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• C++0x, How do I expand a tuple into variadic template function arguments?

  - by Gustaf

  Consider the case of a templated function with variadic template arguments: template<typename Tret, typename... T> Tret func(const T&... t); Now, I have a tuple t of values. How do I call func() using the tuple values as arguments? I've read about the bind() function object, with call() function, and also the apply() function in different some now-obsolete documents. The GNU GCC 4.4 implementation seems to have a call() function in the bind() class, but there is very little documentation on the subject. Some people suggest hand-written recursive hacks, but the true value of variadic template arguments is to be able to use them in cases like above. Does anyone have a solution to is, or hint on where to read about it?

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• Tkinter after that survives clock rewinding.

  - by Oren

  I noticed that in my version of Tkinter, the after() call does not survive system clock rewinding. If the after(x, func) was called, and the system clock was rewinded, func will be called only after the clock returned to its time before the rewind + x milliseconds. I assume this is because Tkinter uses the system-clock instead of the "time.clock" (the amount of time that the program is running). I tested it only on windows, and maybe its because I have an old version of Tkinter. I want my App to work on computers that synchronize their clock from the network... Does anyone have a simple solution?

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• How to dynamically use the PropertyType reflection attribute to create a respective typed Function<

  - by vsj

  I want to use type returned by PropertyType to create a typed function. I found this similiar http://stackoverflow.com/questions/914578/using-type-returned-by-type-gettype-in-c but this mentions how to create a list but does not mention how we can create a Func<. Please help me out. Pseudocode: PropertyInfo inf = typeof(SomeClass).GetProperty("PropertyName"); Type T=inf.PropertyType; Expression<Func<SomeClass,T>> le = GetPropertyOrFieldByName<SomeClass, T>("PropertyName");

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• Why is forwarding variadic parameters invalid?

  - by awesomeyi

  Consider the variadic function parameter: func foo(bar:Int...) -> () { } Here foo can accept multiple arguments, eg foo(5,4). I am curious about the type of Int... and its supported operations. For example, why is this invalid? func foo2(bar2:Int...) -> () { foo(bar2); } Gives a error: Could not find an overload for '_conversion' that accepts the supplied arguments Why is forwarding variadic parameters invalid? What is the "conversion" the compiler is complaining about?

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• OpenGLES iPhone Depth Blending problem

  - by user359103

  Hi, I am trying to make an OpenGLES 2.0 cube application. The idea was to have a texture (with an alpha 75%) applied to all 6 faces of the cube. This would mean that even if I rotate the cube i would be able to see all 6 faces at any given frame. Now I have enabled depth test(my app needs this!!) and blending. The Depth func is LEQUAL and blend func is SRC_ALPHA, ONE_MINUS_SRC_ALPHA. Now, the issue is that at some cube faces don't show the underlying faces. I am not able to understand this because the logic works fine with the other cube faces. Just for the record, I have disabled CULL_FACE. Thanks in advance. Regards, Puzzler

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• Query on the scope of local variables in C

  - by darkie15

  All, Consider the following code: void func(void) { int a; printf ("%d", a); } int main(int argc, char **argv) { int a = 3; func(); printf("%d", a); } According to my understanding, the output should be: <junk value><3> Can anyone please confirm my understanding? My basic query is, does the compiler refer to the outer scope for a variable that has been declared but not defined? Regards, darkie

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• parsing Two-dimensional array in c

  - by gitter78

  I'm trying to parse an array that looks like the one below: char *arr[][2] = { { "1", "Purple" }, { "2", "Blue" }, { "22", "Red" }, ... }; I was thinking having a loop as: char *func(char *a){ for(i = 0; i<sizeof(arr)/sizeof(arr[0]);i++){ if(strstr(a,arr[i][0])!=NULL) return arr[i][1]; } } char *out; const char *hello = "this is my 2 string"; out = func(hello); In this case, I'm trying to get the second value based on the first one: Purple, Blue Red, etc.. The question is how would go in parsing this and instead of printing out the value, return the value. UPDATE/FIXED: It has been fixed above. Thanks

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• How to bind to foreach context ?

