 120 bytes for classD, and this inconsistency may cause memory corruption in programs B and C if I link them with the new library D. In other words, the area for extra 20 bytes that the new classD require may be allocated to some other variables by program B and C. Is this assumption correct? Thanks for your help.

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• Is memory allocation in linux non-blocking?

  - by Mark

  I am curious to know if the allocating memory using a default new operator is a non-blocking operation. e.g. struct Node { int a,b; }; ... Node foo = new Node(); If multiple threads tried to create a new Node and if one of them was suspended by the OS in the middle of allocation, would it block other threads from making progress? The reason why I ask is because I had a concurrent data structure that created new nodes. I then modified the algorithm to recycle the nodes. The throughput performance of the two algorithms was virtually identical on a 24 core machine. However, I then created an interference program that ran on all the system cores in order to create as much OS pre-emption as possible. The throughput performance of the algorithm that created new nodes decreased by a factor of 5 relative the the algorithm that recycled nodes. I'm curious to know why this would occur. Thanks. *Edit : pointing me to the code for the c++ memory allocator for linux would be helpful as well. I tried looking before posting this question, but had trouble finding it.

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• Memory allocation for a matrix in C

  - by Snogzvwtr

  Why is the following code resulting in Segmentation fault? (I'm trying to create two matrices of the same size, one with static and the other with dynamic allocation) #include <stdio.h> #include <stdlib.h> //Segmentation fault! int main(){ #define X 5000 #define Y 6000 int i; int a[X][Y]; int** b = (int**) malloc(sizeof(int*) * X); for(i=0; i<X; i++){ b[i] = malloc (sizeof(int) * Y); } } Weirdly enough, if I comment out one of the matrix definitions, the code runs fine. Like this: #include <stdio.h> #include <stdlib.h> //No Segmentation fault! int main(){ #define X 5000 #define Y 6000 int i; //int a[X][Y]; int** b = (int**) malloc(sizeof(int*) * X); for(i=0; i<X; i++){ b[i] = malloc (sizeof(int) * Y); } } or #include <stdio.h> #include <stdlib.h> //No Segmentation fault! int main(){ #define X 5000 #define Y 6000 int i; int a[X][Y]; //int** b = (int**) malloc(sizeof(int*) * X); //for(i=0; i<X; i++){ // b[i] = malloc (sizeof(int) * Y); //} } I'm running gcc on Linux on a 32-bit machine.

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• Unit testing in python?

  - by yossi.ittach

  Hey - I'm new to python , and I'm having a hard time grasping the concept of Unit testing in python. I'm coming from Java - so unit testing makes sense because - well , there you actually have a unit - A Class. But a Python class is not necessarily the same as a Java class , and the way I use Python - as a scripting language - is more functional then OOP - So what do you "unit test" in Python ? A flow? Thanks!

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• Unit testing an iPhone static library with XCode 3

  - by teabot

  I am writing a number of static libraries for the iPhone and wish also to have suites of unit tests. XCode 3 provides templates for both static libraries and unit tests but I am wondering how they should fit together in a static library project? In my static library project I have created a target for unit testing but expect to also create an executable to kick off the unit tests than run against the classes in the static library. What is the procedure for doing this?

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• Are unit tests also used to find bugs?

  - by Draco

  I was reading the following article and the author made it quite clear that unit tests are NOT used to find bugs. I would like to know what your thoughts are on this. I do know that unit tests makes the design of your application much more robust but isn't it the fact that finding bugs through unit tests that make the application robust, besides its other advantages? http://blog.stevensanderson.com/2009/08/24/writing-great-unit-tests-best-and-worst-practises/

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• How to unit test business rules?

  - by Robert Lamb

  I need a unit test to make sure I am accumulating vacation hours properly. But vacation hours accumulate according to a business rule, if the rule changes, then the unit test breaks. Is this acceptable? Should I expose the rule through a method and then call that method from both my code and my test to ensure that the unit test isn't so fragile? My question is: What is the right way to unit test business rules that may change?

