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• C++: Can a macro expand "abc" into 'a', 'b', 'c'?

  - by Peter Alexander

  I've written a variadic template that accepts a variable number of char parameters, i.e. template <char... Chars> struct Foo; I was just wondering if there were any macro tricks that would allow me to instantiate this with syntax similar to the following: Foo<"abc"> or Foo<SOME_MACRO("abc")> or Foo<SOME_MACRO(abc)> etc. Basically, anything that stops you from having to write the characters individually, like so Foo<'a', 'b', 'c'> This isn't a big issue for me as it's just for a toy program, but I thought I'd ask anyway.

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• Sort a list of pointers.

  - by YuppieNetworking

  Hello all, Once again I find myself failing at some really simple task in C++. Sometimes I wish I could de-learn all I know from OO in java, since my problems usually start by thinking like Java. Anyways, I have a std::list<BaseObject*> that I want to sort. Let's say that BaseObject is: class BaseObject { protected: int id; public: BaseObject(int i) : id(i) {}; virtual ~BaseObject() {}; }; I can sort the list of pointer to BaseObject with a comparator struct: struct Comparator { bool operator()(const BaseObject* o1, const BaseObject* o2) const { return o1->id < o2->id; } }; And it would look like this: std::list<BaseObject*> mylist; mylist.push_back(new BaseObject(1)); mylist.push_back(new BaseObject(2)); // ... mylist.sort(Comparator()); // intentionally omitted deletes and exception handling Until here, everything is a-ok. However, I introduced some derived classes: class Child : public BaseObject { protected: int var; public: Child(int id1, int n) : BaseObject(id1), var(n) {}; virtual ~Child() {}; }; class GrandChild : public Child { public: GrandChild(int id1, int n) : Child(id1,n) {}; virtual ~GrandChild() {}; }; So now I would like to sort following the following rules: For any Child object c and BaseObject b, b<c To compare BaseObject objects, use its ids, as before. To compare Child objects, compare its vars. If they are equal, fallback to rule 2. GrandChild objects should fallback to the Child behavior (rule 3). I initially thought that I could probably do some casts in Comparator. However, this casts away constness. Then I thought that probably I could compare typeids, but then everything looked messy and it is not even correct. How could I implement this sort, still using list<BaseObject*>::sort ? Thank you

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• please help please

  - by davit-datuashvili

  http://stackoverflow.com/questions/2836934/how-to-compare-two-char-variables please show me a few steps how to start to write this code please

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• C: using clock() to measure time in multi-threaded programs

  - by Shinka

  I've always used clock() to measure how much time my application took from start to finish, as; int main(int argc, char *argv[]) { const clock_t START = clock(); // ... const double T_ELAPSED = (double)(clock() - START) / CLOCKS_PER_SEC; } Since I've started using POSIX threads this seem to fail. It looks like clock() increases N times faster with N threads. As I don't know how many threads are going to be running simultaneously, this approach fails. So how can I measure how much time has passed ?

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• C++ String tokenisation from 3D .obj files

  - by Ben

  I'm pretty new to C++ and was looking for a good way to pull the data out of this line. A sample line that I might need to tokenise is f 11/65/11 16/70/16 17/69/17 I have a tokenisation method that splits strings into a vector as delimited by a string which may be useful static void Tokenise(const string& str, vector<string>& tokens, const string& delimiters = " ") The only way I can think of doing it is to tokenise with " " as a delimiter, remove the first item from the resulting vector, then tokenise each part by itself. Is there a good way to do this all in one?

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• About the String#substring() method

  - by alain.janinm

  If we take a look at the String#substring method implementation : new String(offset + beginIndex, endIndex - beginIndex, value); We see that a new String is created with the same original content (parameter char [] value). So the workaround is to use new String(toto.substring(...)) to drop the reference to the original char[] value and make it eligible for GC (if no more references exist). I would like to know if there is a special reason that explain this implementation. Why the method doesn't create herself the new shorter String and why she keeps the full original value instead? The other related question is : should we always use new String(...) when dealing with substring?