  - by Rebol Tutorial

  Currently I have this snippet of code: save-blocks: func[file /local f out][ foreach [field1 field2 field3 field4 field5 field6 field7 field8 field9] blocks [ out: copy "" repeat n 9 [ part: get bind to-word rejoin ["field" n] 'field1 out: rejoin [out part ";"] ] remove back tail out write/lines/append f out ] It's not generic enough, I'd like to pass this block: [field1 field2 field3 field4 field5 field6 field7 field8 field9] as parameter and write something like this: save-blocks: func[block file /local f out][ foreach block blocks [ out: copy "" repeat n 9 [ part: get bind to-word rejoin ["field" n] 'field1 out: rejoin [out part ";"] ] remove back tail out write/lines/append f out ] But I don't know how to bind in this case too hard for me :(

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• How do I put a vector inside of a struct in Go?

  - by Brian T Hannan

  I'm trying to put a vector variable inside a struct in Google's Go programming language. This is what I have so far: Want: type Point struct { x, y int } type myStruct struct { myVectorInsideStruct vector; } func main(){ myMyStruct := myStruct{vector.New(0)}; myPoint := Point{2,3}; myMyStruct.myVectorInsideStruct.Push(myPoint); } Have: type Point struct { x, y int } func main(){ myVector := vector.New(0); myPoint := Point{2,3}; myVector.Push(myPoint); } I can get the vector to work in my main function just fine, but I want to encapsulate it inside a struct for easier use.

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• What is the purpose of this delegate usage?

  - by Kev

  Whilst poking around some code in .NET Reflector in an app I don't have the source code for I found this: if (DeleteDisks) { using (List<XenRef<VDI>>.Enumerator enumerator3 = list.GetEnumerator()) { MethodInvoker invoker2 = null; XenRef<VDI> vdiRef; while (enumerator3.MoveNext()) { vdiRef = enumerator3.Current; if (invoker2 == null) { // // Why do this? // invoker2 = delegate { VDI.destroy(session, vdiRef.opaque_ref); }; } bestEffort(ref caught, invoker2); } } } if (caught != null) { throw caught; } private static void bestEffort(ref Exception caught, MethodInvoker func) { try { func(); } catch (Exception exception) { log.Error(exception, exception); if (caught == null) { caught = exception; } } } Why not call VDI.destroy() directly. Is this just a way of wrapping the same pattern of try { do something } catch { log error } if it's used a lot?

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• How to create and Expression tree to do the same as "StartsWith"

  - by Jonathan

  Hi to all. Currently, I have this method to compare two numbers Private Function ETForGreaterThan(ByVal query As IQueryable(Of T), ByVal propertyValue As Object, ByVal propertyInfo As PropertyInfo) As IQueryable(Of T) Dim e As ParameterExpression = Expression.Parameter(GetType(T), "e") Dim m As MemberExpression = Expression.MakeMemberAccess(e, propertyInfo) Dim c As ConstantExpression = Expression.Constant(propertyValue, propertyValue.GetType()) Dim b As BinaryExpression = Expression.GreaterThan(m, c) Dim lambda As Expression(Of Func(Of T, Boolean)) = Expression.Lambda(Of Func(Of T, Boolean))(b, e) Return query.Where(lambda) End Function It works fine and is consumed in this way query = ETForGreaterThan(query, Value, propertyInfo) As you can see, I give it an IQueryable collection and it add a where clause to it, base on a property and a value. Y can construct Lessthan, LessOrEqualThan etc equivalents as Expression has this operators predefined. ¿How can I transform this code to do the same with strings? Expression don't give me a predefined operator like "contains" or "startwith" and I'm really noob with Expression trees. Thanks, and please Post your answer in C#/VB. Choose the one that make you feel more confortable.

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• To use package properly, how to arrange directory, file name, unit test file?

  - by Stephen Hsu

  My source files tree is like this: /src /pkg /foo foo.go foo_test.go Inside foo.go: package foo func bar(n int) { ... } inside foo_test.go: package foo func testBar(t *testing.T) { bar(10) ... } My questions are: Does package name relates to directory name, source file name? If there is only one source file for a package, need I put it in a directory? Should I put foo.go and foo_test.go in the same package? In the foo_test.go, as it's in the same package as foo.go, I didn't import foo. But when I compile foo_test.go with 6g, it says bar() is undefined. What should I do?

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• C++: How do I pass a function(without knowing its parameters) to another function?

