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  • Program always returns binary '>>' : no operator found which takes a left-hand operand of type error

    - by Tom Ward
    So I've been set a task to create a temperature converter in C++ using this equation: Celsius = (5/9)*(Fahrenheit – 32) and so far I've come up with this (I've cut out the 10 lines worth of comments from the start so the code posted begins on line 11, if that makes any sense) #include <iostream> #include <string> #include <iomanip> #include <cmath> using namespace std; int main () { float celsius; float farenheit; std::cout << "**************************" << endl; std::cout << "*4001COMP-Lab5-Question 1*" << endl; std::cout << "**************************" << endl << endl; std::cout << "Please enter a temperature in farenheit: "; std::cin >> farenheit >> endl; std::cout << "Temperature (farenheit): " << endl; std::cout << "Temperature (celsius): " << celsius << endl; std::cin.get(); return 0; } Everytime I try to run this program I get a heap of errors with this one appearing every time: 1m:\visual studio 2010\projects\week 5\week 5\main.cpp(26): error C2678: binary '' : no operator found which takes a left-hand operand of type 'std::basic_istream<_Elem,_Traits' (or there is no acceptable conversion) I've tried everything I can think of to get rid of this error but it reappears every time, any idea on how to fix this?

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  • LINQ Except operator and object equality

    - by Abhijeet Patel
    Here is an interesting issue I noticed when using the Except Operator: I have list of users from which I want to exclude some users: The list of users is coming from an XML file: The code goes like this: interface IUser { int ID { get; set; } string Name { get; set; } } class User: IUser { #region IUser Members public int ID { get; set; } public string Name { get; set; } #endregion public override string ToString() { return ID + ":" +Name; } public static IEnumerable<IUser> GetMatchingUsers(IEnumerable<IUser> users) { IEnumerable<IUser> localList = new List<User> { new User{ ID=4, Name="James"}, new User{ ID=5, Name="Tom"} }.OfType<IUser>(); var matches = from u in users join lu in localList on u.ID equals lu.ID select u; return matches; } } class Program { static void Main(string[] args) { XDocument doc = XDocument.Load("Users.xml"); IEnumerable<IUser> users = doc.Element("Users").Elements("User").Select (u => new User { ID = (int)u.Attribute("id"), Name = (string)u.Attribute("name") } ).OfType<IUser>(); //still a query, objects have not been materialized var matches = User.GetMatchingUsers(users); var excludes = users.Except(matches); // excludes should contain 6 users but here it contains 8 users } } When I call User.GetMatchingUsers(users) I get 2 matches as expected. The issue is that when I call users.Except(matches) The matching users are not being excluded at all! I am expecting 6 users ut "excludes" contains all 8 users instead. Since all I'm doing in GetMatchingUsers(IEnumerable users) is taking the IEnumerable and just returning the IUsers whose ID's match( 2 IUsers in this case), my understanding is that by default "Except" will use reference equality for comparing the objects to be excluded. Is this not how "Except" behaves? What is even more interesting is that if I materialize the objects using .ToList() and then get the matching users, and call "Except", everything works as expected! Like so: IEnumerable users = doc.Element("Users").Elements("User").Select (u = new User { ID = (int)u.Attribute("id"), Name = (string)u.Attribute("name") } ).OfType().ToList(); //explicity materializing all objects by calling ToList() var matches = User.GetMatchingUsers(users); var excludes = users.Except(matches); // excludes now contains 6 users as expected I don't see why I should need to materialize objects for calling "Except" given that its defined on IEnumerable? Any suggesstions / insights would be much appreciated.