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• How do you unit test your T-SQL

  - by AlexKuznetsov

  How do you unit test your T-SQL? Which libraries/tools do you use? What percentage of your code is covered by unit tests and how do you measure it? Do you think the time and effort which you invested in your unit testing harness has paid off or not? If you do not use unit testing, can you explain why not?

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• Is Debug.Assert obsolete if you write unit tests?

  - by Justin Pihony

  Just like the question asks, is there a need to add Debug.Assert into your code if you are writing unit tests (which has its own assertions)? I could see that this might make the code more obvious without having to go into the tests, however it just seems that you might end up with duplicated asserts. It seems to me that Debug.Assert was helpful before unit-testing became more prevalent, but is now unnecessary. Or, am I not thinking of some use case?

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• Should library classes be wrapped before using them in unit testing?

  - by Songo

  I'm doing unit testing and in one of my classes I need to send a mail from one of the methods, so using constructor injection I inject an instance of Zend_Mail class which is in Zend framework. Example: class Logger{ private $mailer; function __construct(Zend_Mail $mail){ $this->mail=$mail; } function toBeTestedFunction(){ //Some code $this->mail->setTo('some value'); $this->mail->setSubject('some value'); $this->mail->setBody('some value'); $this->mail->send(); //Some } } However, Unit testing demands that I test one component at a time, so I need to mock the Zend_Mail class. In addition I'm violating the Dependency Inversion principle as my Logger class now depends on concretion not abstraction. Does that mean that I can never use a library class directly and must always wrap it in a class of my own? Example: interface Mailer{ public function setTo($to); public function setSubject($subject); public function setBody($body); public function send(); } class MyMailer implements Mailer{ private $mailer; function __construct(){ $this->mail=new Zend_Mail; //The class isn't injected this time } function setTo($to){ $this->mailer->setTo($to); } //implement the rest of the interface functions similarly } And now my Logger class can be happy :D class Logger{ private $mailer; function __construct(Mailer $mail){ $this->mail=$mail; } //rest of the code unchanged } Questions: Although I solved the mocking problem by introducing an interface, I have created a totally new class Mailer that now needs to be unit tested although it only wraps Zend_Mail which is already unit tested by the Zend team. Is there a better approach to all this? Zend_Mail's send() function could actually have a Zend_Transport object when called (i.e. public function send($transport = null)). Does this make the idea of a wrapper class more appealing? The code is in PHP, but answers doesn't have to be. This is more of a design issue than a language specific feature

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• TCP Windows Size vs Socket Buffer Size on Windows

  - by Patrick L

  I am new to Windows networking. When people talk about TCP tuning on Windows platform, they always mention about TCP Window Size. I am wondering whether Windows uses the concept of "Socket Buffer Size"? On Windows XP, the TCP window size is fixed. We can set it using the TCPWindowSize registry value. How about Socket Buffer Size? How can we set Socket Buffer size on Windows? Can we set it to a value different from TCP window size?

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• Memory allocation problem with SVMs in OpenCV