  - by Ninja

  Hi all. I'm trying to create a function that will store and repeat another function given as a parameter for a specific amount of time or repeats given. But when you want to pass a function as a parameter you have to know all of its parameters before hand. How would I do if I wanted to pass the function as one parameter, and the parameters as another? void AddTimer(float time, int repeats, void (*func), params); // I know params has no type and that (*func) is missing parameters but it is just to show you what I mean Thanks in advance

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• testing existing attribute of a @classmethod function, yields AttributeError

  - by alex

  i have a function which is a class method, and i want to test a attribute of the class which may or may not be None, but will exist always. class classA(): def __init__(self, var1, var2 = None): self.attribute1 = var1 self.attribute2 = var2 @classmethod def func(self,x): if self.attribute2 is None: do something i get the error AttributeError: class classA has no attribute 'attributeB' when i access the attribute like i showed but if on command line i can see it works, x = classA() x.attributeB is None True so the test works. if i remove the @classmethod decorator from func, the problem disapears. if i leave the @classmethod decorator, it only seems to affect variables which are supplied default values in the super-class's constructor. whats going on in the above code?

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• Use C function in C++ program; "multiply-defined" error

  - by eom

  I am trying to use this code for the Porter stemming algorithm in a C++ program I've already written. I followed the instructions near the end of the file for using the code as a separate module. I created a file, stem.c, that ends after the definition and has extern int stem(char * p, int i, int j) ... It worked fine in Xcode but it does not work for me on Unix with gcc 4.1.1--strange because usually I have no problem moving between the two. I get the error ld: fatal: symbol `stem(char*, int, int)' is multiply-defined: (file /var/tmp//ccrWWlnb.o type=FUNC; file /var/tmp//cc6rUXka.o type=FUNC); ld: fatal: File processing errors. No output written to cluster I've looked online and it seems like there are many things I could have wrong, but I'm not sure what combination of a header file, extern "C", etc. would work.

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• Why doesn't functools.partial return a real function (and how to create one that does)?

  - by epsilon

  So I was playing around with currying functions in Python and one of the things that I noticed was that functools.partial returns a partial object rather than an actual function. One of the things that annoyed me about this was that if I did something along the lines of: five = partial(len, 'hello') five('something') then we get TypeError: len() takes exactly 1 argument (2 given) but what I want to happen is TypeError: five() takes no arguments (1 given) Is there a clean way to make it work like this? I wrote a workaround, but it's too hacky for my taste (doesn't work yet for functions with varargs): def mypartial(f, *args): argcount = f.func_code.co_argcount - len(args) params = ''.join('a' + str(i) + ',' for i in xrange(argcount)) code = ''' def func(f, args): def %s(%s): return f(*(args+(%s))) return %s ''' % (f.func_name, params, params, f.func_name) exec code in locals() return func(f, args)

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• Order of execution and style of coding in Python

  - by Jason

  Hi guys. I am new to Python so please don't flame me if the question is too basic :) I have read that Python is executed from top - to - bottom. If this is the case, why do programs go like this: def func2(): def func1(): #call func2() def func() #call func1() if __name__ == '__main__': call func() So from what I have seen, the main function goes at last and the other functions are stacked on top of it. Am I wrong in saying this? If no, why isn't the main function or the function definitions written from top to bottom?

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• Function to register functions to be called if event invoked.

  - by zaidwaqi

  Hi, I have a Panel which contains 20 PictureBox controls. If a user clicks on any of the controls, I want a method within the Panel to be called. How do I do this? public class MyPanel : Panel { public MyPanel() { for(int i = 0; i < 20; i++) { Controls.Add(new PictureBox()); } } // DOESN'T WORK. // function to register functions to be called if the pictureboxes are clicked. public void RegisterFunction( <function pointer> func ) { foreach ( Control c in Controls ) { c.Click += new EventHandler( func ); } } } How do I implement RegisterFunction()? Also, if there are cool C# features that can make the code more elegant, please share. Thanks.

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• F# - Function with no arguments?

  - by Rubys

  When thinking in a functional mindset, given that functions are supposed to be pure, one can conclude any function with no arguments is basically just a value. However, reallity gets in the way, and with different inputs, I might not need a certain function, and if that function is computationally expensive, I'd like to not evaluate it if it's not needed. I found a workaround, using let func _ = ... and calling it with func 1 or whatever, but that feels very non-idiomatic and confusing to the reader. This boils down to one question: In F#, Is there a proper way to declare a function with zero arguments, without having it evaluated on declaration?

