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• parsing of mathematical expressions

  - by gcc

  (in c90) (linux) input: sqrt(2 - sin(3*A/B)^2.5) + 0.5*(C*~(D) + 3.11 +B) a b /*there are values for a,b,c,d */ c d input: cos(2 - asin(3*A/B)^2.5) +cos(0.5*(C*~(D)) + 3.11 +B) a b /*there are values for a,b,c,d */ c d input: sqrt(2 - sin(3*A/B)^2.5)/(0.5*(C*~(D)) + sin(3.11) +ln(B)) /*max lenght of formula is 250 characters*/ a b /*there are values for a,b,c,d */ c /*each variable with set of floating numbers*/ d As you can see infix formula in the input depends on user. My program will take a formula and n-tuples value. Then it calculate the results for each value of a,b,c and d. If you wonder I am saying ;outcome of program is graph. /sometimes,I think i will take input and store in string. then another idea is arise " I should store formula in the struct" but i don't know how I can construct the code on the base of structure./ really, I don't know way how to store the formula in program code so that I can do my job. can you show me? /* a,b,c,d is letters cos,sin,sqrt,ln is function*/

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• C programing fopen

  - by Pedro

  #include <stdio.h> #include <stdlib.h> typedef struct aluno{ char cabecalho[60]; char info[100]; int n_alunos; char dados[100]; char curso[100]; int numero; char nome[100]; char e_mail[100]; int n_disciplinas; int nota; }ALUNO; void cabclh(ALUNO alunos[],int a){ FILE *fp; int i; for(i=0;i<100;i++){ fp=fopen("trabalho.txt","r"); } if(fp==NULL){ printf("Erro ao abrir o ficheiro\n"); } while(!feof(fp)){ fgets(alunos[i].cabecalho,100,fp); printf("%s\n",alunos[i].cabecalho); } } fclose(fp); } what is wrong here? main: int main(int argc, char *argv[]){ ALUNO alunos[100]; int aluno; int b; cabclh(aluno,b); system("PAUSE"); return 0

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• Strange results while measuring delta time on Linux

  - by pachanga

  Folks, could you please explain why I'm getting very strange results from time to time using the the following code: #include <unistd.h> #include <sys/time.h> #include <time.h> #include <stdio.h> int main() { struct timeval start, end; long mtime, seconds, useconds; while(1) { gettimeofday(&start, NULL); usleep(2000); gettimeofday(&end, NULL); seconds = end.tv_sec - start.tv_sec; useconds = end.tv_usec - start.tv_usec; mtime = ((seconds) * 1000 + useconds/1000.0) + 0.5; if(mtime > 10) printf("WTF: %ld\n", mtime); } return 0; } (You can compile and run it with: gcc test.c -o out -lrt && ./out) What I'm experiencing is sporadic big values of mtime variable almost every second or even more often, e.g: $ gcc test.c -o out -lrt && ./out WTF: 14 WTF: 11 WTF: 11 WTF: 11 WTF: 14 WTF: 13 WTF: 13 WTF: 11 WTF: 16 How can this be possible? Is it OS to blame? Does it do too much context switching? But my box is idle( load average: 0.02, 0.02, 0.3). Here is my Linux kernel version: $ uname -a Linux kurluka 2.6.31-21-generic #59-Ubuntu SMP Wed Mar 24 07:28:56 UTC 2010 i686 GNU/Linux

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• C++ Constructor With Parameters Won't Initialize, Errors C2059 and C2228

  - by Some Girl

  I'm a C# programmer trying to muddle through C++ to create a Windows Forms Application. I have a Windows Form that makes use of a user-created class. Basically I'm trying to use a constructor that takes parameters, but my form won't let me initialize the object with parameter. Here's the code, hopefully somebody can explain the problem to me because I'm completely baffled... Here's my header file: BankAcct.h public ref class BankAcct { private: int money; public: BankAcct(); BankAcct(int); void Deposit(int); void GetBalance(int&); }; And my definition file: BankAcct.cpp #include "StdAfx.h" #include "BankAcct.h" BankAcct::BankAcct() { money = 0; } BankAcct::BankAcct(int startAmt) { money = startAmt; } void BankAcct::Deposit(int depAmt) { money += depAmt; } void BankAcct::GetBalance(int& balance) { balance = money; } And finally my main form. Won't copy the whole thing, of course, but I'm trying to declare the new bank account object, and start it with a balance of say $50. private: BankAcct myAccount(50); //does not work! WHY?? //private: //BankAcct myAccount; //works then in the form constructor my code is this: public: frmBank(void) { InitializeComponent(); int bal; myAccount.GetBalance(bal); lblBankBalance->Text += Convert::ToString(bal); } I've included the BankAcct.h file at the top of my frmBank.h, what else am I doing wrong here? It works great if I use the default constructor (the one that starts the bank balance at zero). I get the following error messages: error C2059: syntax error: 'constant' and error C2228: left of '.GetBalance' must have class/struct/union Thank you for any and all help on this one!!