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  • Confusion over C++ new operator and classes

    - by Nils
    Hi all I created a simple class in C++ which has a private dynamic array. In the constructor I initialize the array using new and in the destructor I free it using delete. When I instantiate the class using Class a = Class(..); it works as expected, however it seems I cannot instantiate it using the new operator (Like Class *a = new Class(..);), I always get a segmentation fault. What I don't understand is when I should use new to instantiate a class and when just call the constructor or should it be possible to instantiate a class either with new or by just calling the constructor. float** A = new float*[3]; for (int i=0; i<3; i++) { A[i] = new float[3]; } A[0][0] = 3; A[0][1] = 3; A[0][2] = 4; A[1][0] = 5; A[1][1] = 6; A[1][2] = 7; A[2][0] = 1; A[2][1] = 2; A[2][2] = 3; Matrix *M = new Matrix(A, 3, 3); delete[] A; delete M; Below the class definition.. class Matrix { private: int width; int height; int stride; float* elements; public: Matrix(float** a, int n, int m); ~Matrix(); }; Matrix::Matrix(float** a, int n, int m) { // n: num rows // m: elem per rows elements = new float[n*m]; for (int i=0; i<n; i++) { for (int j=0; j<m; j++) { elements[i*n + j] = a[n][m]; } } } Matrix::~Matrix() { delete[] elements; }

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  • trying to make a simple grid-class, non-lvalue in assignment

    - by Tyrfing
    I'm implementing a simple C++ grid class. One Function it should support is accessed through round brackets, so that I can access the elements by writing mygrid(0,0). I overloaded the () operator and i am getting the error message: "non-lvalue in assignment". what I want to be able to do: //main cGrid<cA*> grid(5, 5); grid(0,0) = new cA(); excerpt of my implementation of the grid class: template class cGrid { private: T* data; int mWidth; int mHeight; public: cGrid(int width, int height) : mWidth(width), mHeight(height) { data = new T[width*height]; } ~cGrid() { delete data; } T operator ()(int x, int y) { if (x >= 0 && x <= mWidth) { if (y >= 0 && y <= mHeight) { return data[x + y * mWidth]; } } } const T &operator ()(int x, int y) const { if (x >= 0 && x <= mWidth) { if (y >= 0 && y <= mHeight) { return data[x + y * mWidth]; } } } The rest of the code deals with the implementation of an iterator and should not be releveant.

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  • Why does this cast to Base class in virtual function give a segmentation fault?

    - by dehmann
    I want to print out a derived class using the operator<<. When I print the derived class, I want to first print its base and then its own content. But I ran into some trouble (see segfault below): class Base { public: friend std::ostream& operator<<(std::ostream&, const Base&); virtual void Print(std::ostream& out) const { out << "BASE!"; } }; std::ostream& operator<<(std::ostream& out, const Base& b) { b.Print(out); return out; } class Derived : public Base { public: virtual void Print(std::ostream& out) const { out << "My base: "; //((const Base*)this)->Print(out); // infinite, calls this fct recursively //((Base*)this)->Print(out); // segfault (from infinite loop?) ((Base)*this).Print(out); // OK out << " ... and myself."; } }; int main(int argc, char** argv){ Derived d; std::cout << d; return 0; } Why can't I cast in one of these ways? ((const Base*)this)->Print(out); // infinite, calls this fct recursively ((Base*)this)->Print(out); // segfault (from infinite loop?)

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  • What am i doing wrong

    - by Erik Sapir
    I have the following code. I need B class to have a min priority queue of AToTime objects. AToTime have operator, and yet i receive error telling me than there is no operator matching the operands... #include <queue> #include <functional> using namespace std; class B{ //public functions public: B(); virtual ~B(); //private members private: log4cxx::LoggerPtr m_logger; class AToTime { //public functions public: AToTime(const ACE_Time_Value& time, const APtr a) : m_time(time), m_a(a){} bool operator >(const AToTime& other) { return m_time > other.m_time; } //public members - no point using any private members here public: ACE_Time_Value m_time; APtr m_a; }; priority_queue<AToTime, vector<AToTime>, greater<AToTime> > m_myMinHeap; };

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  • User Defined Conversions in C++