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• does overload operator-> a compile time action?

  - by Brent

  when I tried to compile the code: struct S { void func2() {} }; class O { public: inline S* operator->() const; private: S* ses; }; inline S* O::operator->() const { return ses; } int main() { O object; object->func(); return 0; } there is a compile error reported: D:\code>g++ operatorp.cpp -S -o operatorp.exe operatorp.cpp: In function `int main()': operatorp.cpp:27: error: 'struct S' has no member named 'func' it seems that invoke the overloaded function of "operator-" is done during compile time? I'd add "-S" option for compile only.

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• Confusion regarding a function definition in C

  - by user34790

  I found this function definition void *func(void *param) { } Actually, I have a certain confusion regarding this function definition. What does void * mean in the return type of the function as well as the argument. I am a beginner in C. So please don't mind. Thank you void *func(void *param) { int s = (int)param; .... } Well looking at the above program which I found. I think it should have been int *s = (int *)param; isn't it? I am confused

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• Using SQLAlchemy, how can I return a count with multiple columns

  - by Andy

  I am attempting to run a query like this: SELECT comment_type_id, name, count(comment_type_id) FROM comments, commenttypes WHERE comment_type_id=commenttypes.id GROUP BY comment_type_id Without the join between comments and commenttypes for the name column, I can do this using: session.query(Comment.comment_type_id,func.count(Comment.comment_type_id)).group_by(Comment.comment_type_id).all() However, if I try to do something like this, I get incorrect results: session.query(Comment.comment_type_id, Comment.comment_type, func.count(Comment.comment_type_id)).group_by(Comment.comment_type_id).all() I have two problems with the results: (1, False, 82920) (2, False, 588) (3, False, 4278) (4, False, 104370) Problems: The False is not correct The counts are wrong My expected results are: (1, 'Comment Type 1', 13820) (2, 'Comment Type 2', 98) (3, 'Comment Type 2', 713) (4, 'Comment Type 2', 17395) How can I adjust my command to pull the correct name value and the correct count?

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• closing sockets on linux and windows

  - by robUK

  Hello, gcc 4.4.4 c89 Visual Studio VC++ 2008 I am writing a cross platform client server application. It will run on both linux and windows. However, I am just wondering what I have done for closing the sockets is correct. I close the file descriptor. However, if there is a problem with closing it. What is the best way to handle this. Maybe some data is still being sent or received? Many thanks for any advice, if(close(sockfd) == -1) { #if defined ( _WIN32 ) fprintf(stderr, "[ %d ] [ %s ] [ %s ] [ %d ]\n", WSAGetLastError(), strerror(errno), __func__, __LINE__); #elif( __linux__ ) fprintf(stderr, "[ %s ] [ %s ] [ %d ]\n", strerror(errno), __func__, __LINE__); #endif return CS_FAILURE; }

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• Method to register method to be called when event is raised

  - by zaidwaqi

  I have a Panel which contains 20 PictureBox controls. If a user clicks on any of the controls, I want a method within the Panel to be called. How do I do this? public class MyPanel : Panel { public MyPanel() { for(int i = 0; i < 20; i++) { Controls.Add(new PictureBox()); } } // DOESN'T WORK. // function to register functions to be called if the pictureboxes are clicked. public void RegisterFunction( <function pointer> func ) { foreach ( Control c in Controls ) { c.Click += new EventHandler( func ); } } } How do I implement RegisterFunction()? Also, if there are cool C# features that can make the code more elegant, please share.

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• javascript var declaration within loop

  - by Trouts

  hello, /*Test scope problem*/ for(var i=1; i<3; i++){ //declare variables var no = i; //verify no alert('setting '+no); //timeout to recheck setTimeout(function(){ alert('test '+no); }, 500); } it alerts "setting 1" and "setting 2" as expected, but after the timeout it outputs "test 2" twice - for some reason the variable "no" is not reset after the first loop... i've found only an "ugly" workaround... /*Test scope problem*/ var func=function(no){ //verify no alert('setting '+no); //timeout to recheck setTimeout(function(){ alert('test '+no); }, 500); } for(var i=1; i<3; i++){ func(i); } Any ideas on how to workaround this problem in a more direct way? or is this the only way?

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