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• Should I bundle C libraries with my Python application?

  - by oceanhug

  If I have a Python package that depends on some C libraries (like say the Gnu Scientific Library (GSL) for numerical computations), is it a good idea to bundle the library with my code? I'd like to make my package as easy to install as possible for users and I don't want them to have to download C libraries by hand and supply include-paths. Also I could always ensure that the version of the library that I ship is compatible with my code. However, is it possible that there are clashes if the user has the library installed already, or ar there any other reasons why I shouldn't do this? I know that I can make it easier for users by just providing a binary distribution, but I'd like to avoid having to maintain binary distributions for all possible OSs. So, I'd like to stick to a source distribution, but for the user (who proudly owns a C compiler) installation should be as easy as python setup.py install.

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• mmap only needed pages of kernel buffer to user space

  - by axeoth

  See also this answer: http://stackoverflow.com/a/10770582/1284631 I need something similar, but without having to allocate a buffer: the buffer is large, in theory, but the user space program only needs to access some parts of it (it mocks some registers of a hardware). As I cannot allocate with vmalloc_user() such a large buffer (kernel 32 bit, in embedded environment, no swap...), I followed the same approach as in the quoted answer, trying to allocate only those pages that are really requested by the user space. So: I use a my_mmap() function for the device file (actually, is the .mmap field of a struct uio_info) to set up the fields of the vma, then, in the vm_area_struct's .fault field (also named my_fault()), I should return a page. except that: In the my_fault() method of vm_area_struct, I cannot obtain a page through: vmf->page=vmalloc_to_page(my_buf + (vmf->pgoff << PAGE_SHIFT)); since there is no allocated buffer: my_buf = vmalloc_user(MY_BUF_SIZE); fails with "allocation failed: out of vmalloc space - use vmalloc= to increase size." (and there is no room or swap to increase that vmalloc= parameter). So, I would need to get a page from the kernel and fill the vmf->page field. How to allocate a page (I assume that the offset of the page is known, as it is vm->pgoff). What base memory should I use instead of my_buf? PS: I also did set up the vma->flags |= VM_NORESERVE; (in the my_mmap()), but not sure if it helps. Is there any vmalloc_user_unreserved()-like function? (let's say, lazy allocation) Also, writing 1 to /proc/sys/vm/overcommit_memory and large values (eg 500) to /proc/sys/vm/overcommit_ratio before trying to my_buf=vmalloc_user(<large_size>) didn't work.

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• Has anyone been successful at a assembler based led blinker for an xcore?

  - by dwelch

  I am liking the http://www.xmos.com chips but want to get a lower level understanding of what is going on. Basically assembler. I am trying to sort out something as simple as an led blinker, set the led, count to N clear the led, count to N, loop forever. Sure I can disassemble a 10 line XC program, but if you have tried that you will see there is a lot of bloat in there that is in every program, what bits are to support the compiler output and what bits are actually setting up the gpio?

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• Best way to get a random number from 1 to 50 which ISN'T x

  - by Cocorico

  Hi guys! So this is probably programming 101 stuff, but I have a problem: I have 2 numbers which are between 0 and 49. Let's call them x and y. Now I want to get a couple of other numbers which are not x or y, but are also between 0 and 49 (I am using Objective C but this is more of a general theory question I think?). Method I thought of is: int a; int b; int c; do { a = arc4random() % 49; } while ((a == x) || (a == y)); do { b = arc4random() % 49; } while ((b == x) || (b == y) || (b == a)); do { c = arc4random() % 49; } while ((c == x) || (c == y) || (c == a) || (c == b)); But it seem kind of bad to me, I don't know, I am just trying to learn to be a better programmer, what would be the most elegant sweet way to do this for best practices? Thanks!