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• C# Convert string to nullable type (int, double, etc...)

  - by Nathan Koop

  I am attempting to do some data conversion. Unfortunately, much of the data is in strings, where it should be int's or double, etc... So what I've got is something like: double? amount = Convert.ToDouble(strAmount); The problem with this approach is if strAmount is empty, if it's empty I want it to amount to be null, so when I add it into the database the column will be null. So I ended up writing this: double? amount = null; if(strAmount.Trim().Length>0) { amount = Convert.ToDouble(strAmount); } Now this works fine, but I now have five lines of code instead of one. This makes things a little more difficult to read, especially when I have a large amount of columns to convert. I thought I'd use an extension to the string class and generic's to pass in the type, this is because it could be a double, or an int, or a long. So I tried this: public static class GenericExtension { public static Nullable<T> ConvertToNullable<T>(this string s, T type) where T: struct { if (s.Trim().Length > 0) { return (Nullable<T>)s; } return null; } } But I get the error: Cannot convert type 'string' to 'T?' Is there a way around this? I am not very familiar with creating methods using generics.

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• how to emulate thread local storage at user space in C++ ?

  - by vprajan

  I am working on a mobile platform over Nucleus RTOS. It uses Nucleus Threading system but it doesn't have support for explicit thread local storage i.e, TlsAlloc, TlsSetValue, TlsGetValue, TlsFree APIs. The platform doesn't have user space pthreads as well. I found that __thread storage modifier is present in most of the C++ compilers. But i don't know how to make it work for my kind of usage. How does __thread keyword can be mapped with explicit thread local storage? I read many articles but nothing is so clear for giving me the following basic information will __thread variable different for each thread ? How to write to that and read from it ? does each thread has exactly one copy of the variable ? following is the pthread based implementation: pthread_key_t m_key; struct Data : Noncopyable { Data(T* value, void* owner) : value(value), owner(owner) {} int* value; }; inline ThreadSpecific() { int error = pthread_key_create(&m_key, destroy); if (error) CRASH(); } inline ~ThreadSpecific() { pthread_key_delete(m_key); // Does not invoke destructor functions. } inline T* get() { Data* data = static_cast<Data*>(pthread_getspecific(m_key)); return data ? data->value : 0; } inline void set(T* ptr) { ASSERT(!get()); pthread_setspecific(m_key, new Data(ptr, this)); } How to make the above code use __thread way to set & get specific value ? where/when does the create & delete happen? If this is not possible, how to write custom pthread_setspecific, pthread_getspecific kind of APIs. I tried using a C++ global map and index it uniquely for each thread and retrieved data from it. But it didn't work well.

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• C++ Dynamic Allocation Mismatch: Is this problematic?

  - by acanaday

  I have been assigned to work on some legacy C++ code in MFC. One of the things I am finding all over the place are allocations like the following: struct Point { float x,y,z; }; ... void someFunc( void ) { int numPoints = ...; Point* pArray = (Point*)new BYTE[ numPoints * sizeof(Point) ]; ... //do some stuff with points ... delete [] pArray; } I realize that this code is atrociously wrong on so many levels (C-style cast, using new like malloc, confusing, etc). I also realize that if Point had defined a constructor it would not be called and weird things would happen at delete [] if a destructor had been defined. Question: I am in the process of fixing these occurrences wherever they appear as a matter of course. However, I have never seen anything like this before and it has got me wondering. Does this code have the potential to cause memory leaks/corruption as it stands currently (no constructor/destructor, but with pointer type mismatch) or is it safe as long as the array just contains structs/primitive types?