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• Multi-threaded random_r is slower than single threaded version.

  - by Nixuz

  The following program is essentially the same the one described here. When I run and compile the program using two threads (NTHREADS == 2), I get the following run times: real 0m14.120s user 0m25.570s sys 0m0.050s When it is run with just one thread (NTHREADS == 1), I get run times significantly better even though it is only using one core. real 0m4.705s user 0m4.660s sys 0m0.010s My system is dual core, and I know random_r is thread safe and I am pretty sure it is non-blocking. When the same program is run without random_r and a calculation of cosines and sines is used as a replacement, the dual-threaded version runs in about 1/2 the time as expected. #include <pthread.h> #include <stdlib.h> #include <stdio.h> #define NTHREADS 2 #define PRNG_BUFSZ 8 #define ITERATIONS 1000000000 void* thread_run(void* arg) { int r1, i, totalIterations = ITERATIONS / NTHREADS; for (i = 0; i < totalIterations; i++){ random_r((struct random_data*)arg, &r1); } printf("%i\n", r1); } int main(int argc, char** argv) { struct random_data* rand_states = (struct random_data*)calloc(NTHREADS, sizeof(struct random_data)); char* rand_statebufs = (char*)calloc(NTHREADS, PRNG_BUFSZ); pthread_t* thread_ids; int t = 0; thread_ids = (pthread_t*)calloc(NTHREADS, sizeof(pthread_t)); /* create threads */ for (t = 0; t < NTHREADS; t++) { initstate_r(random(), &rand_statebufs[t], PRNG_BUFSZ, &rand_states[t]); pthread_create(&thread_ids[t], NULL, &thread_run, &rand_states[t]); } for (t = 0; t < NTHREADS; t++) { pthread_join(thread_ids[t], NULL); } free(thread_ids); free(rand_states); free(rand_statebufs); } I am confused why when generating random numbers the two threaded version performs much worse than the single threaded version, considering random_r is meant to be used in multi-threaded applications.

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• Boost::asio bug in MSVC10 - Failing BOOST_WORKAROUND in ~buffer_debug_check() in buffer.hpp

  - by shaz

  A straight compilation of example http://www.boost.org/doc/libs/1_43_0/doc/html/boost_asio/tutorial/tutdaytime3/src.html results in a runtime null pointer exception. Stack trace points to the buffer_debug_check destructor which contains this comment: // MSVC's string iterator checking may crash in a std::string::iterator // object's destructor when the iterator points to an already-destroyed // std::string object, unless the iterator is cleared first. The test #if BOOST_WORKAROUND(BOOST_MSVC, = 1400) succeeds in MSVC10 and (but) results in a null pointer exception in c:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xutility line 123 _Iterator_base12& operator=(const _Iterator_base12& _Right) { // assign an iterator if (_Myproxy != _Right._Myproxy) _Adopt(_Right._Myproxy->_Mycont); return (*this); } _Right._Myproxy is NULL

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• Using sscanf to parse two strings out

  - by Jessica

  I have a semi xml formatted file that contains line with the following format: <param name="Distance" value="1000Km" /> The first char in the string is usually a TAB or spaces. I've been using the following to try to parse the two strings out (from name and value): if(sscanf(lineread, "\t<param name=\"%s\" value=\"%s\" />", name, value) == 1) { //do something } name and value are char* Now, the result is always the same: name gets parse (I need to remove the quotes) and name is always empty. What am I doing wrong? Thanks, code is appreciated. Jess.

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• Internal class and access to external members.