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• Beginner assembly programming memory usage question

  - by Daniel

  I've been getting into some assembly lately and its fun as it challenges everything i have learned. I was wondering if i could ask a few questions When running an executable, does the entire executable get loaded into memory? From a bit of fiddling i've found that constants aren't really constants? Is it just a compiler thing? const int i = 5; _asm { mov i, 0 } // i is now 0 and compiles fine So are all variables assigned with a constant value embedded into the file as well? Meaning: int a = 1; const int b = 2; void something() { const int c = 3; int d = 4; } Will i find all of these variables embedded in the file (in a hex editor or something)? If the executable is loaded into memory then "constants" are technically using memory? I've read around on the net people saying that constants don't use memory, is this true?

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• Visual Studio 2008 awful performance

  - by Nima

  Hi, I have ported a piece of C++ code, that works out of core, from Linux(Ubuntu) to Windows(Vista) and I realized that it works about 50times slower on VS2008! I removed all the out of core parts and now I just have a piece of code that has nothing to do with the hard disk. I set compiler parameters to O2 in Project Properties but still get about 10times slower than g++ in linux! Does anybody have an idea why it is this much slower under VS? I really appreciate any kind of hint! Thanks,

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• Compile-time trigonometry in C

  - by lhahne

  I currently have code that looks like while (very_long_loop) { ... y1 = getSomeValue(); ... x1 = y1*cos(PI/2); x2 = y2*cos(SOME_CONSTANT); ... outputValues(x1, x2, ...); } the obvious optimization would be to compute the cosines ahead-of-time. I could do this by filling an array with the values but I was wondering would it be possible to make the compiler compute these at compile-time?

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• Passing a template func. as a func. ptr to an overloaded func. - is there a way to compile this code

  - by LoudNPossiblyRight

  Just a general c++ curiosity: This code below shouldn't compile because it's impossible to know which to instantiate: temp(const int&) or temp(const string&) when calling func(temp) - this part i know. What i would like to know is if there is anything i can do to the line marked PASSINGLINE to get the compiler to deduce that i want FPTR1 called and not FPTR2 ? #include<iostream> using std::cout; using std::endl; /*FPTR1*/ void func(void(*fptr)(const int&)){ fptr(1001001);} /*FPTR2*/ void func(void(*fptr)(const string&)){ fptr("1001001"); } template <typename T> void temp(const T &t){ cout << t << endl; } int main(){ /*PASSINGLINE*/ func(temp); return 0; } Thank you.

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• Custom class object in Initialization list

  - by Michael

  I have a class Bar: class Bar { public: Bar(void); ~Bar(void); }; And a class Foo that gets a reference to Bar object as a constructor parameter and needs to save it in a private member bar_ : class Foo { private: Bar& bar_; public: Foo(Bar& bar) : bar_(bar) {} ~Foo(void) {} }; This doesn't compile : overloaded member function not found in 'Parser' missing type specifier - int assumed. Note: C++ does not support default-int Now i suspect couple of things that i need to assure, the second error is for Bar& bar_; declaration in Foo. Do i need to use an explicit constructor when declaring bar_ ? I am interested in learning how the compiler works regarding this matter, so a detailed explanation would be highly appreciated. Thanks.

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• Standard (cross-platform) way for bit manipulation

  - by Kiril Kirov

  As are are different binary representation of the numbers (for example, take big/little endian), is this cross-platform: some_unsigned_type variable = some_number; // set n-th bit, starting from 1, // right-to-left (least significant-to most significant) variable |= ( 1 << ( n - 1 ) ); // clear the same bit: variable &= ~( 1 << ( n - 1 ) ); In other words, does the compiler always take care of the different binary representation of the unsigned numbers, or it's platform-specific? And what if variable is signed integral type (for example, int) and its value is zero positive negative? What does the Standard say about this? P.S. And, yes, I'm interesting in both - C and C++, please don't tell me they are different languages, because I know this :) I can paste real example, if needed, but the post will become too long

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• Can i have a negative value as constant expression in Scala?

