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  • Would this constructor be acceptable practice?

    - by Robb
    Let's assume I have a c++ class that have properly implemented a copy constructor and an overloaded = operator. By properly implemented I mean they are working and perform a deep copy: Class1::Class1(const Class1 &class1) { // Perform copy } Class1& Class1::operator=(const Class1 *class1) { // perform copy return *this; } Now lets say I have this constructor as well: Class1::Class1(Class1 *class1) { *this = *class1; } My question is would the above constructor be acceptable practice? This is code that i've inherited and maintaining.

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  • Why is 'virtual' optional for overridden methods in derived classes?

    - by squelart
    When a method is declared as virtual in a class, its overrides in derived classes are automatically considered virtual as well, and the C++ language makes this keyword virtual optional in this case: class Base { virtual void f(); }; class Derived : public Base { void f(); // 'virtual' is optional but implied. }; My question is: What is the rationale for making virtual optional? I know that it is not absolutely necessary for the compiler to be told that, but I would think that developers would benefit if such a constraint was enforced by the compiler. E.g., sometimes when I read others' code I wonder if a method is virtual and I have to track down its superclasses to determine that. And some coding standards (Google) make it a 'must' to put the virtual keyword in all subclasses.

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  • Are there cheat sheets for misc source code management tools?

    - by Alex_coder
    I'm looking for something similar to Pacman Rosetta, which explains how to achieve similar tasks using different source code management tools. Sometimes docs for a certain SCM contain examples comparing that particular SCM to a couple of others. But I'm looking for a central place that contains maximum available information. Example: one uses bzr and knows that 'bzr pull' syncs a local repo by fetching new content from a remote repo. One want to know how to do that with git. One finds the git command, he knows the keyword. Since the keyword is known, one can proceed straight to git docs, he knows what to read about, he doesn't have to waste time by searching the git docs. I understand this might be not the only way people use to learn a new SCM tool. If you use other approaches, please do tell.

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  • oracle update procedure problem

    - by murali
    hi, i want to update the following procedure in the oracle table..but it is throwing error CREATE OR REPLACE PROCEDURE update_keywords (aKEYWORD IN VARCHAR2, aCOUNT IN NUMBER) AS BEGIN update searchable_keywords set KEYWORD =:new.aKEYWORD or COUNT =:new.aCOUNT where KEUWORD_ID = : old.KEYWORD_ID; END; this is my procedure, i want to update the keyword & count in the searchable_keywords table with keyword_id(primary key) but it is throwing error as follows... LINE/COL ERROR 3/4 PL/SQL: SQL Statement ignored 4/17 PLS-00049: bad bind variable 'NEW.AKEYWORD' 4/31 PL/SQL: ORA-00933: SQL command not properly ended 4/41 PLS-00049: bad bind variable 'NEW.ACOUNT' can you pls help me slove this problem..thanks

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  • Question regrarding declaring a property

    - by Simon
    Hi. We declare properties using the @property keyword and synthesize it in the implementation file. My question is, What if I declare a property using the @property keyword and also declare a variable in the interface block with the same name? For example, consider the following code, Interface: @interface myClass : NSObject { NSString *myClass_name; // LINE 1 } @property(nonatomic, retain) NSString *myClass_name; // LINE 2 @end Implementation: @implementation myClass @synthesize myClass_name @end Declaring myClass_name in LINE 1 will make any problem? Like any reference problem or any unnecessary memory consumption problem?

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  • Plotting Tweets from DB in Ruby, grouping by hour.