    - by wash
    Recently, I was browsing through my copy of the C++ Pocket Reference from O'Reilly Media, and I was surprised when I came across a brief section and example regarding user-defined conversion for user-defined types: #include <iostream> class account { private: double balance; public: account (double b) { balance = b; } operator double (void) { return balance; } }; int main (void) { account acc(100.0); double balance = acc; std::cout << balance << std::endl; return 0; } I've been programming in C++ for awhile, and this is the first time I've ever seen this sort of operator overloading. The book's description of this subject is somewhat brief, leaving me with a few unanswered questions about this feature: Is this a particularly obscure feature? As I said, I've been programming in C++ for awhile and this is the first time I've ever come across this. I haven't had much luck finding more in-depth material regarding this. Is this relatively portable? (I'm compiling on GCC 4.1) Can user-defined conversions to user defined types be done? e.g. operator std::string () { /* code */ }

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  • Managing a log stream in C++ in a cout-like notation

    - by Andry
    Hello! I have a class in c++ in order to write log files for an application of mine. I have already built the class and it works, it is something like this: class Logger { std::string _filename; public: void print(std::string tobeprinted); } Well, it is intuitive that, in order to print a line in the log file, for an object of Logger, it is simply necessary to do the following: Logger mylogger("myfile.log"); mylogger.print(std::string("This is a log line")); Well. Using a method approach is not the same as using a much better pattern like << is. I would like to do the following: Logger mylogger("myfile.log"); mylogger << "This is a log line"; That's all. I suppose I must overload the << operator... But overloading using this signature (the classic one): ostream& operator<<(ostream& output, const MyObj& o); But I do not have a ostream... So, should I do as follows? Logger& operator<<(Logger& output, const std::string& o); Is this the right way? Thanks

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  • Is there a factory pattern to prevent multiple instances for same object (instance that is Equal) good design?

    - by dsollen
    I have a number of objects storing state. There are essentially two types of fields. The ones that uniquely define what the object is (what node, what edge etc), and the others that store state describing how these things are connected (this node is connected to these edges, this edge is part of these paths) etc. My model is updating the state variables using package methods, so all these objects act as immutable to anyone not in Model scope. All Objects extend one base type. I've toyed with the idea of a Factory approach which accepts a Builder object and constructs the applicable object. However, if an instance of the object already exists (ie would return true if I created the object defined by the builder and passed it to the equal method for the existing instance) the factory returns the current object instead of creating a new instance. Because the Equal method would only compare what uniquely defines the type of object (this is node A to node B) but won't check the dynamic state stuff (node A is currently connected to nodes C and E) this would be a way of ensuring anyone that wants my Node A automatically knows its state connections. More importantly it would prevent aliasing nightmares of someone trying to pass an instance of node A with different state then the node A in my model has. I've never heard of this pattern before, and it's a bit odd. I would have to do some overriding of serialization methods to make it work (ensure that when I read in a serilized object I add it to my facotry list of known instances, and/or return an existing factory in its place), as well as using a weakHashMap as if it was a weakHashSet to know whether an instance exists without worrying about a quasi-memory leak occuring. I don't know if this is too confusing or prone to its own obscure bugs. One thing I know is that plugins interface with lowest level hardware. The plugins have to be able to return state that is different than my memory; to tell my memory when its own state is inconsistent. I believe this is possible despite their fetching objects that exist in my memory; we allow building of objects without checking their consistency with the model until the addToModel is called anyways; and the existing plugins design was written before all this extra state existed and worked fine without ever being aware of it. Should I just be using some other design to avoid this crazyness? (I have another question to that affect that I'm posting).

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  • is a factory pattern to prevent multuple instances for same object (instance that is Equal) good design?

