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  • Convert any currency string to double

    - by James
    I need to store multiple currencies in SQL server. I understand that SQL won't support all different types of currencies (unless I store it as a string, but I don't want to do that). My idea was to convert all the values from their currency format to a standard double and store that instead. Then just re-format based on the culture info when displaying. However, I have tried doing something like e.g. var cultureInfo = new System.Globalization.CultureInfo("en-US"); double plain = return Double.Parse("$20,000.00", cultureInfo); This doesn't ever seem to work it always throws a FormatException. Even removing the currency symbol and just trying to do this based on the number alone does the same thing. This is just an example I want to support pretty much any type of currency. Is there a standard way of stripping out currency and getting the value as a double?

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  • What's your preferred pointer declaration style, and why?

    - by Owen
    I know this is about as bad as it gets for "religious" issues, as Jeff calls them. But I want to know why the people who disagree with me on this do so, and hear their justification for their horrific style. I googled for a while and couldn't find a style guide talking about this. So here's how I feel pointers (and references) should be declared: int* pointer = NULL; int& ref = *pointer; int*& pointer_ref = pointer; The asterisk or ampersand goes with the type, because it modifies the type of the variable being declared. EDIT: I hate to keep repeating the word, but when I say it modifies the type I'm speaking semantically. "int* something;" would translate into English as something like "I declare something, which is a pointer to an integer." The "pointer" goes along with the "integer" much more so than it does with the "something." In contrast, the other uses of the ampersand and asterisk, as address-of and dereferencing operators, act on a variable. Here are the other two styles (maybe there are more but I really hope not): int *ugly_but_common; int * uglier_but_fortunately_less_common; Why? Really, why? I can never think of a case where the second is appropriate, and the first only suitable perhaps with something like: int *hag, *beast; But come now... multiple variable declarations on one line is kind of ugly form in itself already.

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  • Float addition promoted to double?

    - by Andreas Brinck
    I had a small WTF moment this morning. Ths WTF can be summarized with this: float x = 0.2f; float y = 0.1f; float z = x + y; assert(z == x + y); //This assert is triggered! (Atleast with visual studio 2008) The reason seems to be that the expression x + y is promoted to double and compared with the truncated version in z. (If i change z to double the assert isn't triggered). I can see that for precision reasons it would make sense to perform all floating point arithmetics in double precision before converting the result to single precision. I found the following paragraph in the standard (which I guess I sort of already knew, but not in this context): 4.6.1. "An rvalue of type float can be converted to an rvalue of type double. The value is unchanged" My question is, is x + y guaranteed to be promoted to double or is at the compiler's discretion? UPDATE: Since many people has claimed that one shouldn't use == for floating point, I just wanted to state that in the specific case I'm working with, an exact comparison is justified. Floating point comparision is tricky, here's an interesting link on the subject which I think hasn't been mentioned.

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  • floor of double(time_t)

    - by plok
    I cannot understand why this throws undefined reference to `floor'": double curr_time = (double)time(NULL); return floor(curr_time); Hasn't it been casted to double, which is what floor receives?

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  • Double pointer const-correctness warnings in C

    - by Michael Koval
    You can obviously cast a pointer to non-const data to a a pointer of the same type to const data: int *x = NULL; int const *y = x; Adding additional const qualifiers to match the additional indirection should logically work the same way: int * *x = NULL; int *const *y = x; /* okay */ int const *const *z = y; /* warning */ Compiling this with GCC or Clang with the -Wall flag, however, results in the following warning: test.c:4:23: warning: initializing 'int const *const *' with an expression of type 'int *const *' discards qualifiers in nested pointer types int const *const *z = y; /* warning */ ^ ~ Why does adding an additional const qualifier "discard qualifiers in nested pointer types"?

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  • Why implement DB connection pointer object as a reference counting pointer? (C++)

    - by DVK
    At our company one of the core C++ classes (Database connection pointer) is implemented as a reference counting pointer. To be clear, the objects are NOT DB connections themselves, but pointers to a DB connection object. The library is very old, and nobody who designed is around anymore. So far, nether I, nor any C++ experts in the company that I asked have come up with a good reason for why this particular design was chosen. Any ideas? It is introducing some problems (partially due to awful reference pointer implementation used), and I'm trying to understand if this design actually has some deep underlying reasons? The usage pattern these days seems to be that the DB connection pointer object is returned by a DB connection manager class, and it's somewhat unclear whether DB connection pointers were designed to be able to be used independently of DB connection manager.