    - by plotti
    Hey guys I've got a couple of issues with my code. I was wondering that I am plotting the results very ineffectively, since the grouping by hour takes ages the DB is very simple it contains the tweets, created date and username. It is fed by the twitter gardenhose. Thanks for your help ! require 'rubygems' require 'sequel' require 'gnuplot' DB = Sequel.sqlite("volcano.sqlite") tweets = DB[:tweets] def get_values(keyword,tweets) my_tweets = tweets.filter(:text.like("%#{keyword}%")) r = Hash.new start = my_tweets.first[:created_at] my_tweets.each do |t| hour = ((t[:created_at]-start)/3600).round r[hour] == nil ? r[hour] = 1 : r[hour] += 1 end x = [] y = [] r.sort.each do |e| x << e[0] y << e[1] end [x,y] end keywords = ["iceland", "island", "vulkan", "volcano"] values = {} keywords.each do |k| values[k] = get_values(k,tweets) end Gnuplot.open do |gp| Gnuplot::Plot.new(gp) do |plot| plot.terminal "png" plot.output "volcano.png" plot.data = [] values.each do |k,v| plot.data << Gnuplot::DataSet.new([v[0],v[1]]){ |ds| ds.with = "linespoints" ds.title = k } end end end

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  • Using a class with const data members in a vector

    - by Max
    Given a class like this: class Foo { const int a; }; Is it possible to put that class in a vector? When I try, my compiler tells me it can't use the default assignment operator. I try to write my own, but googling around tells me that it's impossible to write an assignment operator for a class with const data members. One post I found said that "if you made [the data member] const that means you don't want assignment to happen in the first place." This makes sense. I've written a class with const data members, and I never intended on using assignment on it, but apparently I need assignment to put it in a vector. Is there a way around this that still preserves const-correctness?

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  • non-scalar type requested

    - by lego69
    can somebody please help me with an error conversion from `A' to non-scalar type `B' requested I have class A and derived from it B, but I have problems with these rows: A a(1); A *pb = new B(a); B b = *pb; //here I have an error thanks in advance for any help class A { protected: int player; public: A(int initPlayer = 0); A(const A&); A& operator=(const A&); virtual ~A(){}; virtual void foo(); void foo() const; operator int(); }; class B: public A { public: B(int initPlayer): A(initPlayer){}; ~B(){}; virtual void foo(); };

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  • What is the best way to declare a property?

    - by Simon
    Hi. We declare properties using the @property keyword and synthesize it in the implementation file. My question is, What if I declare a property using the @property keyword and also declare a variable in the interface block with the same name? For example, consider the following code, Interface: @interface myClass : NSObject { NSString *myClass_name; // LINE 1 } @property(nonatomic, retain) NSString *myClass_name; // LINE 2 @end Implementation: @implementation myClass @synthesize myClass_name // LINE 3 @end Declaring myClass_name in LINE 1 will make any problem? Like any reference problem or any unnecessary memory consumption problem?

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  • Use different Solr Similarity algo for every search

    - by snickernet
    Hi Guys, Is possible in Solr 1.4 to specify which similarity class to use for every search within a single index? Let's say, I got 2 type of search (keyword and brand). For keyword search, I want to use the DefaultSimilarity class. But, for brand search, I want to use my CustomSimilarity class. I've been modifying the schema.xml to specify a single similarity class to use. But, I came to this requirement that I have to use 2 different similarity classes. I'll be glad to here your thoughts on this. Thanks in advance.

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  • C++ - Print Out Objects From Set

    - by John Smith
    If I have a C++ set, declaration set personList; with iterator, set::const_iterator location; how can I print out the contents of the set? They are all person objects, and I have overridden the operator<< for Person. The line that errors is: cout << location and it's in a basic for loop. Netbeans gives the following error: proj.cpp:78: error: no match for ‘operator<<’ in ‘std::cout << location’ so it looks like it wants an override for the iterator's <<. Basically, I am taking objects that used to be stored in an array format, but are now in a set. What is the equivalent to cout << array[i] for sets?

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  • C++ Why is the copy constructor implicitly called?