    - by dsollen
    I have a number of objects storing state. There are essentially two types of fields. The ones that uniquly define what the object is (what node, what edge etc), and the oens that store state describing how these things are connected (this node is connected to these edges, this edge is part of these paths) etc. My model is updating the state variables using package methdos, so these objects all act as immutable to anyone not in Model scope. All Objects extend one base type. I've toyed with the idea of a Factory approch which accepts a Builder object and construct the applicable object. However, if an instance of the object already exists (ie would return true if I created the object defined by the builder and passed it to the equal method for the existing instance) the factory returns the current object instead of creating a new instance. Because the Equal method would only compare what uniquly defines the type of object (this is node A nto node B) but won't check the dynamic state stuff (node A is currently connected to nodes C and E) this would be a way of ensuring anyone that wants my Node A automatically knows it's state connections. More importantly it would prevent aliasing nightmares of someone trying to pass an instance of node A with different state then the node A in my model has. I've never heard of this pattern before, and it's a bit odd. I would have to do some overiding of serlization methods to make it work (ensure when I read in a serilized object I add it to my facotry list of known instances, and/or return an existing factory in it's place), as well as using a weakHashMap as if it was a weakHashSet to know rather an instance exists without worrying about a quasi-memory leak occuring. I don't know if this is too confusing or prone to it's own obscure bugs. One thing I know is that plugins interface with lowest level hardware. The plugins have to be able to return state taht is different then my memory; to tell my memory when it's own state is inconsistent. I believe this is possible despit their fetching objects that exist in my memory; we allow building of objects without checking their consistency with the model until the addToModel is called anyways; and the existing plugins design was written before all this extra state existed and worked fine without ever being aware of it. Should I just be using some other design to avoid this crazyness? (I have another question to that affect I'm posting).

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  • Who can give me a link for the operator= of vector in MSDN?

    - by 8888q8888
    Who can give me a link for the operator= of vector in MSDN? Why I can only find operator[]? If operator= is just something default, like copy everything in A to B, how this following code works? vector<double> v(100,1); v = vector<double>(200,2); // if operator= is just a trivail version, how to make sure the old v get cleared?

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  • Solaris syslog.conf. What are root and operator?

    - by cjavapro
    In /etc/syslog.conf #ident "@(#)syslog.conf 1.5 98/12/14 SMI" /* SunOS 5.0 */ # # Copyright (c) 1991-1998 by Sun Microsystems, Inc. # All rights reserved. # # syslog configuration file. # # This file is processed by m4 so be careful to quote (`') names # that match m4 reserved words. Also, within ifdef's, arguments # containing commas must be quoted. # *.err;kern.notice;auth.notice /dev/sysmsg *.err;kern.debug;daemon.notice;mail.crit /var/adm/messages *.alert;kern.err;daemon.err operator *.alert root *.emerg * # if a non-loghost machine chooses to have authentication messages # sent to the loghost machine, un-comment out the following line: #auth.notice ifdef(`LOGHOST', /var/log/authlog, @loghost) mail.debug ifdef(`LOGHOST', /var/log/syslog, @loghost) # # non-loghost machines will use the following lines to cause "user" # log messages to be logged locally. # ifdef(`LOGHOST', , user.err /dev/sysmsg user.err /var/adm/messages user.alert `root, operator' user.emerg * ) I googled some and it seems that root and operator mean email to root and to operator. Is this correct?

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  • Do something by operator dial specified number in Asterisk?

    - by Rev
    I want to make ability for Asterisk phone Operators to able do something like this: While operator talking to caller, if Operator dial specified number like 244 (or something like that but not Sip-Userid's), do something (like play sound for caller or etc) for that call. So, Is this possible? Is need to change dialplan? ¦¦¦¦¦ I found this. in first paragraph it's say someething like: if operator dial exten go voiceMail.