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• HashMap Memory Leak because of Dynamic Array

  - by Jake M

  I am attempting to create my own HashMap to understand how they work. I am using an array of Linked Lists to store the values(strings) in my hashmap. I am creating the array like this: Node** list; Instead of this: Node* list[nSize]; This is so the array can be any size at runtime. But I think I am getting a memory leak because of how I am doing this. I dont know where the error is but when I run the following simple code the .exe crashes. Why is my application crashing and how can I fix it? Note: I am aware that using a vector would be much better than an array but this is just for learning and I want to challenge myself to create the hashmap using a 'Dynamic' Array. PS: is that the correct term(Dynamic Array) for the kind of array I am using? struct Node { // to implement }; class HashMap { public: HashMap(int dynSize) { *list = new Node[dynSize]; size = dynSize; for (int i=0; i<size; i++) list[i] = NULL; cout << "END\n"; } ~HashMap() { for (int i=0; i<size; i++) delete list[i]; } private: Node** list; // I could use a vector here but I am experimenting with a pointer to an array(pointer), also its more elegant int size; }; int main() { // When I run this application it crashes. Where is my memory leak? HashMap h(5); system("PAUSE"); return 0; }

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• How to compare two structure strings in C++

  - by Arvandor

  Ok, so this week in class we're working with arrays. I've got an assignment that wanted me to create a structure for an employee containing an employee ID, first name, last name, and wages. Then it has me ask users for input for 5 different employees all stored in an array of this structure, then ask them for a search field type, then a search value. Lastly, display all the information for all positive search results. I'm still new, so I'm sure it isn't a terribly elegant program, but what I'm trying to do now is figure out how to compare a user entered string with the string stored in the structure... I'll try to give all the pertinent code below. struct employee { int empid, string firstname, string lastname, float wage }; employee emparray[] = {}; employee value[] = {}; //Code for populating emparray and structure, then determine search field etc. cout << "Enter a search value: "; cin >> value.lastname; for(i = 0; i < 5; i++) { if(strcmp(value.lastname.c_str, emparray[i].lastname.c_str) == 0) { output(); } } Which... I thought would work, but it's giving me the following error.. Error 1 error C3867: 'std::basic_string<_Elem,_Traits,_Alloc>::c_str': function call missing argument list; use '&std::basic_string<_Elem,_Traits,_Alloc>::c_str' to create a pointer to member d:\myfile Any thoughts on what's going on? Is there a way to compare two .name notated strings without totally revamping the program? IF you want to drill me on best practices, please feel free, but also please try to solve my particular problem.

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• Garbage data from serial port.

  - by sasayins

  Hi I wrote a code in Linux platform that read the data in serial port, my code below: int fd; char *rbuff=NULL; struct termios new_opt, old_opt; int ret; fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY); if( fd == -1 ) { printf("Can't open file: %s\n", strerror(errno)); return -1; } tcgetattr(fd, &old_opt); new_opt.c_cflag = B115200 | CS8 | CLOCAL | CREAD; new_opt.c_iflag = IGNPAR /*| ICRNL*/; new_opt.c_oflag = 0; new_opt.c_lflag = ICANON; tcsetattr(fd, TCSANOW, &new_opt); rbuff = malloc(NBUFF); printf("reading..\n"); memset(rbuff,0x00,NBUFF); ret = read(fd, rbuff, NBUFF); printf("value:%s",rbuff); if(ret == -1) { printf("Read error:%s\n",strerror(errno)); return -1; } tcsetattr(fd, TCSANOW, &old_opt); close(fd); My problem is the code above doesn't read the first data that was transmitted, then the second transmission the data is garbage, then the third is the normal data. Did I missed a setting in the serial port? Thanks.

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• kernel get stack when signalled

  - by yoavstr

  hi there i write readers and writers where the kernel have to syncronize between them and block writer who already read a massage when i am in the queue waiting I get signal so I do the fallowing while (i_Allready_Read(myf) == ALLREADY_READ || isExistWriter == false ) //while (!(i_Allready_Read(aliveProc,current->pid))) { int i, is_sig = 0; printk(KERN_INFO "\n\n*****entered set in read ******\n\n" ); if (i_Allready_Read(myf) == ALLREADY_READ ) wait_event_interruptible (readWaitQ1, !i_Allready_Read(myf)); else wait_event_interruptible (readWaitQ1, isExistWriter); //printk(KERN_INFO "Read Wakeup %d\n",current->pid); for (i = 0; i < _NSIG_WORDS && !is_sig; i++) { is_sig = current->pending.signal.sig[i] & ~current->blocked.sig[i]; } if (is_sig) { handledClose(myf); module_put (THIS_MODULE); return -EINTR; } } return 0;//success } inline void handledClose(struct file *myf)//v { /* *if we close the writer other writer *would be able to enter to permissiones */ if (myf == writerpid ) { isExistWriter = DOESNT_EXIST; //printk(KERN_INFO "procfs_close : this is pid that just closed %d \n", writerpid); } /* *else its a reader so our numofreaders *need to decremented */ else { removeFromArr(myf); numOfReaders--; } } and my close does nothing ... what did i do wrong?