    - by ShaChris23
    Why is the Child class's copy constructor called in the code below? I mean, it automatically converts Base to Child via the Child copy constructor. The code below compiles, but shouldn't it not compile since I haven't provided bool Child::operator!=(Base const&)? class Base { }; class Child : public Base { public: Child() {} Child(Base const& base_) : Base(base_) { std::cout <<"should never called!"; } bool operator!=(Child const&) { return true; } }; void main() { Base base; Child child; if(child != base) std::cout << "not equal"; else std::cout << "equal"; }

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  • Library for Dataflow in C

    - by msutherl
    How can I do dataflow (pipes and filters, stream processing, flow based) in C? And not with UNIX pipes. I recently came across stream.py. Streams are iterables with a pipelining mechanism to enable data-flow programming and easy parallelization. The idea is to take the output of a function that turns an iterable into another iterable and plug that as the input of another such function. While you can already do this using function composition, this package provides an elegant notation for it by overloading the operator. I would like to duplicate a simple version of this kind of functionality in C. I particularly like the overloading of the operator to avoid function composition mess. Wikipedia points to this hint from a Usenet post in 1990. Why C? Because I would like to be able to do this on microcontrollers and in C extensions for other high level languages (Max, Pd*, Python). * (ironic given that Max and Pd were written, in C, specifically for this purpose – I'm looking for something barebones)

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  • Not a statement?

    - by abelenky
    I have a simple little code fragment that is frustrating me: HashSet<long> groupUIDs = new HashSet<long>(); groupUIDs.Add(uid)? unique++ : dupes++; At compile time, it generates the error: Only assignment, call, increment, decrement, and new object expressions can be used as a statement HashSet.Add is documented to return a bool, so the ternary (?) operator should work, and this looks like a completely legitimate way to track the number of unique and duplicate items I add to a hash-set. When I reformat it as a if-then-else, it works fine. Can anyone explain the error, and if there is a way to do this as a simple ternary operator?

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  • How to search for a specific word in a row in MYSQL?

    - by user220755
    I have a row that has keywords in this way (keyword1, keyword2, keyword3) separated by commas as shown. When a user signs in, you know that he wants information about (keyword1, keyword3). Now, I have another table that has bunch of information related to different keywords, this table has a row called (keywords) which indicates if this information is suitable for which keyword. How do I render for the user the information he needs depending on the keywords. In other words, if the user wants information about (keyword3, keyword1) how do I go to the (information) table and find all the information that has the word (keyword1) or the word (keyword3) in the row (keyword)? Sorry if this is complicated (my explanation) but I tried my best to explain it. Thank you in advance :)

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  • C++ enumaration

    - by asli
    Hi,my question is about enumaration,my codes are : #include<iostream> using namespace std; int main() { enum bolumler{programcilik,donanim,muhasebe,motor,buro} bolum; bolum = donanim; cout<<bolum<<endl; bolum+=2; /* bolum=motor */ cout<<bolum; return 0; } The output should be 1 3 but according to these codes the error is: error C2676: binary '+=' : 'enum main::bolumler' does not define this operator or a conversion to a type acceptable to the predefined operator Error executing cl.exe. 111.obj - 1 error(s), 0 warning(s) Can you help me ?The other question is what can I do if I want to see the output like that "muhasebe"?

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  • What is the difference between the * and the & operators in c programming?

    - by Wesley
    I am just making sure I understand this concept correctly. With the * operator, I make a new variable, which is allocated a place in memory. So as to not unnecessarily duplicate variables and their values, the & operator is used in passing values to methods and such and it actually points to the original instance of the variable, as opposed to making new copies...Is that right? It is obviously a shallow understanding, but I just want to make sure I am not getting them mixed up. Thanks!

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  • Why does this simple bash code give a syntax error?

    - by Tim
    I have the following bash code, which is copied and pasted from "bash cookbook" (1st edition): #!/bin/bash VERBOSE=0; if [[ $1 =-v ]] then VERBOSE=1; shift; fi When I run this (bash 4.0.33), I get the following syntax error: ./test.sh: line 4: conditional binary operator expected ./test.sh: line 4: syntax error near `=-v' ./test.sh: line 4: `if [[ $1 =-v ]]' Is this as simple as a misprint in the bash cookbook, or is there a version incompatibility or something else here? What would the most obvious fix be? I've tried various combinations of changing the operator, but I'm not really familiar with bash scripting.

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  • C++ return type overload hack

    - by aaa
    I was bored and came up with such hack (pseudocode): 1 struct proxy { 2 operator int(); // int function 3 operator double(); // double function 4 proxy(arguments); 5 arguments &arguments_; 6 }; 7 8 proxy function(arguments &args) { 9 return proxy(args); 10 } 11 int v = function(...); 12 double u = function(...); is it evil to use in real code?