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  • system out output for double numbers in a java program

    - by Nikunj Chauhan
    I have a program where I am generating two double numbers by adding several input prices from a file based on a condition. String str; double one = 0.00; double two = 0.00; BufferedReader in = new BufferedReader(new FileReader(myFile)); while((str = in.readLine()) != null){ if(str.charAt(21) == '1'){ one += Double.parseDouble(str.substring(38, 49) + "." + str.substring(49, 51)); } else{ two += Double.parseDouble(str.substring(38, 49) + "." + str.substring(49, 51)); } } in.close(); System.out.println("One: " + one); System.out.println("Two: " + two); The output is like: One: 2773554.02 Two: 6.302505836000001E7 Question: None of the input have more then two decimals in them. The way one and two are getting calculated exactly same. Then why the output format is like this. What I am expecting is: One: 2773554.02 Two: 63025058.36 Why the printing is in two different formats ? I want to write the outputs again to a file and thus there must be only two digits after decimal.

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  • Double paging definition

    - by Albinoswordfish
    This is not a programming question but more of an operating system question Right now I'm trying to learn what exactly Double paging means. I see two different terms, double paging on disk and double paging in memory. Apparently this problem arises when we introduce a buffer cache to store disk blocks when doing File I/O But I'm not really sure what exactly this term means. If anybody could specify it would be very helpful.

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  • What does it mean to double license?

    - by Adrian Panasiuk
    What does it mean to double license code? I can't just put both licenses in the source files. That would mean that I mandate users to follow the rules of both of them, but the licenses will probably be contradictory (otherwise there'd be no reason to double license). I guess this is something like in cryptographic chaining, cipher = crypt_2(crypt_1(clear)) (generally) means, that cipher is neither the output of crypt_2 on clear nor the output of crypt_1 on clear. It's the output of the composition. Likewise, in double-licensing, in reality my code has one license, it's just that this new license says please follow all of the rules of license1, or all of the rules of license2, and you are hereby granted the right to redistribute this application under this "double" license, license1 or license2, or any license under which license1 or license2 allow you to redistribute this software, in which case you shall replace the relevant licensing information in this application with that of the new license. (Does this mean that before someone may use the app under license1, he has to perform the operation of redistributing to self? How would he document the fact that he did that operation?) Am I correct. What LICENSE file and what text to put in the source files would I need if I wanted to double license on, for the sake of example, Apachev2 and GPLv3 ?

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  • Memory leaks while using array of double

    - by Gacek
    I have a part of code that operates on large arrays of double (containing about 6000 elements at least) and executes several hundred times (usually 800) . When I use standard loop, like that: double[] singleRow = new double[6000]; int maxI = 800; for(int i=0; i<maxI; i++) { singleRow = someObject.producesOutput(); //... // do something with singleRow // ... } The memory usage rises for about 40MB (from 40MB at the beggining of the loop, to the 80MB at the end). When I force to use the garbage collector to execute at every iteration, the memory usage stays at the level of 40MB (the rise is unsignificant). double[] singleRow = new double[6000]; int maxI = 800; for(int i=0; i<maxI; i++) { singleRow = someObject.producesOutput(); //... // do something with singleRow // ... GC.Collect() } But the execution time is 3 times longer! (it is crucial) How can I force the C# to use the same area of memory instead of allocating new ones? Note: I have the access to the code of someObject class, so if it would be needed, I can change it.

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  • LLVM: Passing a pointer to a struct, which holds a pointer to a function, to a JIT function

    - by Rusky
    I have an LLVM (version 2.7) module with a function that takes a pointer to a struct. That struct contains a function pointer to a C++ function. The module function is going to be JIT-compiled, and I need to build that struct in C++ using the LLVM API. I can't seem get the pointer to the function as an LLVM value, let alone pass a pointer to the ConstantStruct that I can't build. I'm not sure if I'm even on the track, but this is what I have so far: void print(char*); vector<Constant*> functions; functions.push_back(ConstantExpr::getIntToPtr( ConstantInt::get(Type::getInt32Ty(context), (int)print), /* function pointer type here, FunctionType::get(...) doesn't seem to work */ )); ConstantStruct* struct = cast<ConstantStruct>(ConstantStruct::get( cast<StructType>(m->getTypeByName("printer")), functions )); Function* main = m->getFunction("main"); vector<GenericValue> args; args[0].PointerVal = /* not sure what goes here */ ee->runFunction(main, args);

