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  • Why "constructor-way" of declaring variable in "for-loop" allowed but in "if-statement" not allowed?

    - by PiotrNycz
    Consider this simple example: /*1*/ int main() { /*2*/ for (int i(7); i;){break;} /*3*/ if (int i(7)) {} /*4*/ } Why line-2 compiles just fine, whilst line-3 gives the error? This is little strange to me why if-statement is in this aspect treated worse than for-loop? If this is compiler specific - I tested with gcc-4.5.1: prog.cpp: In function 'int main()': prog.cpp:3:7: error: expected primary-expression before 'int' prog.cpp:3:7: error: expected ')' before 'int' I was inspired by this question [UPDATE] I know this compiles just fine: /*1*/ int main() { /*2*/ for (int i = 7; i;){break;} /*3*/ if (int i = 7) {} /*4*/ }

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  • Can I execute a "variable statements" within a function and without defines.

    - by René Nyffenegger
    I am facing a problem that I cannot see how it is solvable without #defines or incuring a performance impact although I am sure that someone can point me to a solution. I have an algorithm that sort of produces a (large) series of values. For simplicity's sake, in the following I pretend it's a for loop in a for loop, although in my code it's more complex than that. In the core of the loop I need to do calculations with the values being produced. Although the algorithm for the values stays the same, the calculations vary. So basically, what I have is: void normal() { // "Algorithm" producing numbers (x and y): for (int x=0 ; x<1000 ; x++) { for (int y=0 ; y<1000 ; y++) { // Calculation with numbers being produced: if ( x+y == 800 && y > 790) { std::cout << x << ", " << y << std::endl; } // end of calculation }} } So, the only part I need to change is if ( x+y == 800 && y > 790) { std::cout << x << ", " << y << std::endl; } So, in order to solve that, I could construct an abstract base class: class inner_0 { public: virtual void call(int x, int y) = 0; }; and derive a "callable" class from it: class inner : public inner_0 { public: virtual void call(int x, int y) { if ( x+y == 800 && y > 790) { std::cout << x << ", " << y << std::endl; } } }; I can then pass an instance of the class to the "algorithm" like so: void O(inner i) { for (int x=0 ; x<1000 ; x++) { for (int y=0 ; y<1000 ; y++) { i.call(x,y); }} } // somewhere else.... inner I; O(I); In my case, I incur a performance hit because there is an indirect call via virtual function table. So I was thinking about a way around it. It's possible with two #defines: #define OUTER \ for (int x=0 ; x<1000 ; x++) { \ for (int y=0 ; y<1000 ; y++) { \ INNER \ }} // later... #define INNER \ if (x + y == 800 && y > 790) \ std::cout << x << ", " << y << std::endl; OUTER While this certainly works, I am not 100% happy with it because I don't necessarly like #defines. So, my question: is there a better way for what I want to achieve?

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  • Is there a straightforward way to have a thread-local instance variable?

    - by Dan Tao
    With the ThreadStatic attribute I can have a static member of a class with one instance of the object per thread. This is really handy for achieving thread safety using types of objects that don't guarantee thread-safe instance methods (e.g., System.Random). It only works for static members, though. Is there any straightforward way to declare a class member as thread-local, meaning, each class instance gets an object per thread?

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  • How to declare a pointer to a variable as a parameter of a function in C++?

    - by Keand64
    I have a function that takes a pointer to a D3DXVECTOR3, but I have no reason to declare this beforehand. The most logical solution to me was using new: Function( //other parameters, new D3DXVECTOR3(x, y, 0)); but I don't know how I would go about deleting it, beign intitialized in a function. My next thought was to use the & operator, like so: Function( //other parameters, &D3DVECTOR3(x, y, 0)); but I don't know if this is a valid way to go about doing this. (It doesn't get an error, but neither does int *x; x = 50;). So should I use new, &, or some other technique I'm overlooking?

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  • How can i use a variable created in a objective c Void function?

    - by James
    Im trying to get the lat and long values generated in a void function and use them within another function. Any help grateful. (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation { float latDeg = newLocation.coordinate.latitude; NSLog(@"Lat: %g", latDeg); float longDeg = newLocation.coordinate.longitude; NSLog(@"Lat: %g", longDeg); } I want to use the latDeg and longDeg variables.

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  • What is the most "database independent" way of creating a variable length text field in a database

    - by Thibaut Colar
    I want to create a text field in the database, with no specific size (it will store text of length unknown in some case) - the particular text are serialized simple object (~ JSON) What is the most database independent way to do this : - a varchar with no size specified (don't think all db support this) - a 'text' field, this seems to be common, but I don't believe it's a standard - a blob or other object of that kind ? - a varchar of a a very large size (that's inefficient and wastes disk space probably) - Other ? I'm using JDBC, but I'd like to use something that is supported in most DB (oracle, mysql, postgresql, derby, HSQL, H2 etc...) Thanks.

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  • What are possible suffixes after variable name in VBA?

    - by archimed7592
    As I've already figured out, there is at least six of them: !@#$%&. Here is snip: Dim A!, B@, C#, D$, E%, F& Debug.Print "A! - " & TypeName(A) Debug.Print "B@ - " & TypeName(B) Debug.Print "C# - " & TypeName(C) Debug.Print "D$ - " & TypeName(D) Debug.Print "E% - " & TypeName(E) Debug.Print "F& - " & TypeName(F) Outputs A! - Single B@ - Currency C# - Double D$ - String E% - Integer F& - Long Where is documentation on this syntax sugar? What other possible suffixes are there? Is there one for Date?