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• how to Clean up(destructor) a dynamic Array of pointers??

  - by Ahmed Sharara

  Is that Destructor is enough or do I have to iterate to delete the new nodes?? #include "stdafx.h" #include<iostream> using namespace std; struct node{ int row; int col; int value; node* next_in_row; node* next_in_col; }; class MultiLinkedListSparseArray { private: char *logfile; node** rowPtr; node** colPtr; // used in constructor node* find_node(node* out); node* ins_node(node* ins,int col); node* in_node(node* ins,node* z); node* get(node* in,int row,int col); bool exist(node* so,int row,int col); //add anything you need public: MultiLinkedListSparseArray(int rows, int cols); ~MultiLinkedListSparseArray(); void setCell(int row, int col, int value); int getCell(int row, int col); void display(); void log(char *s); void dump(); }; MultiLinkedListSparseArray::MultiLinkedListSparseArray(int rows,int cols){ rowPtr=new node* [rows+1]; colPtr=new node* [cols+1]; for(int n=0;n<=rows;n++) rowPtr[n]=NULL; for(int i=0;i<=cols;i++) colPtr[i]=NULL; } MultiLinkedListSparseArray::~MultiLinkedListSparseArray(){ // is that destructor enough?? cout<<"array is deleted"<<endl; delete [] rowPtr; delete [] colPtr; }

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• MATLAB: svds() not converging

  - by Paul

  So using MATLAB's svds() function on some input data as such: [U, S, V, flag] = svds(data, nSVDs, 'L') I noticed that from run to run with the same data, I'd get drastically different output SVD sizes from run to run. When I checked whether 'flag' was set, I found that it was, indicating that the SVDs had not converged. My normal system here would be that if it really needs to converge, I'd do something like this: flag = 1 svdOpts = struct('tol', 1e-10, 'maxit', 600, 'disp', 0); while flag: if svdOpts.maxit > 1e6 error('There''s a real problem here.') end [U, S, V, flag] = svds(data, nSVDs, 'L', svdOpts) svdOpts.maxit = svdOpts.maxit*2 end But from what I can tell, when you use 'L' as the third argument, the fourth argument is ignored, meaning I just have to deal with the fact that it's not converging? I'm not even really sure how to use the 'sigma' argument in place of the 'L' argument. I've also tried reducing the number of SVDs calculated to no avail. Any help on this matter would be much appreciated. EDIT While following up on the comments below, I found that the problem had to do with the way I was building my data matrices. Turned out I had accidentally inverted a matrix and had an input of size (4000x1) rather than (20x200), which was what was refusing to converge. I also did some more timing tets and found that the fourth argument was not, in fact, being ignored, so that's on me. Thanks for the help guys.

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• Compile time type determination in C++

  - by dicroce

  A coworker recently showed me some code that he found online. It appears to allow compile time determination of whether a type has an "is a" relationship with another type. I think this is totally awesome, but I have to admit that I'm clueless as to how this actually works. Can anyone explain this to me? template<typename BaseT, typename DerivedT> inline bool isRelated(const DerivedT&) { DerivedT derived(); char test(const BaseT&); // sizeof(test()) == sizeof(char) char (&test(...))[2]; // sizeof(test()) == sizeof(char[2]) struct conversion { enum { exists = (sizeof(test(derived())) == sizeof(char)) }; }; return conversion::exists; } Once this function is defined, you can use it like this: #include <iostream> class base {}; class derived : public base {}; class unrelated {}; int main() { base b; derived d; unrelated u; if( isRelated<base>( b ) ) std::cout << "b is related to base" << std::endl; if( isRelated<base>( d ) ) std::cout << "d is related to base" << std::endl; if( !isRelated<base>( u ) ) std::cout << "u is not related to base" << std::endl; }

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• Image processing: smart solution for converting superixel (128x128 pixel) coordinates needed