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  • Encrypt/ Decrypt text file in Delphi?

    - by Hemant Kothiyal
    Hi i would like to know best encryption technique for text file encryption and ecryption. My Scenario: I have software having two type of users Administartor and Operators. Our requirement is to encrypt text file when Administrator enter data using GUI and save it. That encrypted file would be input for Operator and they just need to select it and use that file. Here file should be automatically decrypt data for further calculation when Operator select those files. Please help me which encryption/ decryption technique should i use?

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  • C++ function object terminology functor, deltor, comparitor, etc..

    - by Robert S. Barnes
    Is there a commonly accepted terminology for various types for common functors? For instance I found myself naturally using comparitor for comparison functors like this: struct ciLessLibC : public std::binary_function<std::string, std::string, bool> { bool operator()(const std::string &lhs, const std::string &rhs) const { return strcasecmp(lhs.c_str(), rhs.c_str()) < 0 ? 1 : 0; } }; Or using the term deltor for something like this: struct DeleteAddrInfo { void operator()(const addr_map_t::value_type &pr) const { freeaddrinfo(pr.second); } }; If using these kinds of shorthand terms is common, it there some dictionary of them all someplace?

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  • logical or expression c++

    - by user1870181
    I have a problem using the Logical OR operator in C++. The problem is coming that the right-side expression is not evaluated if the left-side is true. I have two deque-s and I need to popLeft from them with a while, but if I can pop from the first deque, I don't pop from the second because is not evaluated, by the OR operator. How can I overcome this problem. Here is the piece of code: while( D.popLeft( k ) || E.popLeft( m ) ) { if( k < m ) { C.pushRight( k ); E.pushLeft( m ); } else { C.pushRight( m ); D.pushLeft( k ); } }

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  • Returning objects with dynamic memory

    - by Caulibrot
    I'm having trouble figuring out a way to return an object (declared locally within the function) which has dynamic memory attached to it. The problem is the destructor, which runs and deletes the dynamic memory when the object goes out of scope, i.e. when I return it and want to use the data in the memory that has been deleted! I'm doing this for an overloaded addition operator. I'm trying to do something like: MyObj operator+( const MyObj& x, const MyObj& y ) { MyObj z; // code to add x and y and store in dynamic memory of z return z; } My destructor is simply: MyObj::~MyObj() { delete [] ptr; } Any suggestions would be much appreciated!

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  • Fast comparison of char arrays?

    - by StackedCrooked
    I'm currently working in a codebase where IPv4 addresses are represented as pointers to u_int8. The equality operator is implemented like this: bool Ipv4Address::operator==(const u_int8 * inAddress) const { return (*(u_int32*) this->myBytes == *(u_int32*) inAddress); } This is probably the fasted solution, but it causes the GCC compiler warning: ipv4address.cpp:65: warning: dereferencing type-punned pointer will break strict-aliasing rules How can I rewrite the comparison correctly without breaking strict-aliasing rules and without losing performance points? I have considered using either memcmp or this macro: #define IS_EQUAL(a, b) \ (a[0] == b[0] && a[1] == b[1] && a[2] == b[2] && a[3] == b[3]) I'm thinking that the macro is the fastest solution. What do you recommend?

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  • Get top 'n' records by report_id

    - by Skudd
    I have a simple view in my MSSQL database. It consists of the following fields: report_id INT ym VARCHAR -- YYYY-MM keyword VARCHAR(MAX) visits INT I can easily get the top 10 keyword hits with the following query: SELECT TOP 10 * FROM top_keywords WHERE ym BETWEEN '2010-05' AND '2010-05' ORDER BY visits DESC Now where it gets tricky is where I have to get the top 10 records for each report_id in the given date range (ym BETWEEN @start_date AND @end_date). How would I go about getting the top 10 for each report_id? I've stumbled across suggestions involving the use of ROW_NUMBER() and RANK(), but have been vastly unsuccessful in their implementation.

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