reference

问题 I'm trying to understand if there is any benefit to returning a const reference. I have a factorial function that normally looks like this: unsigned long factorial(unsigned long n) { return (n == 0) ? 1 : n * factorial(n - 1); } I'm assuming that there will be a performance increase when we pass by const reference and we return a const reference... but const -correctness always confuses me. const unsigned long & factorial(const unsigned long& n) { return (n == 0) ? 1 : n * factorial(n - 1); }

问题 Can someone tell me the difference between calling an HTML elment with id="myDomObect"?: var myObj = document.getElementById('myDomObect'); & var myObj = myDomObect; 回答1: Use the first form or a wrapper such as jQuery. The second form, var myObj = myDomObect; Translates to var myObj = window["myDomObect"]; This "works" because of an old, old hack in which ID's were exposed as global window properties (IIRC this was a misfeature from the start) and thus we are still blessed with the behavior

问题 I've been working on this iPhone app for a while now, and I had it completely finished and working. The project I was expanding on was downloaded from a subversion repository online that my professor had given me access too. I accidentally didn't download the "root" copy or something like that, so I wasn't able to commit any changes to the repository. With my instructors help, I downloaded the root copy today and added all my class files to it so I could commit the changes. However, I am now

问题 Does the code crash, because of a circular reference? MenuController: UIViewController - (id)initWithNibName: {... TabsController *tabs = [[TabsController alloc] initWithNibName:@"TabsController" bundle:nil]; self.tab = tabs; .... } //button pressed: - (IBAction)showPrefFromMenu:(id)sender { // todo change delegate!? tab.tabDelegate = self; [self presentModalViewController:tab animated:YES]; //[tab release]; } // delegate method: -(void)myViewDismissed { .... NSLog(@"tab references: %d", [tab

问题 When I read litb answer to this question, I learned that passing an array by reference allows us to obtain its size. I just played little bit with code, and tried to pass a "function" by reference and surprisingly (at least for me), this code compiles: void execute( void (&func)() ) // func is passed by reference! { func(); } Is there any difference between the last function, and this one: void execute( void (*func)() ) // func is passed by pointer! { func(); } I tried it using VC2008, and it

问题 I have Project1 and Project2. Project1 is dependent of Project2. I am sort of tired that every time I make some code changes in Project2, I have to Export Project2 JAR file, and copy it into lib folder of Project1. Is there a way to achieve this automatically? Or, is there any other way to let know Project1 that Project2 had some changes? In Build Path of the project, there is a way to specify references to other projects in Workspace, but this doesn't seem to do anything? What does it

问题 I have a project in Pycharm organized as follows: -- Sources |--__init__.py |--Calculators |--__init__.py |--Filters.py |--Controllers |--__init__.py |--FiltersController.py |--Viewers |--__init__.py |--DataVisualization.py |--Models |--__init__.py |--Data All of my __init__.py, except for the one right above Sources are blank files. I am receiving a lot of warnings of the kind: Cannot find reference 'xxx' in __init__.py For example, my FiltersController .py has this piece of code: import

问题 I heard the temporary objects can only be assigned to constant references. But this code gives error #include <iostream.h> template<class t> t const& check(){ return t(); //return a temporary object } int main(int argc, char** argv){ const int &resCheck = check<int>(); /* fine */ typedef int& ref; const ref error = check<int>(); / *error */ return 0; } The error that is get is invalid initialization of reference of type 'int&' from expression of type 'const int' 回答1: This: typedef int& ref;

问题 string foo() { return "hello"; } int main() { //below should be illegal for binding a non-const (lvalue) reference to a rvalue string& tem = foo(); //below should be the correct one as only const reference can be bind to rvalue(most important const) const string& constTem = foo(); } GCC is the good one to give a compile error : invalid initialization of non-const reference of type std::string& from a temporary of type std::string VS2008 is not too bad as at least it gives a compile warning :

问题 string foo() { return "hello"; } int main() { //below should be illegal for binding a non-const (lvalue) reference to a rvalue string& tem = foo(); //below should be the correct one as only const reference can be bind to rvalue(most important const) const string& constTem = foo(); } GCC is the good one to give a compile error : invalid initialization of non-const reference of type std::string& from a temporary of type std::string VS2008 is not too bad as at least it gives a compile warning :