  - by Klinke

  I have an Java-Annotation that return a double value: @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.FIELD) public @interface DoubleValue { double value(); } When i try to attach the annotation to a field in a scala class and the value is negativ like here: class Test { @DoubleValue(-0.05) var a = _ } i get an compiler error with the message: "annotation argument needs to be a constant; found: 0.05.unary_-". I understood that i need a numerical literal and i looked into the Scala Language Specification and it seems, that the - sign is only used for the exponent but not for the mantissa. Does someone has an idea how i can have a negative value as runtime information using annotations? Thanks, Klinke

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• Declaring a prototype of type "struct" - C

  - by Jamie Keeling

  I've been racking my brains on this for a while, I'm simply trying to create a method that returns a struct as I wish to return two int's. My prototype for the method is as follows: typedef struct RollDice(); Also the method itself: typedef struct RollDice() { diceData diceRoll; diceRoll.dice1 = 0; diceRoll.dice2 = 0; return diceRoll; } The compiler shows the error: "Syntax error: ')'" for both the prototype and actual method. The struct itself: typedef struct { int dice1; int dice2; }diceData; Is it obvious where I'm going wrong? I've tried everything I can think of. Thanks

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• How to free memory in try-catch blocks?

  - by Kra

  Hi, I have a simple question hopefully - how does one free memory which was allocated in the try block when the exception occurs? Consider the following code: try { char *heap = new char [50]; //let exception occur here delete[] heap; } catch (...) { cout << "Error, leaving function now"; //delete[] heap; doesn't work of course, heap is unknown to compiler return 1; } How can I free memory after the heap was allocated and exception occurred before calling delete[] heap? Is there a rule not to allocate memory on heap in these try .. catch blocks? Thanks

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• Parenthesis operator in C. What is the effect in the following code

  - by Andre

  Hi everyone, I was playing with a macro to enable/disable traces when I came out with the following code when the macro is disabled: int main { ("Hello world"); } This code is valid and I got the desired effect (nothing happens when the macro is disabled) but I couldn't figure out what exactly is happening. Is the compiler seeing the parenthesis as a "nameless" method declaration? To make it clearer the code is : #ifdef TRACE #define trace printf("%s %d -> ",__FILE__, __LINE__);printf else #define trace #endif int main { trace("Hello world"); } Thanks in advance.

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• Jquery number of clicks record

  - by Maxime

  Hi, I am working on this page where I'm using a Jquery Mp3 Player (Jplayer) with its playlist. What I want to do is very simple in theory: I want to record the number of clicks for every playlist element. When someone enters the page, his number of clicks are at 0 for every element. The visitor can click a few times on element #1, then go to element #2 (which will be at 0), then come back to element #1 and the number of clicks must be saved. We don't need to save it for next visits. Jplayer has this function that loads each time a new playlist element is being loaded: function playListChange( index ) In which every element has its own ID dynamically updated: myPlayList[index].song_id Here's my code: function playListChange( index ) { var id = myPlayList[index].song_id; if(!o) { var o = {}; } if(!o[id]) { o[id] = 0; } alert(o[id]); … $("#mydiv").click { o[id] = o[id]+1; } … But o[id] is reset every time and the alert always show 0. Why? Thanks for any reply.

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• Does Msbuild recognise any build configurations other than DEBUG|RELEASE

  - by Dean

  I created a configuration named Test via Visual Studio which currently just takes all of DEBUG settings, however I employ compiler conditions to determine some specific actions if the build happens to be TEST|DEBUG|RELEASE. However how can I get my MSBUILD script to detect the TEST configuration?? Currently I build <MSBuild Projects="@(SolutionsToBuild)" Properties="Configuration=$(Configuration);OutDir=$(BuildDir)\Builds\" /> Where @(SolutionsToBuild) is a my solution. In the Common MsBuild Project Properties it states that $(Configuration) is a common property but it always appears blank? Does this mean that it never gets set but is simply reserved for my use or that it can ONLY detect DEBUG|RELEASE. If so what is the point in allowing the creation of different build configurations?