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  • How can I draw a line with a variable of width?

    - by user1729944
    #include <iostream> #include <cmath> #include "graph1.h" using namespace std; int main() { int diameter = 0; int height = 0; double rate = 0; char repeat = 'y'; int obj_num = 0; displayGraphics(); obj_num = drawRect(0,0,50,400); setColor(obj_num,200,200,200); obj_num = drawRect(0,400,640,79); setColor(obj_num,71,35,35); obj_num = drawLine(50,50,150,50,5); setColor(obj_num,80,80,80); displayBMP("faucet.bmp",150,12); do { do { cout << "Enter the diamater of the cylinder <in inches > 0 but <= 300: "; cin >> diameter; if((diameter<0) || (diameter>300)) { cout << "Incorrect diamater entered; value must be between 1 and 300" << endl; } }while((diameter<0) || (diameter>300)); do { cout << "Enter the height of the cylinder <in inches > 0 but <= 325: "; cin >> height; if((height<0) || (height>325)) { cout << "Incorrect height entered; value must be between 1 and 325" << endl; } }while((height<0) || (height>325)); do { cout << "Enter the facet water's rate: <gallons/minute> "; cin >> rate; if((rate<0) || (rate>100)) { cout << "Incorrect rate entered; value must be between 1 and 100" << endl; } }while((rate<0) || (rate>100)); //I need to draw the lines here. The graphics window has a faucet that is supposed to fill //up a cylinder made out of 3 lines. I don't know how to make the lines vary from the users //input since lines are hard coded with points and all i am receiving is the width for the //bottom line and the height for the left and right lines. cout << "Repeat program? (y/n): "; cin >> repeat; clearGraphics(); }while ( (repeat == 'y') || (repeat == 'Y') ); return 0; } Here is a screenshot for reference:

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  • How to run jQuery onClick? Need to pass a variable to run .ajax

    - by user205307
    I'm trying to run .ajax and insert a data element from the onClick of an item from the page. Whats the best way to do this? Something like this: function grabinfo(foo){ $.ajax({ url: "infospitter", method: "GET", data: "id="+foo, success: function(html){ $(#showstuff).html(html); } }); } <input onClick="javascript:grabinfo(18343)" /> // and on page each item will have this button input

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  • How to test that variable is not equal to multiple things? Python

    - by M830078h
    This is the piece of code I have: choice = "" while choice != "1" and choice != "2" and choice != "3": choice = raw_input("pick 1, 2 or 3") if choice == "1": print "1 it is!" elif choice == "2": print "2 it is!" elif choice == "3": print "3 it is!" else: print "You should choose 1, 2 or 3" While it works, I feel that it's really clumsy, specifically the while clause. What if I have more acceptable choices? Is there a better way to make the clause?

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  • jQuery: Quick question. How to select string variable?

    - by user317563
    Hello world, EDIT: I would like to avoid doing something like this: var str = 'Hello'; if ( str == 'Hello') { alert(str); } I would rather do: var str = 'Hello'; $(str).filter(':contains("Hello")').each(function(){ alert(this) }); I've tried a lot of things: $(str).text().method1().method2().method3(); $(str).val().method1().method2().method3(); $(str).contents().method1().method2().method3(); Nothing worked. Is it possible to do this? Thank you for your time. Kind regards, Marius

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  • Printing Variable names and contents as debugging tool; looking for emacs/Python shortcut

    - by Schof
    I find myself adding debugging "print" statements quite often -- stuff like this: print("a_variable_name: %s" % a_variable_name) How do you all do that? Am I being neurotic in trying to find a way to optimize this? I may be working on a function and put in a half-dozen or so of those lines, figure out why it's not working, and then cut them out again. Have you developed an efficient way of doing that? I'm coding Python in Emacs.

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  • How to use PHP Time function to set a time variable of '09:30', add a specific amount of seconds and

    - by Henry
    Hi guys, hopefully you can help me here. I have some code (please see below) which takes the current time, then adds specific seconds to the time and re-displays the time 1 minute in the future. Instead of the time being the current time, I want it to be a time which I set - say 9:30. Then I want to be able to add, for example 65 seconds and it shows me 9:31. Please can you show me how to change it from current time, to a specific time I can set myself. Thank you. <?php $my_time = date('h:i:s',time()); $seconds2add = 65; $new_time= strtotime($my_time); $new_time+=$seconds2add; echo date('h:i:s',$new_time); ?>

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  • Including a C header which declares a variable called "new"?

    - by StackedCrooked
    I'm trying to use the OpenCA library in a C++ application. However, when including the file pki_x509_data_st.h the following code fragment is encountered: typedef struct pki_x509_callbacks_st { /* ---------------- Memory Management -------------------- */ void * (*new) (void ); void (*free) (void *x ); void * (*dup) (void *x ); This won't compile because of the "new" pointer declaration. How can I make it work?

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  • Some confusion with a class variable, but with a twist...

    - by Omega
    I have a class called MyPackage.WebServer and it has a property called DBEngine. I am also dynamically loading a module and class using load_module. Inside this class, it attempts to reference MyPackage.WebServer. When it does though, DBEngine is not set to the value given when WebServer is instantiated. It's the default (None). Would the fact that I'm using load_module cause a different object graph to be created and thus isolate my dynamically loaded class from the rest of my python app?

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