  - by Knowing me knowing you

  I have question with this same title here but now as I'll present in code below this seems to behave in the opposite way to the way explained to me in my first question with the same title. Ok code: class LINT_rep { private: char* my_data_; //stores separately every single digit from a number public: class Iterator:public iterator<bidirectional_operator_tag,char*> { Iterator(const LINT_rep&); }; }; #include "StdAfx.h" #include "LINT_rep.h" LINT_rep::Iterator::Iterator(const LINT_rep& owner):myData_(nullptr) { myData_ = owner.my_data_; /* HERE I'M ACCESSING my_data WHICH IS PRIVATE AND THIS CODE COMPILES ON VS2010 ULTIMATE BUT IT SHOULDN'T BECAUSE my_data IS PRIVATE AND OTHER CLASS SHOULDN'T HAVE ACCESS TO IT'S PRIVATE MEMB. AS EXPLAINED TO ME IN QUESTION TO WHICH I;VE PROVIDED LINK. */ } Question in the code. Thanks.

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• Is concatenating with an empty string to do a string conversion really that bad?

  - by polygenelubricants

  Let's say I have two char variables, and later on I want to concatenate them into a string. This is how I would do it: char c1, c2; // ... String s = "" + c1 + c2; I've seen people who say that the "" + "trick" is "ugly", etc, and that you should use String.valueOf or Character.toString instead. I prefer this construct because: I prefer using language feature instead of API call if possible In general, isn't the language usually more stable than the API? If language feature only hides API call, then even stronger reason to prefer it! More abstract! Hiding is good! I like that the c1 and c2 are visually on the same level String.valueOf(c1) + c2 suggests something is special about c1 It's shorter. Is there really a good argument why String.valueOf or Character.toString is preferrable to "" +? Trivia: in java.lang.AssertionError, the following line appears 7 times, each with a different type: this("" + detailMessage);

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• NSNotifications vs delegate for multiple instances of same protocol

  - by Brent Traut

  I could use some architectural advice. I've run into the following problem a few times now and I've never found a truly elegant way to solve it. The issue, described at the highest level possible:I have a parent class that would like to act as the delegate for multiple children (all using the same protocol), but when the children call methods on the parent, the parent no longer knows which child is making the call. I would like to use loose coupling (delegates/protocols or notifications) rather than direct calls. I don't need multiple handlers, so notifications seem like they might be overkill. To illustrate the problem, let me try a super-simplified example: I start with a parent view controller (and corresponding view). I create three child views and insert each of them into the parent view. I would like the parent view controller to be notified whenever the user touches one of the children. There are a few options to notify the parent: Define a protocol. The parent implements the protocol and sets itself as the delegate to each of the children. When the user touches a child view, its view controller calls its delegate (the parent). In this case, the parent is notified that a view is touched, but it doesn't know which one. Not good enough. Same as #1, but define the methods in the protocol to also pass some sort of identifier. When the child tells its delegate that it was touched, it also passes a pointer to itself. This way, the parent know exactly which view was touched. It just seems really strange for an object to pass a reference to itself. Use NSNotifications. The parent defines a separate method for each of the three children and then subscribes to the "viewWasTouched" notification for each of the three children as the notification sender. The children don't need to attach themselves to the user dictionary, but they do need to send the notification with a pointer to themselves as the scope. Same as #4, but rather than using separate methods, the parent could just use one with a switch case or other branching along with the notification's sender to determine which path to take. Create multiple man-in-the-middle classes that act as the delegates to the child views and then call methods on the parent either with a pointer to the child or with some other differentiating factor. This approach doesn't seem scalable. Are any of these approaches considered best practice? I can't say for sure, but it feels like I'm missing something more obvious/elegant.

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• What am I encrypting wrong here?