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  • Java code optimization leads to numerical inaccuracies and errors

    - by rano
    I'm trying to implement a version of the Fuzzy C-Means algorithm in Java and I'm trying to do some optimization by computing just once everything that can be computed just once. This is an iterative algorithm and regarding the updating of a matrix, the clusters x pixels membership matrix U, this is the update rule I want to optimize: where the x are the element of a matrix X (pixels x features) and v belongs to the matrix V (clusters x features). And m is a parameter that ranges from 1.1 to infinity. The distance used is the euclidean norm. If I had to implement this formula in a banal way I'd do: for(int i = 0; i < X.length; i++) { int count = 0; for(int j = 0; j < V.length; j++) { double num = D[i][j]; double sumTerms = 0; for(int k = 0; k < V.length; k++) { double thisDistance = D[i][k]; sumTerms += Math.pow(num / thisDistance, (1.0 / (m - 1.0))); } U[i][j] = (float) (1f / sumTerms); } } In this way some optimization is already done, I precomputed all the possible squared distances between X and V and stored them in a matrix D but that is not enough, since I'm cycling througn the elements of V two times resulting in two nested loops. Looking at the formula the numerator of the fraction is independent of the sum so I can compute numerator and denominator independently and the denominator can be computed just once for each pixel. So I came to a solution like this: int nClusters = V.length; double exp = (1.0 / (m - 1.0)); for(int i = 0; i < X.length; i++) { int count = 0; for(int j = 0; j < nClusters; j++) { double distance = D[i][j]; double denominator = D[i][nClusters]; double numerator = Math.pow(distance, exp); U[i][j] = (float) (1f / (numerator * denominator)); } } Where I precomputed the denominator into an additional column of the matrix D while I was computing the distances: for (int i = 0; i < X.length; i++) { for (int j = 0; j < V.length; j++) { double sum = 0; for (int k = 0; k < nDims; k++) { final double d = X[i][k] - V[j][k]; sum += d * d; } D[i][j] = sum; D[i][B.length] += Math.pow(1 / D[i][j], exp); } } By doing so I encounter numerical differences between the 'banal' computation and the second one that leads to different numerical value in U (not in the first iterates but soon enough). I guess that the problem is that exponentiate very small numbers to high values (the elements of U can range from 0.0 to 1.0 and exp , for m = 1.1, is 10) leads to ver y small values, whereas by dividing the numerator and the denominator and THEN exponentiating the result seems to be better numerically. The problem is it involves much more operations. Am I doing something wrong? Is there a possible solution to get both the code optimized and numerically stable? Any suggestion or criticism will be appreciated.

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  • Double multiplied by 100 and then cast to long is giving wrong value

    - by xyz
    I have the following code: Double i=17.31; long j=(long) (i*100); System.out.println(j); O/P : 1730 //Expected:1731 Double i=17.33; long j=(long) (i*100); System.out.println(j); O/P : 1732 //Expected:1733 Double i=17.32; long j=(long) (i*100); System.out.println(j); O/P : 1732 //Expected:1732{As expected} Double i=15.33; long j=(long) (i*100); System.out.println(j); O/P : 1533 //Expected:1533{as Expected} I have tried to Google but unable to find reason.I am sorry if the question is trivial.

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  • How to assign a value to an pointer-pointer passed in call by reference?

    - by mystify
    I want to achieve something similar to what these guys do here: - (NSUInteger)countForFetchRequest:(NSFetchRequest *)request error:(NSError **)error like you can see, you pass an NSError pointer and that nice method will assign a real NSError object to your pointer in case there is an error. So the cool thing about this is, that the method returns an NSUInteger but can ALSO return an NSError, without having to mess around with ugly and fat arrays or dictionaries. So how could I assign an object to the passed-in error pointer?

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  • Initializing and accessing a pointer from an array of pointers

    - by idealistikz
    Suppose I have the following: void **Init(int numElems) { //What is the best way to intialize 'ptrElems' to store an array of void *'s? void **ptrElems = malloc(numElems * sizeof(void *)); return ptrElems; } //What is the best way to return a pointer pointing at the index passed as a parameter? void **GetPtr(void **ptrElems, int index) { void **elem = elems + (index * sizeof(void *)); return elem; } First, what is the best way to intialize 'ptrElems' to store an array of pointers? I use malloc because assigning it to an array will not persist after the end of the function. Second, what is the best way to point to the pointer at the specified index? I tried typecasting the first line of the 'GetPtr' function to ensure proper pointer arithmetic, but I receive the warning, 'initialization from incompatible pointer type'. Is it necessary to typecast?