  - by worksintheory

  Hi, I've been using OpenCV happily for a while, but now I have a problem which has bugged me for quite some time. The following code is reasonably minimal example of my problem: #include <cv.h> #include <ml.h> using namespace cv; int main(int argc, char **argv) { int sampleCountForTesting = 2731; //BROKEN: Breaks svm.train_auto(...) for values of 2731 or greater! Mat trainingData( sampleCountForTesting, 1, CV_32FC1, Scalar::all(0.0) ); Mat trainingResponses( sampleCountForTesting, 1, CV_32FC1, Scalar::all(0.0) ); for(int j = 0; j < 6; j++) { trainingData.at<float>( j, 0 ) = (float) (j%2); trainingResponses.at<float>( j, 0 ) = (float) (j%2); //Setting a few values so I don't get a "single class" error } CvSVMParams svmParams( 100, //100 is CvSVM::C_SVC, 2, //2 is CvSVM::RBF, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, NULL, TermCriteria( TermCriteria::MAX_ITER | TermCriteria::EPS, 2, 1.0 ) ); CvSVM svm = CvSVM(); svm.train_auto( trainingData, trainingResponses, Mat(), Mat(), svmParams ); return 0; } I just create matrices to hold the training data and responses, then set a few entries to some value other than zero, then run the SVM. But it breaks whenever there are 2731 rows or more: OpenCV Error: One of arguments' values is out of range (requested size is negative or too big) in cvMemStorageAlloc, file [omitted]/opencv/OpenCV-2.2.0/modules/core/src/datastructs.cpp, line 332 With fewer rows, it seems to be fine and a classifier trained in a similar manner to the above seems to be giving reasonable output. Am I doing something wrong? I'm pretty sure it's not actually anything to do with lack of memory, as I've got 6GB and also the code works fine when the data has 2730 rows and 10000 columns, which is a much bigger allocation. I'm running OpenCV 2.2 on OSX 10.6 and initially I thought the problem might be related to this bug if for some reason the fix wasn't included in the MacPorts version. Now I've also tried downloading the most recent stable version from the OpenCV site and building with cmake and using that, but I still get the same error, and the fix is definitely included in that version. Any help would be much appreciated! Thanks,

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• NSXMLParser Memory Allocation Efficiency for the iPhone

  - by Staros

  Hello, I've recently been playing with code for an iPhone app to parse XML. Sticking to Cocoa, I decided to go with the NSXMLParser class. The app will be responsible for parsing 10,000+ "computers", all which contain 6 other strings of information. For my test, I've verified that the XML is around 900k-1MB in size. My data model is to keep each computer in an NSDictionary hashed by a unique identifier. Each computer is also represented by a NSDictionary with the information. So at the end of the day, I end up with a NSDictionary containing 10k other NSDictionaries. The problem I'm running into isn't about leaking memory or efficient data structure storage. When my parser is done, the total amount of allocated objects only does go up by about 1MB. The problem is that while the NSXMLParser is running, my object allocation is jumping up as much as 13MB. I could understand 2 (one for the object I'm creating and one for the raw NSData) plus a little room to work, but 13 seems a bit high. I can't imaging that NSXMLParser is that inefficient. Thoughts? Code... The code to start parsing... NSXMLParser *parser = [[NSXMLParser alloc] initWithData: data]; [parser setDelegate:dictParser]; [parser parse]; output = [[dictParser returnDictionary] retain]; [parser release]; [dictParser release]; And the parser's delegate code... -(void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qualifiedName attributes:(NSDictionary *)attributeDict { if(mutableString) { [mutableString release]; mutableString = nil; } mutableString = [[NSMutableString alloc] init]; } -(void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string { if(self.mutableString) { [self.mutableString appendString:string]; } } -(void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName { if([elementName isEqualToString:@"size"]){ //The initial key, tells me how many computers returnDictionary = [[NSMutableDictionary alloc] initWithCapacity:[mutableString intValue]]; } if([elementName isEqualToString:hashBy]){ //The unique identifier if(mutableDictionary){ [mutableDictionary release]; mutableDictionary = nil; } mutableDictionary = [[NSMutableDictionary alloc] initWithCapacity:6]; [returnDictionary setObject:[NSDictionary dictionaryWithDictionary:mutableDictionary] forKey:[NSMutableString stringWithString:mutableString]]; } if([fields containsObject:elementName]){ //Any of the elements from a single computer that I am looking for [mutableDictionary setObject:mutableString forKey:elementName]; } } Everything initialized and released correctly. Again, I'm not getting errors or leaking. Just inefficient. Thanks for any thoughts!