  - by Katie Krueger

  So I have a wordplay project to do and I have to encrypt some characters. I am at the point where I am stuck, and when I run it and type 1 for encrypt it doesn't shift that many letters. It just prints the work over again. I am wondering what I could do to fix it where if I say "hello" it will print 1 character over and say "ifmmp" Thank you! import java.util.Scanner; public class WordPlayTester{ public static void main(String [] args){ String word, reverse=""; String original; int key= 0; String Menu= "1-Encrypt \n2-Decrypt \n3-Is Palindrome \n0-Quit \n-Select an option-"; Scanner in = new Scanner(System.in); System.out.println("-Type any word-"); word = in.nextLine(); System.out.println(Menu); int choice=in.nextInt(); if(choice==1) { System.out.println("Insert a Key number"); int select= in.nextInt(); for (int i=0; i < word.length(); i++) { char c = word.charAt(i); if (c >= 'A' && c <= 'Z') { c = (char)(c - 64); int n = c+1; n = n % 26; if (n < 0) { n = n + 26; } c = (char)(n + 65); } System.out.println(c); } } else if(choice==3) { int length = word.length(); for ( int i = length - 1 ; i >= 0 ; i-- ) reverse = reverse + word.charAt(i); if (word.equals(reverse)) System.out.println("Your word is a palindrome."); else System.out.println("Your word is not a palindrome."); } else if(choice==0) { System.exit(0); } else { System.out.println(Menu); } } }

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• Get current session /process id from inside a mysql query

  - by Indra Ginanjar

  I'm trying to create a table for pseudo array variable. That looks like CREATE TABLE IF NOT EXISTS `MyArray`.`ArrayTable` ( `ID` INT UNSIGNED NOT NULL COMMENT 'Hash value of SessionID + ArrayName' , `SessionID` INT UNSIGNED NOT NULL , `ArrayName` CHAR(26) NOT NULL COMMENT '32 digit char - 6 digit longest process id (assumtion)' , `Index` INT UNSIGNED NOT NULL , `Value` TEXT NOT NULL , PRIMARY KEY (`ID`, `SessionID`) ) ENGINE = MyISAM; The table is not normalized yet, 'hope this will make it a little simpler to understand :) To avoid collission between client, there should be a differentiator between client session. For that reason i think need to know current session/process id (just like "SHOW PROCESSLIST") but really need to know IN WHICH process the query are?

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• Storing a NTFS Security Descriptor in C

  - by Doori Bar

  My goal is to store a NTFS Security Descriptor in its identical native state. The purpose is to restore it on-demand. I managed to write the code for that purpose, I was wondering if anybody mind to validate a sample of it? (The for loop represents the way I store the native descriptor) This sample only contains the flag for "OWNER", but my intention is to apply the same method for all of the security descriptor flags. I'm just a beginner, would appreciate the heads up. Thanks, Doori Bar #define _WIN32_WINNT 0x0501 #define WINVER 0x0501 #include <stdio.h> #include <windows.h> #include "accctrl.h" #include "aclapi.h" #include "sddl.h" int main (void) { DWORD lasterror; PSECURITY_DESCRIPTOR PSecurityD1, PSecurityD2; HANDLE hFile; PSID owner; LPTSTR ownerstr; BOOL ownerdefault; int ret = 0; unsigned int i; hFile = CreateFile("c:\\boot.ini", GENERIC_READ | ACCESS_SYSTEM_SECURITY, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL); if (hFile == INVALID_HANDLE_VALUE) { fprintf(stderr,"CreateFile() failed. Error: INVALID_HANDLE_VALUE\n"); return 1; } lasterror = GetSecurityInfo(hFile, SE_FILE_OBJECT, OWNER_SECURITY_INFORMATION , &owner, NULL, NULL, NULL, &PSecurityD1); if (lasterror != ERROR_SUCCESS) { fprintf(stderr,"GetSecurityInfo() failed. Error: %lu;\n", lasterror); ret = 1; goto ret1; } ConvertSidToStringSid(owner,&ownerstr); printf("ownerstr of PSecurityD1: %s\n", ownerstr); /* The for loop represents the way I store the native descriptor */ PSecurityD2 = malloc( GetSecurityDescriptorLength(PSecurityD1) * sizeof(unsigned char) ); for (i=0; i < GetSecurityDescriptorLength(PSecurityD1); i++) ((unsigned char *) PSecurityD2)[i] = ((unsigned char *) PSecurityD1)[i]; if (IsValidSecurityDescriptor(PSecurityD2) == 0) { fprintf(stderr,"IsValidSecurityDescriptor(PSecurityD2) failed.\n"); ret = 2; goto ret2; } if (GetSecurityDescriptorOwner(PSecurityD2,&owner,&ownerdefault) == 0) { fprintf(stderr,"GetSecurityDescriptorOwner() failed."); ret = 2; goto ret2; } ConvertSidToStringSid(owner,&ownerstr); printf("ownerstr of PSecurityD2: %s\n", ownerstr); ret2: free(owner); free(ownerstr); free(PSecurityD1); free(PSecurityD2); ret1: CloseHandle(hFile); return ret; }

