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  • Trying to overload + operator

    - by FrostyStraw
    I cannot for the life of me understand why this is not working. I am so confused. I have a class Person which has a data member age, and I just want to add two people so that it adds the ages. I don't know why this is so hard, but I'm looking for examples and I feel like everyone does something different, and for some reason NONE of them work. Sometimes the examples I see have two parameters, sometimes they only have one, sometimes the parameters are references to the object, sometimes they're not, sometimes they return an int, sometimes they return a Person object. Like..what is the most normal way to do it? class Person { public: int age; //std::string haircolor = "brown"; //std::string ID = "23432598"; Person(): age(19) {} Person operator+(Person&) { } }; Person operator+(Person &obj1, Person &obj2){ Person sum = obj1; sum += obj2; return sum; } I really feel like overloading a + operator should seriously be the easiest thing in the world except I DON'T KNOW WHAT I AM DOING. I don't know if I'm supposed to create the overload function inside the class, outside, if it makes a difference, why if I do it inside it only allows one parameter, I just honestly don't get it.

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  • Visitor and templated virtual methods

    - by Thomas Matthews
    In a typical implementation of the Visitor pattern, the class must account for all variations (descendants) of the base class. There are many instances where the same method content in the visitor is applied to the different methods. A templated virtual method would be ideal in this case, but for now, this is not allowed. So, can templated methods be used to resolve virtual methods of the parent class? Given (the foundation): struct Visitor_Base; // Forward declaration. struct Base { virtual accept_visitor(Visitor_Base& visitor) = 0; }; // More forward declarations struct Base_Int; struct Base_Long; struct Base_Short; struct Base_UInt; struct Base_ULong; struct Base_UShort; struct Visitor_Base { virtual void operator()(Base_Int& b) = 0; virtual void operator()(Base_Long& b) = 0; virtual void operator()(Base_Short& b) = 0; virtual void operator()(Base_UInt& b) = 0; virtual void operator()(Base_ULong& b) = 0; virtual void operator()(Base_UShort& b) = 0; }; struct Base_Int : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_Long : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_Short : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_UInt : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_ULong : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_UShort : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; Now that the foundation is laid, here is where the kicker comes in (templated methods): struct Visitor_Cout : public Visitor { template <class Receiver> void operator() (Receiver& r) { std::cout << "Visitor_Cout method not implemented.\n"; } }; Intentionally, Visitor_Cout does not contain the keyword virtual in the method declaration. All the other attributes of the method signatures match the parent declaration (or perhaps specification). In the big picture, this design allows developers to implement common visitation functionality that differs only by the type of the target object (the object receiving the visit). The implementation above is my suggestion for alerts when the derived visitor implementation hasn't implement an optional method. Is this legal by the C++ specification? (I don't trust when some says that it works with compiler XXX. This is a question against the general language.)

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  • Table and Column names causing problems

    - by craig
    I have an issue when the T4 linq templates generate the classes for my MySql db using subsonic 3. It looks like one of our table names "operator" is causing problems in the Context.cs generated class. In the following line of code in Context.cs Visual Studio sees <operator> as a c# operator and generates a compilation error of "Type expected" public Query<operator> operators { get; set; } Is there anyway I can work around this without having to rename my database table and column names? For example hard coding something in Settings.ttinclude to use or map different names to specific db tables and columns?

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  • explicit copy constructor or implicit parameter by value

    - by R Samuel Klatchko
    I recently read (and unfortunately forgot where), that the best way to write operator= is like this: foo &operator=(foo other) { swap(*this, other); return *this; } instead of this: foo &operator=(const foo &other) { foo copy(other); swap(*this, copy); return *this; } The idea is that if operator= is called with an rvalue, the first version can optimize away construction of a copy. So when called with a rvalue, the first version is faster and when called with an lvalue the two are equivalent. I'm curious as to what other people think about this? Would people avoid the first version because of lack of explicitness? Am I correct that the first version can be better and can never be worse?

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  • Overloading new, delete in C++

    - by user265260
    i came across this line is stroustrup An operator function must either be a member or take at least one argument of a user-defined type (functions redefining the new and delete operators need not). Dont operator new and operator delete take an user defined type as one of their arguments? what does it mean, am i missing something here

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  • C++ Code Clarification Needed..

