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• Adding characters to string

  - by Jamza

  I am currently trying to build a very basic serial shell with my arduino. I am able to get an output from the device using Serial.read() and can get the character it has outputted, but I cannot work out how to then add that character to a longer to form the full command. I tried the logical thing but it doesn't work: char Command[]; void loop(){ if(Serial.available() > 0){ int clinput = Serial.read(); Command = Command + char(clinput); } Can anybody help? Thank You.

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• c++: at what point should I start using "new char[N]" vs a static buffer "char[Nmax]"

  - by dan

  My question is with regard to C++ Suppose I write a function to return a list of items to the caller. Each item has 2 logical fields: 1) an int ID, and 2) some data whose size may vary, let's say from 4 bytes up to 16Kbytes. So my question is whether to use a data structure like: struct item { int field1; char field2[MAX_LEN]; OR, rather, to allocate field2 from the heap, and require the caller to destroy when he's done: struct item{ int field1; char *field2; // new char[N] -- destroy[] when done! Since the max size of field #2 is large, is makes sense that this would be allocated from the heap, right? So once I know the size N, I call field2 = new char[N], and populate it. Now, is this horribly inefficient? Is it worse in cases where N is always small, i.e. suppose I have 10000 items that have N=4?

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• Quickest way to compute the number of shared elements between two vectors

  - by shn

  Suppose I have two vectors of the same size vector< pair<float, NodeDataID> > v1, v2; I want to compute how many elements from both v1 and v2 have the same NodeDataID. For example if v1 = {<3.7, 22>, <2.22, 64>, <1.9, 29>, <0.8, 7>}, and v2 = {<1.66, 7>, <0.03, 9>, <5.65, 64>, <4.9, 11>}, then I want to return 2 because there are two elements from v1 and v2 that share the same NodeDataIDs: 7 and 64. What is the quickest way to do that in C++ ? Just for information, note that the type NodeDataIDs is defined as I use boost as: typedef adjacency_list<setS, setS, undirectedS, NodeData, EdgeData> myGraph; typedef myGraph::vertex_descriptor NodeDataID; But it is not important since we can compare two NodeDataID using the operator == (that is, possible to do v1[i].second == v2[j].second)

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• C++ Reference of vector

  - by void

  Hello, class Refvect { public: vector<int> &refv; Refvect(int t, vector<int> &refv = vector<int>()) : refv(refv) { }; void operator()() { refv.clear(); } }; int main () { Refvect r(0); r(); } With Visual Studio 2010, this gives me an error : "vector iterators incompatible" at the execution, but I don't understand why (but I can insert elements in refv without any problem). The temporary object vector() lives as long as the reference, no?

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• The right way to implement communication between java objects

  - by imoschak

  I'm working on an academic project which simulates a rather large queuing procedure in java. The core of the simulator rests within one package where there exist 8 classes each one implementing a single concept. Every class in the project follows SRP. These classes encapsulate the behavior of the simulator and inter-connect every other class in the project. The problem that I has arisen is that most of these 8 classes are, as is logical i think, tightly coupled and each one has to have working knowledge of every other class in this package in order to be able to call methods from it when needed. The application needs only one instance of each class so it might be better to create static fields for each class in a new class and use that to make calls -instead of preserving a reference in each class for every other class in the package (which I'm certain that is incorrect)-, but is this considered a correct design solution? or is there a design pattern maybe that better suits my needs?

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• Can't compile std::map sorting, why?

  - by Vincenzo

  This is my code: map<string, int> errs; struct Compare { bool operator() (map<string, int>::const_iterator l, map<string, int>::const_iterator r) { return ((*l).second < (*r).second); } } comp; sort(errs.begin(), errs.end(), comp); Can't compile. This is what I'm getting: no matching function for call to ‘sort(..’ Why so? Can anyone help? Thanks!

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• How to check null element if it is integer array in Java?