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  • Unary NOT/Integersize of the architecture

    - by sid_com
    From "Mastering Perl/Chapter 16/Bit Operators/Unary NOT,~": The unary NOT operator (sometimes called the complement operator), ~, returns the bitwise negation, or 1's complement, of the value, based on integer size of the architecture Why does the following script output two different values? #!/usr/local/bin/perl use warnings; use 5.012; use Config; my $int_size = $Config{intsize} * 8; my $value = 0b1111_1111; my $complement = ~ $value; say length sprintf "%${int_size}b", $value; say length sprintf "%${int_size}b", $complement; Output: 32 64

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  • Implicit array casting in C#

    - by Malki
    Hi, I have the following classes with an implicit cast operator defined: class A { ... } class B { private A m_a; public B(A a) { this.m_a = a; } public static implicit operator B(A a) { return new B(a); } } Now, I can implicitly cast A to B. But why can't I implicitly cast A[] to B[] ? static void Main(string[] args) { // compiles A a = new A(); B b = a; // doesn't compile A[] arrA = new A[] {new A(), new A()}; B[] arrB = arrA; } Thanks, Malki.

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  • Quick, Beginner C++ Overloading Question - Getting the compiler to perceive << is defined for a spec

    - by Francisco P.
    Hello everyone. I edited a post of mine so I coul I overloaded << for a class, Score (defined in score.h), in score.cpp. ostream& operator<< (ostream & os, const Score & right) { os << right.getPoints() << " " << right.scoreGetName(); return os; } (getPoints fetches an int attribute, getName a string one) I get this compiling error for a test in main(), contained in main.cpp binary '<<' : no operator found which takes a right-hand operand of type 'Score' (or there is no acceptable conversion) How come the compiler doesn't 'recognize' that overload as valid? (includes are proper) Thanks for your time.

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  • C++: How to make comparison function for char arrays?

    - by Newbie
    Is this possible? i get weird error message when i put char as the type: inline bool operator==(const char *str1, const char *str2){ // ... } Error message: error C2803: 'operator ==' must have at least one formal parameter of class type ... which i dont understand at all. I was thinking if i could directly compare stuff like: const char *str1 = "something"; const char *str2 = "something else"; const char str3[] = "lol"; // not sure if this is same as above and then compare: if(str1 == str2){ // ... } etc. But i also want it to work with: char *str = new char[100]; and: char *str = (char *)malloc(100); I am assuming every char array i use this way would end in NULL character, so the checking should be possible, but i understand it can be unsafe etc. I just want to know if this is possible to do, and how.

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  • question regarding "this" pointer in c++

    - by sil3nt
    hello there, i have been given class with int variables x and y in private, and an operator overload function, class Bag{ private: int x; int y; public: Bag(); ~Bag(); //....... //.....etc }; Bag operator+ (Bag new) const{ Bag result(*this); //what does this mean? result.x += new.x; result.y += new.y; } What is the effect of having "Bag result(*this);" there?.

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  • LINQ to Entity, using a SQL LIKE operator

    - by Mario
    I have a LINQ to ENTITY query that pulls from a table, but I need to be able to create a "fuzzy" type search. So I need to add a where clause that searches by lastname IF they add the criteria in the search box (Textbox, CAN be blank --- in which case it pulls EVERYTHING). Here is what I have so far: var query = from mem in context.Member orderby mem.LastName, mem.FirstName select new { FirstName = mem.FirstName, LastName = mem.LastName, }; That will pull everything out of the Member table that is in the Entity object. Then I have an addition to the logic: sLastName = formCollection["FuzzyLastName"].ToString(); if (!String.IsNullOrEmpty(sLastName)) query = query.Where(ln => ln.LastName.Contains(sLastName)); The problem is when the search button is pressed, nothing is returned (0 results). I have run the query against the SQL Server that I expect to happen here and it returns 6 results. This is the query I expect: SELECT mem.LastName, mem.FirstName FROM Members mem WHERE mem.LastName = 'xxx' (when xxx is entered into the textbox) Anyone see anything wrong with this?