    - by ke3pup
    Hi guys I'm trying to understand what the code below says: struct compare_pq; struct compare_pq { bool operator() (Events *& a, Events *& b); }; std::priority_queue<Events *, std::vector<Events *>, compare_pq> eventList; i looked at what priority_queue is and how its declared but can't quit understand what compare_pq is doing in the priority_queue eventList. Also what does operator() do since i've never seen *& before and empty operator overloading operator()! any help would be appreciated. Thank you

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  • What is the best signature for overloaded arithmetic operators in C++?

    - by JohnMcG
    I had assumed that the canonical form for operator+, assuming the existence of an overloaded operator+= member function, was like this: const T operator+(const T& lhs, const T& rhs) { return T(lhs) +=rhs; } But it was pointed out to me that this would also work: const T operator+ (T lhs, const T& rhs) { return lhs+=rhs; } In essence, this form transfers creation of the temporary from the body of the implementation to the function call. It seems a little awkward to have different types for the two parameters, but is there anything wrong with the second form? Is there a reason to prefer one over the other?

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  • Django/Mod_WSGI error: UnboundLocalError: local variable 'resolver' referenced before assignment

    - by ycseattle
    Hello, I've setup the Django with mod_wsgi and run into this error. I thought maybe the sys.path was not setup correctly but I tried everything I could think of with no luck. Any suggestions? The following is the apache2 log for the error: mod_wsgi (pid=2579): Exception occurred processing WSGI script '/home/myapp/myapp.wsgi'. Traceback (most recent call last): File "/usr/local/lib/python2.6/dist-packages/django/core/handlers/wsgi.py", line 241, in __call__ response = self.get_response(request) File "/usr/local/lib/python2.6/dist-packages/django/core/handlers/base.py", line 142, in get_response return self.handle_uncaught_exception(request, resolver, exc_info) UnboundLocalError: local variable 'resolver' referenced before assignment The following is the content in the myapp.wsgi: import os import sys # put the Django project on sys.path sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), "../"))) os.environ["DJANGO_SETTINGS_MODULE"] = "photopier.settings" #os.environ["PYTHONPATH"]="/home" from django.core.handlers.wsgi import WSGIHandler application = WSGIHandler()

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  • Assignment in python for loop possible?

    - by flyingcrab
    I have a dictionary d (and a seperate sorted list of keys, keys). I wanted the loop to only process entries where the value is False - so i tried the following: for key in keys and not d[key]: #do foo I suppose my understanding of python sytax is not what i thought it was - because the assignment doesnt suppose to have happened above, and a i get an instanciation error. The below works of course, but I'd really like to be able to use something like the code above.. possible? for key in keys: if d[key]: continue #foo time! Thanks!

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  • "The left hand side of an assignment must be a variable" due to extra parentheses

    - by polygenelubricants
    I know why the following code doesn't compile: public class Main { public static void main(String args[]) { main((null)); // this is fine! (main(null)); // this is NOT! } } What I'm wondering is why my compiler (javac 1.6.0_17, Windows version) is complaining "The left hand side of an assignment must be a variable". I'd expect something like "Don't put parentheses around a method invokation, dummy!", instead. So why is the compiler making a totally unhelpful complaint about something that is blatantly irrelevant? Is this the result of an ambiguity in the grammar? A bug in the compiler? If it's the former, could you design a language such that a compiler would never be so off-base about a syntax error like this?

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  • Assignment to None

    - by Joel
    Hello, I have a function which returns 3 numbers, e.g.: def numbers(): return 1,2,3 usually I call this function to receive all three returned numbers e.g.: a,b,c=numbers() However, I have one case in which I only need the first returned number. I tried using: a, None None = numbers() But I receive "SyntaxError: assignment to None". I know, of course, that i can use the first option I mentioned and then not use "b" and "c", but only "a". However, this seems like a "waste" of two vars and feels like wrong programming. Any ideas? Thanks, Joek

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  • Formatting a barcode with hyphens in between - Assignment question

    - by capex
    Hi, The assignment at my first year uni computing course says my program should read a barcode number, and then display the same 13 digit barcode number separated by hyphens. For example, 9300675016902 should look like 930-067501-690-1. The restrictions say I can't use the following: No arrays No strings No functions. Any directions on this? (So far I have done this: part1 = barcode/10000000000; which gives me the first three digits, and this: part4 = barcode%10; which gives me the last digit. Thanks in advance!