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  • Detect double-tap on UISlider?

    - by Randy
    I can detect single/double-taps in specific views with: NSSet *myTouches = [event touchesForView:mySpecificView.view]; but I want to detect a double-tap on the button of a slider and can't find any reference to it. Is there a replacement for "touchesForView:" where I can enter the name of my slider? usage: I have three sliders with their default value being directly in the center of the slider. Once the position of the slider has changed, I want a quick way to individually reset each slider to its default position. I currently have each slider's containing view set to respond to a double-tap, updating each slider. It works fine, but doesn't seem natural. ie.I can't double-tap on the slider itself because the slider intercepts the taps and doesn't pass them on to the surrounding view. thanks in advance

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  • How do you delete a pointer without deleting the data the pointer points to?

    - by Faken
    I have a pointer that points to an array and another pointer referencing the same array. How do i delete any one of those pointers without killing the array such that the second undeleted pointer still works? for example: int* pointer1 = new int [1000]; int* pointer2; pointer2 = pointer1; Now i want to get rid of pointer1, how would i do it such that i can continue to access the array normaly through pointer2?

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  • Determining if Memory Pointer is Valid - C++

    - by Jim Fell
    It has been my observation that if free( ptr ) is called where ptr is not a valid pointer to system-allocated memory, an access violation occurs. Let's say that I call free like this: LPVOID ptr = (LPVOID)0x12345678; free( ptr ); This will most definitely cause an access violation. Is there a way to test that the memory location pointed to by ptr is valid system-allocated memory? It seems to me that the the memory management part of the Windows OS kernel must know what memory has been allocated and what memory remains for allocation. Otherwise, how could it know if enough memory remains to satisfy a given request? (rhetorical) That said, it seems reasonable to conclude that there must be a function (or set of functions) that would allow a user to determine if a pointer is valid system-allocated memory. Perhaps Microsoft has not made these functions public. If Microsoft has not provided such an API, I can only presume that it was for an intentional and specific reason. Would providing such a hook into the system prose a significant threat to system security? Situation Report Although knowing whether a memory pointer is valid could be useful in many scenarios, this is my particular situation: I am writing a driver for a new piece of hardware that is to replace an existing piece of hardware that connects to the PC via USB. My mandate is to write the new driver such that calls to the existing API for the current driver will continue to work in the PC applications in which it is used. Thus the only required changes to existing applications is to load the appropriate driver DLL(s) at startup. The problem here is that the existing driver uses a callback to send received serial messages to the application; a pointer to allocated memory containing the message is passed from the driver to the application via the callback. It is then the responsibility of the application to call another driver API to free the memory by passing back the same pointer from the application to the driver. In this scenario the second API has no way to determine if the application has actually passed back a pointer to valid memory.

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  • Detect pointer arithmetics because of LARGEADDRESSAWARE

    - by Suma
    I would like to switch my application to LARGEADDRESSAWARE. One of issues to watch for is pointer arithmetic, as pointer difference can no longer be represented as signed 32b. Is there some way how to find automatically all instances of pointer subtraction in a large C++ project? If not, is there some "least effort" manual or semi-automatic method how to achieve this?

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  • ILNumerics multiply complex with matrix<double>

    - by nik
    I m looking at ILNumerics to translate some matlab code into c#. How would I multiply a complex and a double? Simplified description: In Matlab: A=[1 2 3] i*A*A' Returns a complex number. How would I do the same in ILNumerics: ILArray<double> A = ILMath.array(1.0, 2.0, 3.0); complex B = complex.i * ILMath.multiply(A,A.T); Throws the error: Operator '*' cannot be applied to operands of type 'ILNumerics.complex' and 'ILNumerics.ILRetArray<double>' Update This works: double C = 14.0; complex D = complex.i * C; But shouldnt: ILMath.multiply(A,A.T) also return 14.0?

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  • boost::function function pointer to parameters?

    - by high6
    How does boost::function take a function pointer and get parameters from it? I want wrap a function pointer so that it can be validated before being called. And it would be nice to be able to call it like boost::function is with the () operator and not having to access the function pointer member. Wrapper func; func(5); //Yes :D func.Ptr(5) //Easy to do, but not as nice looking

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