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• delete & new in c++

  - by singh

  Hi This may be very simple question,But please help me. i wanted to know what exactly happens when i call new & delete , For example in below code char * ptr=new char [10]; delete [] ptr; call to new returns me memory address. Does it allocate exact 10 bytes on heap, Where information about size is stored.When i call delete on same pointer,i see in debugger that there are a lot of byte get changed before and after the 10 Bytes. Is there any header for each new which contain information about number of byte allocated by new. Thanks a lot

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• recv receiving not whole data sometime

  - by milo

  hi all, i have following issue: here is the chunk of code: void get_all_buf(int sock, std::string & inStr) { int n = 1; char c; char temp[1024*1024]; bzero(temp, sizeof(temp)); n = recv(sock, temp, sizeof(temp), 0); inStr = temp; }; but sometimes recv returning not whole data (data length always less then sizeof(temp)), only it's part. write side always sends me whole data (i got it with sniffer). what matter? thx. P.S. i know, good manner suggests me to check n (if (n < 0) perror ("error while receiving data), but it doesn't matter now - it's not reason of my problem. P.S.2 i've forgot - it's blocking socket.

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• Passing enums to functions in C++

  - by rocknroll

  Hi all, I have a header file with all the enums listed (#ifndef #define #endif construct has been used to avoid multiple inclusion of the file) that I use in multiple cpp files in my application.One of the enums in the files is enum StatusSubsystem {ENABLED,INCORRECT_FRAME,INVALID_DATA,DISABLED}; There are functions in the application delcared as ShowStatus(const StatusSubsystem&); Earlier in the application when I made calls to the above function like ShowStatus(INCORRECT_FRAME); my application used to compile perfectly. But after some code was added The compilation halts giving the following error: File.cpp:71: error: invalid conversion from `int' to `StatusSubsystem' File.cpp:71: error: initializing argument 1 of `void Class::ShowStatus(const StatusSubsystem&) I checked the code for any conflicting enums in the new code and it looked fine. My Question is what is wrong with the function call that compiler shows as erroneous? For your reference the function definition is: void Class::ShowStatus(const StatusSubsystem& eStatus) { QPalette palette; mStatus=eStatus;//store current Communication status of system if(eStatus==DISABLED) { //select red color for label, if it is to be shown disabled palette.setColor(QPalette::Window,QColor(Qt::red)); mLabel->setText("SYSTEM"); } else if(eStatus==ENABLED) { //select green color for label,if it is to be shown enabled palette.setColor(QPalette::Window,QColor(Qt::green)); mLabel->setText("SYSTEM"); } else if(eStatus==INCORRECT_FRAME) { //select yellow color for label,to show that it is sending incorrect frames palette.setColor(QPalette::Window,QColor(Qt::yellow)); mLabel->setText("SYSTEM(I)"); } //Set the color on the Label mLabel->setPalette(palette); } A strange side effect of this situation is it compiles when I cast all the calls to ShowStatus() as ShowStatus((StatusSubsystem)INCORRECT_FRAME); Though this removes any compilation error, but a strange thing happens. Though I make call to INCORRECT_FRAME above but in function definition it matches with ENABLED. How on earth is that possible? Its like while passing INCORRECT_FRAME by reference, it magically converts to ENABLED, which should be impossible. This is driving me nuts. Can you find any flaw in what I am doing? or is it something else? The application is made using C++,Qt-4.2.1 on RHEL4. Thanks.