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• Remove never-run call to templated function, get allocation error on run-time

  - by Narfanator

  First off, I'm a bit at a loss as to how to ask this question. So I'm going to try throwing lots of information at the problem. Ok, so, I went to completely redesign my test project for my experimental core library thingy. I use a lot of template shenanigans in the library. When I removed the "user" code, the tests gave me a memory allocation error. After quite a bit of experimenting, I narrowed it down to this bit of code (out of a couple hundred lines): void VOODOO(components::switchBoard &board){ board.addComponent<using_allegro::keyInputs<'w'> >(); } Fundementally, what's weirding me out is that it appears that the act of compiling this function (and the template function it then uses, and the template functions those then use...), makes this bug not appear. This code is not being run. Similar code (the same, but for different key vals) occurs elsewhere, but is within Boost TDD code. I realize I certainly haven't given enough information for you to solve it for me; I tried, but it more-or-less spirals into most of the code base. I think I'm most looking for "here's what the problem could be", "here's where to look", etc. There's something that's happening during compile because of this line, but I don't know enough about that step to begin looking. Sooo, how can a (presumably) compilied, but never actually run, bit of templated code, when removed, cause another part of code to fail? Error: Unhandled exceptionat 0x6fe731ea (msvcr90d.dll) in Switchboard.exe: 0xC0000005: Access violation reading location 0xcdcdcdc1. Callstack: operator delete(void * pUser Data) allocator< class name related to key inputs callbacks ::deallocate vector< same class ::_Insert_n(...) vector< " " ::insert(...) vector<" "::push_back(...) It looks like maybe the vector isn't valid, because _MyFirst and similar data members are showing values of 0xcdcdcdcd in the debugger. But the vector is a member variable...

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• What's a unit test? [closed]

  - by Tyler

  Possible Duplicates: What is unit testing and how do you do it? What is unit testing? I recognize that to 95% of you, this is a very WTF question. So. What's a unit test? I understand that essentially you're attempting to isolate atomic functionality but how do you test for that? When is it necessary? When is it ridiculous? Can you give an example? (Preferably in C? I mostly hear about it from Java devs on this site so maybe this is specific to Object Oriented languages? I really don't know.) I know many programmers swear by unit testing religiously. What's it all about? EDIT: Also, what's the ratio of time you typically spend writing unit tests to time spent writing new code?

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• Memory allocation in Linux

  - by Goofy

  Hello! I have a multi threaded application where I allocate buffers with data, which then wait in queues to be send via sockets. All buffers are reproducible because I use only buffers of fixed size in whole program (1024, 2048, 2080 and 5248 bytes). I noticed, that my program usually use up to 10 buffers of each length type at the same moment. So far I always manually allocate new buffer and then free it (using malloc() and free ()) where it's not needed any more. I started wondering if Linux is enough smart to cache this memory for me, so next time I allocate new buffer system only quickly receive a buffer I have already used before and not perform heavy operation of allocating new memory block?

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• Is mocking for unit testing appropriate in this scenario?

  - by Vinoth Kumar

  I have written around 20 methods in Java and all of them call some web services. None of these web services are available yet. To carry on with the server side coding, I hard-coded the results that the web-service is expected to give. Can we unit test these methods? As far as I know, unit testing is mocking the input values and see how the program responds. Are mocking both input and ouput values meaningful? Edit : The answers here suggest I should be writing unit test cases. Now, how can I write it without modifying the existing code ? Consider the following sample code (hypothetical code) : public int getAge() { Service s = locate("ageservice"); // line 1 int age = s.execute(empId); // line 2 return age; // line 3 } Now How do we mock the output ? Right now , I am commenting out 'line 1' and replacing line 2 with int age= 50. Is this right ? Can anyone point me to the right way of doing it ?

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• Have unit test generators helped you when working with legacy code?

  - by Duncan Bayne

  I am looking at a small (~70kLOC including generated) C# (.NET 4.0, some Silverlight) code-base that has very low test coverage. The code itself works in that it has passed user acceptance testing, but it is brittle and in some areas not very well factored. I would like to add solid unit test coverage around the legacy code using the usual suspects (NMock, NUnit, StatLight for the Silverlight bits). My normal approach is to start working through the project, unit testing & refactoring, until I am satisfied with the state of the code. I've done this many times in the past, and it's worked well. However, this time I'm thinking of using a test generator (in particular Pex) to create the test framework, then manually fleshing it out. My question is: have you used unit test generators in the past when commencing work on a legacy codebase, and if so, would you recommend them? My fear is that the generated tests will miss the semantic nuances of the code-base, leading to the dreaded situation of having tests for the sake of the coverage metric, rather than tests which clearly express the intended behaviour in code.