  - by masato-san

  I'm quite new to Java and having an issue checking null element in integer array. I'm using Eclipse for editor and the line that checks null element is showing error: Line that complains: if(a[i] != null) { Error msg from Eclipse: The operator != is undefined for the argument type(s) int, null In PHP, this works without any problem but in Java it seems like I have to change the array type from integer to Object to make the line not complain (like below) Object[] a = new Object[3]; So my question is if I still want to declare as integer array and still want to check null, what is the syntax for it? Code: public void test() { int[] a = new int[3]; for(int i=0; i<a.length; i++) { if(a[i] != null) { //this line complains... System.out.println('null!'); } } }

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• Double "!!" in Ruby [closed]

  - by Alex Maslakov

  Possible Duplicate: What does !! mean in ruby? Ruby, !! operator (a/k/a the double-bang) Sometimes I see a Ruby code like this def sent? !!@sent_at end It seems to be not logical. Is it necessary to use here double !? As far as I'm concerned, it might be just def sent? @sent_at end UPDATE: then what is the difference between these def sent? !!@sent_at end def sent? @sent_at.nil? end def sent? @sent_at == nil end

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• Implementing an iterator over binary tree using C++ 11

  - by user1459339

  I would like to create an iterator over the binary tree so as to be able to use range-based for loop. I understand I ought to implement the begin() and end() function first. Begin should probably point to the root. According to the specification, however, the end() functions returns "the element following the last valid element". Which element (node) is that? Would it not be illegal to point to some "invalid" place? The other thing is the operator++. What is the best way to return "next" element in tree? I just need some advice to begin with this programming.

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• question about copy constructor

  - by lego69

  I have this class: class A { private: int player; public: A(int initPlayer = 0); A(const A&); A& operator=(const A&); ~A(); void foo() const; }; and I have function which contains this row: A *pa1 = new A(a2); can somebody please explain what exactly is going on, when I call A(a2) compiler calls copy constructor or constructor, thanks in advance

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• name of class that manipulates the entities

  - by cyberguest

  hi, i have a general question regarding naming convention. if I separate the data and operations into two separate classes. one has the data elements (entity), the other class manipulates the entity class. what do we usually call that class that manipulates the entity class? (the entity I am referring to has nothing to do with any kind of entity framework) manager? controller? operator? manipulator? thanks in advance

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• can function return 0 as reference

  - by helloWorld

  I have this snippet of the code Account& Company::findAccount(int id){ for(list<Account>::const_iterator i = listOfAccounts.begin(); i != listOfAccounts.end(); ++i){ if(i->nID == id){ return *i; } } return 0; } Is this right way to return 0 if I didn't find appropriate account? cause I receive an error: no match for 'operator!' in '!((Company*)this)->Company::findAccount(id)' I use it this way: if(!(findAccount(id))){ throw "hey"; } thanks in advance

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• Doubt regarding usage of array as a pointer in C

  - by Som

  For eg. I have an array of structs 'a' as below: struct mystruct{ int b int num; }; struct bigger_struct { struct my_struct a[10]; } struct bigger_struct *some_var; i know that the name of an array when used as a value implicitly refers to the address of the first element of the array.(Which is how the array subscript operator works at-least) Can i know do the other way around i.e if i do: some_var->a->b, it should be equivalent to some_var->a[0]->b, am i right? I have tested this and it seems to work , but is this semantically 100% correct?

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• How to get it working in O(n)?

  - by evermean

  I came across an interview task/question that really got me thinking ... so here it goes: You have an array A[N] of N numbers. You have to compose an array Output[N] such that Output[i] will be equal to multiplication of all the elements of A[N] except A[i]. For example Output[0] will be multiplication of A[1] to A[N-1] and Output[1] will be multiplication of A[0] and from A[2] to A[N-1]. Solve it without division operator and in O(n). I really tried to come up with a solution but I always end up with a complexity of O(n^2). Perhaps the is anyone smarter than me who can tell me an algorithm that works in O(n) or at least give me a hint...

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• casting a node to integer

  - by user1708762

  The code gives an error saying that "no operator matches these two operands" in the if comparison statement. I interpret,it should mean that "a node can't be converted/casted into an integer". But, the print statement prints an integer value for w[2] when used with %d format. Why is that happening? Isn't printf casting it? NODE *w=(NODE *)malloc(4*sizeof(NODE)); if(w[2]==0) printf("%d\n",w[2]); The structure of the node is- struct node{ int key; struct node *father; struct node *child[S]; int *ss; int current; };

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• Can typeid() be used to pass a function?