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  • Javascript || or operator with a undefinded variable

    - by bryan sammon
    I have been doing some reading lately one article I read was from Opera. http://dev.opera.com/articles/view/javascript-best-practices/ In that article they write this: Another common situation in JavaScript is providing a preset value for a variable if it is not defined, like so: if(v){ var x = v; } else { var x = 10; } The shortcut notation for this is the double pipe character: var x = v || 10; For some reason I cant get this to work for me. Is it really possible to check to see if v is defined, if not x = 10? --Thanks. Bryan

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  • index help for a MySQL query using greater-than operator and ORDER BY

    - by Jaymon
    I have a table with at least a couple million rows and a schema of all integers that looks roughly like this: start stop first_user_id second_user_id The rows get pulled using the following queries: SELECT * FROM tbl_name WHERE stop >= M AND first_user_id=N AND second_user_id=N ORDER BY start ASC SELECT * FROM tbl_name WHERE stop >= M AND first_user_id=N ORDER BY start ASC I cannot figure out the best indexes to speed up these queries. The problem seems to be the ORDER BY because when I take that out the queries are fast. I've tried all different types of indexes using the standard index format: ALTER TABLE tbl_name ADD INDEX index_name (index_col_1,index_col_2,...) And none of them seem to speed up the queries. Does anyone have any idea what index would work? Also, should I be trying a different type of index? I can't guarantee the uniqueness of each row so I've avoided UNIQUE indexes. Any guidance/help would be appreciated. Thanks!

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  • DataTable.Select Behaves Strangely Using ISNULL Operator on NULL DateTime Column

    - by Paul Williams
    I have a DataTable with a DateTime column, "DateCol", that can be DBNull. The DataTable has one row in it with a NULL value in this column. I am trying to query rows that have either DBNull value in this column or a date that is greater than today's date. Today's date is 5/11/2010. I built a query to select the rows I want, but it did not work as expected. The query was: string query = "ISNULL(DateCol, '" + DateTime.MaxValue + "'") > "' + DateTime.Today "'" This results in the following query: "ISNULL(DateCol, '12/31/9999 11:59:59 PM') > '5/11/2010'" When I run this query, I get no results. It took me a while to figure out why. What follows is my investigation in the Visual Studio immediate window: > dt.Rows.Count 1 > dt.Rows[0]["DateCol"] {} > dt.Rows[0]["DateCol"] == DBNull.Value true > dt.Select("ISNULL(DateCol,'12/31/9999 11:59:59 PM') > '5/11/2010'").Length 0 <-- I expected 1 Trial and error showed a difference in the date checks at the following boundary: > dt.Select("ISNULL(DateCol, '12/31/9999 11:59:59 PM') > '2/1/2000'").Length 0 > dt.Select("ISNULL(DateCol, '12/31/9999 11:59:59 PM') > '1/31/2000'").Length 1 <-- this was the expected answer The query works fine if I wrap the DateTime field in # instead of quotes. > dt.Select("ISNULL(DateCol, #12/31/9999#) > #5/11/2010#").Length 1 My machine's regional settings is currently set to EN-US, and the short date format is M/d/yyyy. Why did the original query return the wrong results? Why would it work fine if the date was compared against 1/31/2000 but not against 2/1/2000?

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  • Regex not operator

    - by Erik Goens
    I need to use a regex to pull a value out a url domain that will exclude everything but the host (ex: wordpress) and domain type (ex .com). The urls are dynamic and contain 2-3 values for each result (www.example.com or example.org). I am trying to use this expression, but I am only getting back the first letter of every item I am attempting to exclude: Expresssion (?!wordpress|com|www)(\w+|\d+) String example.wordpress.com Results example ordpress om Desired Result example Any assistance would be greatly appreciated

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  • Cocoa @sum array operator too slow - alternatives?

    - by icodestuff
    I've got a text field value bound to a key path that uses @sum. When the array controller is filtered, the text field updates properly, but extremely slowly, lagging the UI or outright beachballing after every key press (less so as the number of items in arrangedObjects decreases). There is no lag if I don't use @sum; I've narrowed it down to this. Is there a faster way to do the same thing?

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