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• Same loop giving different output. Java IO

  - by Nitesh Panchal

  Hi, I am facing a very strange problem where the same loop keeps giving me different different output on change of value of BUFFER final int BUFFER = 100; char[] charArr = new char[BUFFER]; StringBuffer objStringBuffer = new StringBuffer(); while (objBufferedReader.read(charArr, 0,BUFFER) != -1) { objStringBuffer.append(charArr); } objFileWriter.write(objStringBuffer.toString()); When i change BUFFER size to 500 it gives me a file of 7 kb when i change BUFFER size to 100000 it gives a file of 400 kb where the contents are repeated again and again. Please help. What should i do to prevent this?

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• C++ operator overloading doubt

  - by avd

  I have a code base, in which for Matrix class, these two definitions are there for () operator: template <class T> T& Matrix<T>::operator() (unsigned row, unsigned col) { ...... } template <class T> T Matrix<T>::operator() (unsigned row, unsigned col) const { ...... } One thing I understand is that the second one does not return the reference but what does const mean in the second declaration. Also which function is called when I do say mat(i,j)

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• Javascript pass reference by value

  - by Carlos R. Batista

  Im having this weird reference issue when im trying to get a JSON file through query: var themeData; $.getJSON("json/sample.js", function(data) { themeData = data.theme; console.log(themeData.sample[0].description); }); console.log(themeData.sample[0].description); The first console.log works, the second doesnt. Im guessing because "data" already expired by the time the script gets there and themeData is just a mere pointer to "data". Is there a ways I can make sure themeData gets a duplicate of "data" and not just a pointer to it?

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• Why this works (Templates, SFINAE). C++

  - by atch

  Hi guys, reffering to yesterday's post, this woke me up this morning. Why this actually works? As long as the fnc test is concerned this fnc has no body so how can perform anything? Why and how this works? I'm REALLY interested to see your answers. template<typename T> class IsClassT { private: typedef char One; typedef struct { char a[2]; } Two; template<typename C> static One test(int C::*); //NO BODY HERE template<typename C> static Two test(…); //NOR HERE public: enum { Yes = sizeof(IsClassT<T>::test<T>(0)) == 1 }; enum { No = !Yes }; }; Thanks in advance with help to understand this very interesting fenomena.

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• C++ : Initializing base class constant static variable with different value in derived class ?

  - by chmike

  I have a base class A with a constant static variable a. I need that instances of class B have a different value for the static variable a. How could this be achieved, preferably with static initialization ? class A { public: static const int a; }; const int A::a = 1; class B : public A { // ??? // How to set *a* to a value specific to instances of class B ? };

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• Operator Overloading for Queue C++

  - by Josh

  I was trying to use the overload operator method to copy the entries of one queue into another, but I am going wrong with my function. I don't know how else to access the values of the queue "original" any other way than what I have below: struct Node { int item; Node* next; }; class Queue { public: [...] //Extra code here void operator = (const Queue &original); protected: Node *front, *end; } void Queue::operator=(const Queue &original) { //THIS IS WHERE IM GOING WRONG while(original.front->next != NULL) { front->item = original.front->item; front->next = new Node; front = front->next; original.front = original.front->next; } }

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• I don't get this C/C++ Joke

  - by Buttercup

  After reading this article on thedailywtf.com, I'm not sure that I really got the joke. It says there that some guy changed the code from int function() { int x; char data_string[15]; ... x = 2; strcpy(data_string,"data data data"); ... } to int function() { int x = 2; char data_string[15] = "data data data"; ... } everywhere in the code and that for some reason did inflate the size of the executable from 1 to 2 CDs (or maybe it didn't do that?). Obviously I'm not familiar enough with C/C++ to get this joke, but what seems strangest is that the 2nd code listing seems "cleaner"—at least from what I've been told in school (that is that initializing variables is a good thing, not a bad one).

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