  - by Kerb_z

  I tried this and got the output as: void Please explain the following Code: #include <cstdio> #include <typeinfo> using namespace std ; void foo() { } int main(void) { printf("%s", typeid(foo()).name());// Please notice this line, is it same as typeid( ).name() ? return 0; } AFAIK: The typeid operator allows the type of an object to be determined at run time. So, does this sample code tell us that a function that returns void is of *type void*. I mean a function is a method and has no type. Correct?

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• Dynamic memory allocation with default values

  - by viswanathan

  class A { private: int m_nValue; public: A() { m_nValue = 0; } A(int nValue) { m_nValue = nValue); ~A() {} } Now in main if i call A a(2);// 2 will be assigned for m_nValue of object A. Now how do we do this if i want to define an array of objects. Also how do we do this if i dynamically create objects using operator new like A *pA; pA = new A[5];// while creating the object i want the parameterised constructor to be //called I hope the question is clear. Do let me know if more explanation is needed

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• partial string matching - R

  - by DonDyck

  I need to write a query in R to match partial string in column names. I am looking for something similar to LIKE operator in SQL. For e.g, if I know beginning, middle or end part of the string I would write the query in format: LIKE 'beginning%middle%' in SQL and it would return matching strings. In pmatch or grep it seems I can only specify 'beginning' , 'end' and not the order. Is there any similar function in R that I am looking for? For example, say I am looking in the vector: y<- c("I am looking for a dog", "looking for a new dog", "a dog", "I am just looking") Lets say I want to write a query which picks "looking for a new dog" and I know start of the string is "looking" and end of string is "dog". If I do a grep("dog",y) it will return 1,2,3. Is there any way I can specify beginning and end in grep?

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• What does the & sign mean in PHP?

  - by jeffkee

  I was trying to find this answer on Google but I guess the symbol & works as some operator, or is just not generally a searchable term for any reason.. anyhow. I saw this code snippet while learning how to create wordpress plugins, so I just need to know what the & means when it precedes a variable that holds a class object. //Actions and Filters if (isset($dl_pluginSeries)) { //Actions add_action('wp_head', array(&$dl_pluginSeries, 'addHeaderCode'), 1); //Filters add_filter('the_content', array(&$dl_pluginSeries, 'addContent')); }

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• use of const in c++ [closed]

  - by prp

  class X; class Y { public: Y(const X & x){cout<<"In Y"<<endl;} }; class X { public: operator Y()const{cout<<"In X"<<endl;} }; void fun(Y y) { cout<<"In fun"<<endl; } int main() { X x; fun(x); } can any one throw some light on this c++ program ...please i am new to c++

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• mySQL : using BETWEEN in table ?

  - by Meko

  I have a table that includes somestudent group name ,lesson time,day names like Schedule. I am using C# whit MYSql and I want to find which lesson is when user press button from table. I can find it like entering exact value like in table 08:30 or 10:25 , it finds. But I want to make that getting system time and checking that is it between 08:30 and 10:25 or 10:25 and 12:30 . Then I can sythat it is first lesson or it is second lesson . I have also table includes Table_Time column has 5 record like 08:20 , 10:25 , 12:20 so on. Could I use like : select Lesson_Time from mydb.clock where Lesson_Time between (current time)-30 AND (current time)+30 Or can I use between operator between two columns ? Like creating Lesson_Time_Start and Lesson_Time_End and compairing current time like Lesson_Start_Time

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• Performing an operation based on values within an array

  - by James W.