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  • JavaScript function binding (this keyword) is lost after assignment

    - by Ding
    this is one of most mystery feature in JavaScript, after assigning the object method to other variable, the binding (this keyword) is lost var john = { name: 'John', greet: function(person) { alert("Hi " + person + ", my name is " + this.name); } }; john.greet("Mark"); // Hi Mark, my name is John var fx = john.greet; fx("Mark"); // Hi Mark, my name is my question is: 1) what is happening behind the assignment? var fx = john.greet; is this copy by value or copy by reference? fx and john.greet point to two diferent function, right? 2) since fx is a global method, the scope chain contains only global object. what is the value of this property in Variable object?

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  • Objective-C member variable assignment?

    - by Alex
    I have an objective-c class with member variables. I am creating getters and setters for each one. Mostly for learning purposes. My setter looks like the following: - (void) setSomething:(NSString *)input { something = input; } However, in C++ and other languages I have worked with in the past, you can reference the member variable by using the this pointer like this->something = input. In objective-c this is known as self. So I was wondering if something like that is possible in objective-c? Something like this: - (void) setSomething:(NSString *)input { [self something] = input; } But that would call the getter for something. So I'm not sure. So my question is: Is there a way I can do assignment utilizing the self pointer? If so, how? Is this good practice or is it evil? Thanks!

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  • TypeError: 'NoneType' object does not support item assignment

    - by R S John
    I am trying to do some mathematical calculation according to the values at particular index of a NumPy array with the following code X = np.arange(9).reshape(3,3) temp = X.copy().fill(5.446361E-01) ind = np.where(X < 4.0) temp[ind] = 0.5*X[ind]**2 - 1.0 ind = np.where(X >= 4.0 and X < 9.0) temp[ind] = (5.699327E-1*(X[ind]-1)**4)/(X[ind]**4) print temp But I am getting the following error Traceback (most recent call last): File "test.py", line 7, in <module> temp[ind] = 0.5*X[ind]**2 - 1.0 TypeError: 'NoneType' object does not support item assignment Would you please help me in solving this? Thanks

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  • error: incompatible types in assignment

    - by ambika
    My C code #include <stdio.h> #include <stdlib.h> #include "help.h" int test(int x, P *ut) { int point = 10; ut->dt[10].max_x = NULL; } int main(int argc, char** argv) { return (EXIT_SUCCESS); } my help.h file code typedef struct{ double max_x; double max_y; }X; typedef struct{ X dt[10]; }P; I got an error i.e error: incompatible types in assignment error comes in here ut->dt[10].max_x = NULL; can anybody help me. thanks in advance.

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  • help in security assignment

    - by scatman
    i have to write a program that sniffs network packets (part1-the simple part). and i have to update the program (part2) so that it will be able to terminate connections. the specific requirements are: construct raw packets by specifying data link layer and network layer information including appropriate source and destination MAC and IP addresses. These packets are intended to terminate the connection. To do so, you should used SOCK_RAW as the socket type to be able to set the header information by yourself. can anybody give me some ideas on the second part? should i hijack the session,apply a dos attack on one of the users?? all i need is some tips of how to terminate the connection. i am using c programming language. and this is a course assignment for the security course.

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  • Flash AS3: automate property assignment to new instance from arguments in constructor

    - by matt lohkamp
    I like finding out about tricky new ways to do things. Let's say you've got a class with a property that gets set to the value of an argument in the constructor, like so: package{ public class SomeClass{ private var someProperty:*; public function SomeClass(_someProperty:*):void{ someProperty = _someProperty; } } } That's not exactly a hassle. But imagine you've got... I don't know, five properties. Ten properties, maybe. Rather then writing out each individual assignment, line by line, isn't there a way to loop through the constructor's arguments and set the value of each corresponding property on the new instance accordingly? I don't think that the ...rest or arguments objects will work, since they only keep an enumerated list of the arguments, not the argument names - I'm thinking something like this would be better: for(var propertyName:String in argsAsAssocArray){this[propertyName] = argsAsAssocArray[propertyName];} ... does something like this exist?