  - by zhengtonic

  Hi, i am searching for a smart solution for this problem: A cancer ct picture is stored inside a unsigned short array (1-dimensional). I have the location information of the cancer region inside the picture, but the coordinates (x,y) are in superpixel (128x128 unsigned short). My task is to highlight this region. I already solved this one by converting superpixel coordinates into a offset a can use for the unsigned short array. It works fine but i wonder if there is a smarter way to solve this problem, since my solution needs 3 nested for-loops. Is it possible to access the ushort array "superpixelwise", so i can navigate the ushort array in superpixels. ... // i know this does no work ... just to give you an idea what i was thinking of ... typedef struct { unsigned short[128x128] } spix; spix *spixptr; unsigned short * bufptr = img->getBuf(); spixptr = bufptr; ... best regards, zhengtonic

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• C++ Serial Port Only Responding Once Using Write()

  - by Pfeffer

  All the code below works. My device responds, C,7 is a reset. When I run this the second time it doesn't respond. If I manually turn my device off and on, then run this script again it works. But not if I press the button to run the script the second time. RS232: 57600,8,N,1 Any ideas?? Is there any more information needed to solve this? *Also when I get this working I'm going to have to use the read() function to get the devices responses. Does anyone know the correct format I need to use, based on the below code? Sorry I'm new to C++...I'm more of a PHP guy. *I also don't know if 1024 is right, but it seems to work so eh... Thanks so much! #include <termios.h> int fd; struct termios options; fd=open("/dev/tty.KeySerial1", O_RDWR | O_NOCTTY | O_NDELAY); fcntl(fd, F_SETFL, 0); tcgetattr(fd,&options); options.c_ispeed=57600; options.c_ospeed=57600; options.c_cflag |= (CLOCAL | CREAD); options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG); options.c_cflag &= ~CSTOPB; options.c_lflag &= ~ECHO; options.c_oflag &= ~ECHO; options.c_oflag &= ~OPOST; options.c_cflag |= CS8; options.c_cflag |= CRTSCTS; options.c_cc[VMIN] = 0; options.c_cc[VTIME] =10; tcflush(fd, TCIFLUSH); tcsetattr(fd,TCSANOW,&options); write(fd, "C,7\r\n", 1024); close(fd);

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• Can g++ fill uninitialized POD variables with known values?

  - by Bob Lied

  I know that Visual Studio under debugging options will fill memory with a known value. Does g++ (any version, but gcc 4.1.2 is most interesting) have any options that would fill an uninitialized local POD structure with recognizable values? struct something{ int a; int b; }; void foo() { something uninitialized; bar(uninitialized.b); } I expect uninitialized.b to be unpredictable randomness; clearly a bug and easily found if optimization and warnings are turned on. But compiled with -g only, no warning. A colleague had a case where code similar to this worked because it coincidentally had a valid value; when the compiler upgraded, it started failing. He thought it was because the new compiler was inserting known values into the structure (much the way that VS fills 0xCC). In my own experience, it was just different random values that didn't happen to be valid. But now I'm curious -- is there any setting of g++ that would make it fill memory that the standard would otherwise say should be uninitialized?

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• Compare two variant with boost static_visitor

  - by Zozzzzz

  I started to use the boost library a few days ago so my question is maybe trivial. I want to compare two same type variants with a static_visitor. I tried the following, but it don't want to compile. struct compare:public boost::static_visitor<bool> { bool operator()(int& a, int& b) const { return a<b; } bool operator()(double& a, double& b) const { return a<b; } }; int main() { boost::variant<double, int > v1, v2; v1 = 3.14; v2 = 5.25; compare vis; bool b = boost::apply_visitor(vis, v1,v2); cout<<b; return 0; } Thank you for any help or suggestion!

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• Need advice on C++ coding pattern

  - by Kotti

  Hi! I have a working prototype of a game engine and right now I'm doing some refactoring. What I'm asking for is your opinion on usage of the following C++ coding patterns. I have implemented some trivial algorithms for collision detection and they are implemented the following way: Not shown here - class constructor is made private and using algorithms looks like Algorithm::HandleInnerCollision(...) struct Algorithm { // Private routines static bool is_inside(Point& p, Object& object) { // (...) } public: /** * Handle collision where the moving object should be always * located inside the static object * * @param MovingObject & mobject * @param const StaticObject & sobject * @return void * @see */ static void HandleInnerCollision(MovingObject& mobject, const StaticObject& sobject) { // (...) } So, my question is - somebody advised me to do it "the C++" way - so that all functions are wrapped in a namespace, but not in a class. Is there some good way to preserve privating if I will wrap them into a namespace as adviced? What I want to have is a simple interface and ability to call functions as Algorithm::HandleInnerCollision(...) while not polluting the namespace with other functions such as is_inside(...) Of, if you can advise any alternative design pattern for such kind of logics, I would really appreciate that...