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• Practical refactoring using unit tests

  - by awhite

  Having just read the first four chapters of Refactoring: Improving the Design of Existing Code, I embarked on my first refactoring and almost immediately came to a roadblock. It stems from the requirement that before you begin refactoring, you should put unit tests around the legacy code. That allows you to be sure your refactoring didn't change what the original code did (only how it did it). So my first question is this: how do I unit-test a method in legacy code? How can I put a unit test around a 500 line (if I'm lucky) method that doesn't do just one task? It seems to me that I would have to refactor my legacy code just to make it unit-testable. Does anyone have any experience refactoring using unit tests? And, if so, do you have any practical examples you can share with me? My second question is somewhat hard to explain. Here's an example: I want to refactor a legacy method that populates an object from a database record. Wouldn't I have to write a unit test that compares an object retrieved using the old method, with an object retrieved using my refactored method? Otherwise, how would I know that my refactored method produces the same results as the old method? If that is true, then how long do I leave the old deprecated method in the source code? Do I just whack it after I test a few different records? Or, do I need to keep it around for a while in case I encounter a bug in my refactored code? Lastly, since a couple people have asked...the legacy code was originally written in VB6 and then ported to VB.NET with minimal architecture changes.

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• Unit tests - The benefit from unit tests with contract changes?

  - by Stefan Hendriks

  Recently I had an interesting discussion with a colleague about unit tests. We where discussing when maintaining unit tests became less productive, when your contracts change. Perhaps anyone can enlight me how to approach this problem. Let me elaborate: So lets say there is a class which does some nifty calculations. The contract says that it should calculate a number, or it returns -1 when it fails for some reason. I have contract tests who test that. And in all my other tests I stub this nifty calculator thingy. So now I change the contract, whenever it cannot calculate it will throw a CannotCalculateException. My contract tests will fail, and I will fix them accordingly. But, all my mocked/stubbed objects will still use the old contract rules. These tests will succeed, while they should not! The question that rises, is that with this faith in unit testing, how much faith can be placed in such changes... The unit tests succeed, but bugs will occur when testing the application. The tests using this calculator will need to be fixed, which costs time and may even be stubbed/mocked a lot of times... How do you think about this case? I never thought about it thourougly. In my opinion, these changes to unit tests would be acceptable. If I do not use unit tests, I would also see such bugs arise within test phase (by testers). Yet I am not confident enough to point out what will cost more time (or less). Any thoughts?

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• Unit testing a method with many possible outcomes

  - by Cthulhu

  I've built a simple~ish method that constructs an URL out of approximately 5 parts: base address, port, path, 'action', and a set of parameters. Out of these, only the address part is mandatory, the other parts are all optional. A valid URL has to come out of the method for each permutation of input parameters, such as: address address port address port path address path address action address path action address port action address port path action address action params address path action params address port action params address port path action params andsoforth. The basic approach for this is to write one unit test for each of these possible outcomes, each unit test passing the address and any of the optional parameters to the method, and testing the outcome against the expected output. However, I wonder, is there a Better (tm) way to handle a case like this? Are there any (good) unit test patterns for this? (rant) I only now realize that I've learned to write unit tests a few years ago, but never really (feel like) I've advanced in the area, and that every unit test is a repeat of building parameters, expected outcome, filling mock objects, calling a method and testing the outcome against the expected outcome. I'm pretty sure this is the way to go in unit testing, but it gets kinda tedious, yanno. Advice on that matter is always welcome. (/rant) (note) christmas weekend approaching, probably won't reply to suggestions until next week. (/note)

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