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  • assignment vs std::swap and merging and keeping duplicates in seperate object

    - by rubenvb
    Say I have two std::set<std::string>s. The first one, old_options, needs to be merged with additional options, contained in new_options. I can't just use std::merge (well, I do, but not only that) because I also check for doubles and warn the user about this accordingly. To this effect, I have void merge_options( set<string> &old_options, const set<string> &new_options ) { // find duplicates and create merged_options, a stringset containing the merged options // handle duplicated the way I want to // ... old_options = merged_options; } Is it better to use std::swap( merged_options, old_options ); or the assignment I have? Is there a better way to filter duplicates and return the merged set than consecutive calls to std::set_intersection and std::set_union to detect dupes and merge the sets? I know it's slower than one traversal and doing both at once, but these sets are small (performance is not critical) and I trust the Standard more than I trust myself.

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  • simple assignment not working for me: iphone sdk

    - by tak
    Hi all. Can someone please explain to me why this simple assignment doesn't work. Here is the code loanDetails.currency = myCurrency; NSLog(@" Value %@",myCurrency); NSLog(@" Value %@",loanDetails.currency); NSLog(@" Value %@",myCurrency); the output is:- 2010-05-05 23:00:44.394 ExpenseTracker[3576:207] Value AFA 2010-05-05 23:00:44.750 ExpenseTracker[3576:207] Value (null) 2010-05-05 23:00:45.095 ExpenseTracker[3576:207] Value AFA And the definition is as: @property (nonatomic,retain) NSString *currency;

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  • rspec mocking object property assignment

    - by charlielee
    I have a rspec mocked object, a value is assign to is property. I am struggleing to have that expectation met in my rspec test. Just wondering what the sytax is? The code: def create @new_campaign = AdCampaign.new(params[:new_campaign]) @new_campaign.creationDate = "#{Time.now.year}/#{Time.now.mon}/#{Time.now.day}" if @new_campaign.save flash[:status] = "Success" else flash[:status] = "Failed" end end The test it "should able to create new campaign when form is submitted" do campaign_model = mock_model(AdCampaign) AdCampaign.should_receive(:new).with(params[:new_campaign]).and_return(campaign_model) campaign_model.should_receive(:creationDate).with("#{Time.now.year}/#{Time.now.mon}/#{Time.now.day}")campaign_model.should_receive(:save).and_return(true) post :create flash[:status].should == 'Success' response.should render_template('create') end The problem is I am getting this error: Spec::Mocks::MockExpectationError in 'CampaignController new campaigns should able to create new campaign when form is submitted' Mock "AdCampaign_1002" received unexpected message :creationDate= with ("2010/5/7") So how do i set a expectation for object property assignment? Thanks

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  • assignment makes pointer from integer without a cast

    - by mrblippy
    hi, i am trying to make a linked list and create some methods. but i am getting the error assignment makes pointer from integer without a cast. #include <stdio.h> #include <stdlib.h> #include "students.h" node_ptr create(void) { node_ptr students = (node_ptr) malloc(sizeof(struct node)); students->ID = 0; students->name = NULL; students->next = NULL; return students; } void insert_in_order(int n, node_ptr list) { node_ptr before = list; node_ptr new_node = (node_ptr) malloc(sizeof(struct node)); new_node->ID = n;//error is here i think while(before->next && (before->next->ID < n)) { before = before->next; } new_node->next = before->next; before->next = new_node; }

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  • cannot convert ‘mcontext_t*’ to ‘sigcontext*’ in assignment

    - by user353573
    i have checked asm/ucontext.h it should be sigcontext, but why pop up the error message cannot convert ‘mcontext_t*’ to ‘sigcontext*’ in assignment #include <stdio.h> #include <signal.h> #include <asm/ucontext.h> static unsigned long target; void handler(int signum, siginfo_t *siginfo, void *uc0){ struct ucontext *uc; struct sigcontext *sc; uc = (struct ucontext *)uc0; sc = &uc->uc_mcontext; sc->eip = target; } struct ucontext { unsigned long uc_flags; struct ucontext *uc_link; stack_t uc_stack; struct sigcontext uc_mcontext; sigset_t uc_sigmask; /* mask last for extensibility */ };

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  • JS assignment order of properties in objects

    - by devdev
    Just had a quick question about why a certain order of assignment works and another doesn't. I wanted to create a simple "inherit" / "copy" function (just for testing it) that copies properties from one object to another: var cat = { tail:"yes", hairy:"yes, hairy" }; var dog = { sick:"extremely ill"}; function inherit(obj1, obj2) { for (var p in obj1) { obj2[p] = obj1[p]; // this works, but "obj1[p] = obj2[p];" doesn't. Why?? } } inherit(cat, dog); console.log(dog.tail);

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