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• C++ Virtual Methods for Class-Specific Attributes or External Structure

  - by acanaday

  I have a set of classes which are all derived from a common base class. I want to use these classes polymorphically. The interface defines a set of getter methods whose return values are constant across a given derived class, but vary from one derived class to another. e.g.: enum AVal { A_VAL_ONE, A_VAL_TWO, A_VAL_THREE }; enum BVal { B_VAL_ONE, B_VAL_TWO, B_VAL_THREE }; class Base { //... virtual AVal getAVal() const = 0; virtual BVal getBVal() const = 0; //... }; class One : public Base { //... AVal getAVal() const { return A_VAL_ONE }; BVal getBVal() const { return B_VAL_ONE }; //... }; class Two : public Base { //... AVal getAVal() const { return A_VAL_TWO }; BVal getBVal() const { return B_VAL_TWO }; //... }; etc. Is this a common way of doing things? If performance is an important consideration, would I be better off pulling the attributes out into an external structure, e.g.: struct Vals { AVal a_val; VBal b_val; }; storing a Vals* in each instance, and rewriting Base as follows? class Base { //... public: AVal getAVal() const { return _vals->a_val; }; BVal getBVal() const { return _vals->b_val; }; //... private: Vals* _vals; }; Is the extra dereference essentially the same as the vtable lookup? What is the established idiom for this type of situation? Are both of these solutions dumb? Any insights are greatly appreciated

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• Event Dispatching, void pointer and alternatives

  - by PeeS

  i have my event dispatching / handling functionality working fine, but there is one issue that i need to resolve. Long story short, here are the details. // The event structure struct tEventMessage { // Type of the event int Type; // (void*) Allows those to be casted into per-Type objects void *pArgument1; void *pArgument2; }; I am sending events from different modules in my engine by using the above structure, which requires a pointer to an argument. All messages are queued, and then dispatched on the next ::Tick(). It works fine, untill i try to send something that doesn't exist in next ::Tick, for example: When a mouse click is being handled, it calculates the click coordinates in world space. This is being sent with a pointer to a vector representing that position, but after my program quits that method, this pointer gets invalid obviously, cause local CVector3 is destructed: CVector2 vScreenSpacePosition = vAt; CVector3 v3DPositionA = CVector3(0,0,0); CVector3 v3DPositionB = CVector3(0,0,0); // Screen space to World space calculation for depth zNear v3DPositionA = CMath::UnProject(vScreenSpacePosition, m_vScreenSize, m_Level.GetCurrentCamera()->getViewMatrix(), m_Level.GetCurrentCamera()->getProjectionMatrix(), -1.0 ); // Screen space to World space calculation for depth zFar v3DPositionB = CMath::UnProject(vScreenSpacePosition, m_vScreenSize, m_Level.GetCurrentCamera()->getViewMatrix(), m_Level.GetCurrentCamera()->getProjectionMatrix(), 1.0); // Send zFar position and ScreenSpace position to the handlers // Obviously both vectors won't be valid after this method quits.. CEventDispatcher::Get()->SendEvent(CIEventHandler::EVENT_SYSTEM_FINGER_DOWN, static_cast<void*>(&v3DPositionB), static_cast<void*>(&vScreenSpacePosition)); What i want to ask is, if there is any chance i could make my tEventMessage more 'template', so i can handle sending objects like in the above situation + use what is already implemented? Can't figure it out at the moment.. What else can be done here to allow me to pass some locally available data ? Please can somebody shed a bit of light on this please?

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• Measuring the CPU frequency scaling effect

  - by Bryan Fok

  Recently I am trying to measure the effect of the cpu scaling. Is it accurate if I use this clock to measure it? template<std::intmax_t clock_freq> struct rdtsc_clock { typedef unsigned long long rep; typedef std::ratio<1, clock_freq> period; typedef std::chrono::duration<rep, period> duration; typedef std::chrono::time_point<rdtsc_clock> time_point; static const bool is_steady = true; static time_point now() noexcept { unsigned lo, hi; asm volatile("rdtsc" : "=a" (lo), "=d" (hi)); return time_point(duration(static_cast<rep>(hi) << 32 | lo)); } }; Update: According to the comment from my another post, I believe redtsc cannot use for measure the effect of cpu frequency scaling because the counter from the redtsc does not affected by the CPU frequency, am i right?