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• error handling strategies in C?

  - by Leo

  Given the code below: typedef struct {int a;} test_t; arbitrary_t test_dosomething(test_t* test) { if (test == NULL) { //options: //1. print an error and let it crash //e.g. fprintf(stderr, "null ref at %s:%u", __FILE__, __LINE__); //2. stop the world //e.g. exit(1); //3. return (i.e. function does nothing) //4. attempt to re-init test } printf("%d", test->a); //do something w/ test } I want to get a compiler error if test is ever NULL, but I guess that's not possible in C. Since I need to do null checking at runtime, what option is the most proper way to handle it?

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• xml to xsd to c# class - C# 3.0, .net 3.5

  - by uno

  Following this articlelink text one of the comments from 'zanoni' said he did it this way Using .NET 3.5: [XmlRoot] public class EmailConfiguration { [XmlElement] public string DataBoxID { get; set; } [XmlElement] public DefaultSendToAddressCollectionClass DefaultSendToAddressCollection { get; set; } } public class DefaultSendToAddressCollectionClass { [XmlElement] public string[] EmailAddress { get; set; } } How would I get my class to be as what he described? I ran the xsd tool and it is in the fashion as what shane posted in the above link [System.CodeDom.Compiler.GeneratedCodeAttribute("xsd", "2.0.50727.3038")] [System.SerializableAttribute()] [System.Diagnostics.DebuggerStepThroughAttribute()] [System.ComponentModel.DesignerCategoryAttribute("code")] [System.Xml.Serialization.XmlTypeAttribute(AnonymousType=true)] [System.Xml.Serialization.XmlRootAttribute(Namespace="", IsNullable=false)] public partial class EmailConfiguration : object, System.ComponentModel.INotifyPropertyChanged { private string dataBoxIDField; private EmailConfigurationDefaultSendToAddressCollection[] defaultSendToAddressCollectionField; /// <remarks/> [System.Xml.Serialization.XmlElementAttribute(Form=System.Xml.Schema.XmlSchemaForm.Unqualified)] public string DataBoxID { get { return this.dataBoxIDField; } set { this.dataBoxIDField = value; this.RaisePropertyChanged("DataBoxID"); } }

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• Explicit initialization of struct/class members

  - by Zephon

  struct some_struct{ int a; }; some_struct n = {}; n.a will be 0 after this; I know this braces form of initialization is inherited from C and is supported for compatibility with C programs, but this only compiles with C++, not with the C compiler. I'm using Visual C++ 2005. In C this type of initialization struct some_struct n = {0}; is correct and will zero-initialize all members of a structure. Is the empty pair of braces form of initialization standard? I first saw this form of initialization in a WinAPI tutorial from msdn.

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• Void in main and keeping Dos program from dying

  - by TimothyTech

  Alright, so im using bloodshed complier, first thing i should note is im using a 2001 edition C++ for the aboslute beginner, was there any changes to C++ since 2001 that would effect the validity of this book? i ask because i know php has php5 and now php6 but i havent seen any C++3. now for the reason i asked that, in this code it uses, void main (void) why would i want an arguement to be void? what does this do. But when i run the " void main (void) in my compiler it says that main must have a "int" before it. so i cant have "void" main (void); also, once the code runs through, as long as there isnt a "cin" the program closes. is this normal behavior, is there a better way to stop this besides making a cin at the end of my program.

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• Key Value Observation (ala Cocoa) in GWT ?