  I'm trying to figure out how to do operations based on values in an array. The values are taken from a string and inserted into the array e.g num = TextBox.Text.Split(' '); results = Convert.ToDouble(num[0]); for (int i = 0; i < num.Length - 1; i++) { if (num[i] == "+") { results += Convert.ToDouble(num[i++]); } ... } So based on this, let's say the TextBox string value was "1 + 2". So the array would be: ------------- | 1 | + | 2 | ------------- 0 1 2 (indexes) The part I'm having trouble with is Convert.ToDouble(num[i++]).. I've tried num[1] + 1, num[i + 1], etc I'm trying to figure out how to get it to perform the operation based on the first value and the value in the index after the operator. Which is the correct way to do something like this?

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• read integers from a file into a vector in C++

  - by user2922063

  I am trying to read an unknown number of double values stored on separate lines from a text file into a vector called rainfall. My code won't compile; I am getting the error no match for 'operator>>' in 'inputFile >> rainfall' for the while loop line. I understand how to read in from a file into an array, but we are required to use vectors for this project and I'm not getting it. I appreciate any tips you can give on my partial code below. vector<double> rainfall; // a vector to hold rainfall data // open file ifstream inputFile("/home/shared/data4.txt"); // test file open if (inputFile) { int count = 0; // count number of items in the file // read the elements in the file into a vector while ( inputFile >> rainfall ) { rainfall.push_back(count); ++count; } // close the file

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• Are there any javascript string formatting operations similar to the way %s is used in Python?

  - by Phil

  I've been writing a lot of javascript, and when I want to stick a variable in a string, I've been doing it like so: $("#more_info span#author").html("Created by: <a href='/user/" + author + "'>" + author + "</a>"); I feel like it's pretty ugly and a pain to write over and over. In python the %s operator makes this problem easy. Even in C, I can do sprintf (IIRC). Is there anything like that in javascript? (Lots of google'ing yielded nothing.)

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• Can't remove GPT data from MBR

  - by user2373121

  I am having difficulty getting the Ubuntu installer (and gparted) to recognize the partitions on my MBR type disk. Other operating systems and disk tools read the disk structure and the files on it fine. I have used fixparts to write a new MBR but the issue persists. I assume the issue stems from the Protective MBR data still present on the disk but I am at a loss as to how to remove it while preserving my NTFS data partition. Microsoft Windows [Version 6.1.7601] Copyright (c) 2009 Microsoft Corporation. All rights reserved. c:\Users\mike\Desktop\fixpartsfixparts 3: FixParts 0.8.8 Loading MBR data from 3: Warning: 0xEE partition doesn't start on sector 1. This can cause problems in some OSes. MBR command (? for help): Running gdisk shows Microsoft Windows [Version 6.1.7601] Copyright (c) 2009 Microsoft Corporation. All rights reserved. c:\Users\mike\Desktop\fixparts>gdisk 3: GPT fdisk (gdisk) version 0.8.7 Partition table scan: MBR: MBR only BSD: not present APM: not present GPT: not present *************************************************************** Found invalid GPT and valid MBR; converting MBR to GPT format in memory. THIS OPERATION IS POTENTIALLY DESTRUCTIVE! Exit by typing 'q' if you don't want to convert your MBR partitions to GPT format! *************************************************************** ************************************************************************ Most versions of Windows cannot boot from a GPT disk, and most varieties prior to Vista cannot read GPT disks. Therefore, you should exit now unless you understand the implications of converting MBR to GPT or creating a new GPT disk layout! ************************************************************************ Are you SURE you want to continue? (Y/N): y Command (? for help): p Disk 3:: 2930277168 sectors, 1.4 TiB Logical sector size: 512 bytes Disk identifier (GUID): BFE92CE8-F93D-4141-82B8-816AD06FB36E Partition table holds up to 128 entries First usable sector is 34, last usable sector is 2930277134 Partitions will be aligned on 2048-sector boundaries Total free space is 163846893 sectors (78.1 GiB) Number Start (sector) End (sector) Size Code Name 1 163842048 2930272255 1.3 TiB 0700 Microsoft basic data Command (? for help): r Recovery/transformation command (? for help): o Disk size is 2930277168 sectors (1.4 TiB) MBR disk identifier: 0x00000000 MBR partitions: Number Boot Start Sector End Sector Status Code 1 1 2930277167 primary 0xEE Recovery/transformation command (? for help): q

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