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• How to access variables in shared memory

  - by user1723361

  I am trying to create a shared memory segment containing three integers and an array. The segment is created and a pointer is attached, but when I try to access the values of the variables (whether changing, printing, etc.) I get a segmentation fault. Here is the code I tried: #include <stdio.h> #include <stdbool.h> #include <stdlib.h> #include <errno.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/sem.h> #define SIZE 10 int* shm_front; int* shm_end; int* shm_count; int* shm_array; int shm_size = 3*sizeof(int) + sizeof(shm_array[SIZE]); int main(int argc, char* argsv[]) { int shmid; //create shared memory segment if((shmid = shmget(IPC_PRIVATE, shm_size, 0644)) == -1) { printf("error in shmget"); exit(1); } //obtain the pointer to the segment if((shm_front = (int*)shmat(shmid, (void *)0, 0)) == (void *)-1) { printf("error in shmat"); exit(1); } //move down the segment to set the other pointers shm_end = shm_front + 1; shm_count = shm_front + 2; shm_array = shm_front + 3; //tests on shm //*shm_end = 10; //gives segmentation fault //printf("\n%d", *shm_front); //gives segmentation fault //clean-up //get rid of shared memory shmdt(shm_front); shmctl(shmid, IPC_RMID, NULL); //printf("\n\n"); return 0; } I tried accessing the shared memory by dereferencing the pointer to the struct, but got a segmentation fault each time.

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• pthread_create followed by pthread_detach still results in possibly lost error in Valgrind.

  - by alesplin

  I'm having a problem with Valgrind telling me I have some memory possible lost: ==23205== 544 bytes in 2 blocks are possibly lost in loss record 156 of 265 ==23205== at 0x6022879: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==23205== by 0x540E209: allocate_dtv (in /lib/ld-2.12.1.so) ==23205== by 0x540E91D: _dl_allocate_tls (in /lib/ld-2.12.1.so) ==23205== by 0x623068D: pthread_create@@GLIBC_2.2.5 (in /lib/libpthread-2.12.1.so) ==23205== by 0x758D66: MTPCreateThreadPool (MTP.c:290) ==23205== by 0x405787: main (MServer.c:317) The code that creates these threads (MTPCreateThreadPool) basically gets an index into a block of waiting pthread_t slots, and creates a thread with that. TI becomes a pointer to a struct that has a thread index and a pthread_t. (simplified/sanitized): for (tindex = 0; tindex < NumThreads; tindex++) { int rc; TI = &TP->ThreadInfo[tindex]; TI->ThreadID = tindex; rc = pthread_create(&TI->ThreadHandle,NULL,MTPHandleRequestsLoop,TI); /* check for non-success that I've omitted */ pthread_detach(&TI->ThreadHandle); } Then we have a function MTPDestroyThreadPool that loops through all the threads we created and cancels them (since the MTPHandleRequestsLoop doesn't exit). for (tindex = 0; tindex < NumThreads; tindex++) { pthread_cancel(TP->ThreadInfo[tindex].ThreadHandle); } I've read elsewhere (including other questions here on SO) that detaching a thread explicitly would prevent this possibly lost error, but it clearly isn't. Any thoughts?

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• C++ OOP - Can you 'overload a cast' <- hard to explain in 1 sentence

  - by Brandon Miller

  Well, the WinAPI has a POINT struct, but I am trying to make an alternative class to this so you can set the values of x and y from a constructor. /** * X-Y coordinates */ class Point { public: int X, Y; Point(void) : X(0), Y(0) {} Point(int x, int y) : X(x), Y(y) {} Point(const POINT& pt) : X(pt.x), Y(pt.y) {} Point& operator= (const POINT& other) { X = other.x; Y = other.y; } }; // I have an assignment operator and copy constructor. Point myPtA(3,7); Point myPtB(8,5); POINT pt; pt.x = 9; pt.y = 2; // I can assign a 'POINT' to a 'Point' myPtA = pt; // But I also want to be able to assign a 'Point' to a 'POINT' pt = myPtB; Is it possible to overload operator= in a way so that I can assign a Point to a POINT? Or maybe some other method to achieve this? Thanks in advance.

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