  - by user179997

  Hi all, There are these 2 frameworks out there in the same "cloud application" space as GWT: Sproutcore and Cappuccino. Cappuccino is Cocoa for the web, Sproutcore is Cocoa-like and one very central idea in both is Key Value Observation where the framework itself provides the glue to change all dependencies of an object when it changes, and you only have to declare those dependencies. If that was too poorly expressed please see this presentation: http://www.infoq.com/presentations/subelsky-sproutcore-intro Since the pattern reduces the amount of code you type it reduces the number of bugs. Maybe it's too much to ask but I would like to have that and all the benefits of Eclipse/compiler that come with GWT. Is there support for this in GWT, or a library already developed? Or maybe there is support in some of the component libraries for GWT out there? Thanks

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• how VAR is determined against many options?

  - by Royi Namir

  i have this code : IEnumerable<string> q = customers /*EF entity*/ .Select (c => c.Name.ToUpper()) .OrderBy (n => n) To select entity, ObjectContext actually create ObjectQuery, which implement IQueryable. The object return from ObjectQuery, is not normal object, but EntityObject but what if i write : ( notice the var) var q = customers /*EF entity*/ .Select (c => c.Name.ToUpper()) .OrderBy (n => n) it can be determined both to ienumerable or iqueryable : because ObjectQuery Also implements IEnumerable... i dont know if there's any specific info which tell the compiler "use A and not B. A is more specific..." ( there must be...i just cant find it) any help ? how will it know to use A || B ?

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• why make said no rule to make target

  - by guilin ??

  Isn't Makefile syntax is target: require_files cmd... Why I got this problem? Makefile MXMLC = /opt/flex/bin/mxmlc MXMLC_RELEASE = $(MXMLC) -debug=false -compiler.optimize=true release: bin-release/Wrapper.swf, bin-release/Application.swf bin-release/Application.swf: src/**/*.as, lib/*.swc $(MXMLC_RELEASE) -output bin-release/Application.swf src/Application.as @@-rm ../server/public/game/Application.swf $(CP) bin-release/Application.swf ../server/public/game/Application.swf bin-release/Wrapper.swf: src/*.as, src/engine/**/*.as, lib/*.swc $(MXMLC_RELEASE) -output bin-release/Wrapper.swf src/Wrapper.as @@-rm ../server/public/game/Wrapper.swf $(CP) bin-release/Wrapper.swf ../server/public/game/Wrapper.swf $: make bin-release/Application.swf ~/workspace/project/src/flash [2]19:20 make: * No rule to make target src/constant/*.as,', needed bybin-release/Application.swf'. Stop.

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• Why won't the debugger update?

  - by Tanner

  Hello everyone, Ive had this problem multiple times and it ruins my projects, I make some changes, like say I have a button in the top left corner of the form and move it to the top right corner, then I press debug but nothing happens to the form, it doesn't change the button is still in the top left-hand corner instead of the top right, and it also doesn't except any new code, its like it saved the project right there and won't move on. Does any one know why or had this problem before? Please, Help!!!! Additional Details: Compiler: Microsoft Visual C# 2008 Express Edition I once fixed this problem by rebuilding the solution, but its never worked again.

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• Why do Java source files go into a directory structure?

  - by bdhar

  Suppose that I am creating a Java project with the following classes com.bharani.ClassOne com.bharani.ClassTwo com.bharani.helper.HelperOne com.bharani.helper.support.HelperTwo with files put immediately under the folder 'src' src/ClassOne.java src/ClassTwo.java src/HelperOne.java src/HelperTwo.java and compile them using the command $ javac src/*.java -d classes (assuming that classes directory exists) The compiler compiles these files and put the class files in appropriate sub-directories inside the 'classes' directory like this classes/com/bharani/ClassOne.class classes/com/bharani/ClassTwo.class classes/com/bharani/helper/HelperOne.class classes/com/bharani/helper/support/HelperTwo.class Because the spec mandates that the classes should go inside appropriate directory structure. Fine. My question is this: When I use an IDE such as Eclipse or NetBeans, they create the directory structure for the source code directory ('src' directory here) also. Why is that? Is it mandatory? Or, is it just a convention? Thanks.

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