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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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Declaring an enum within a class

- by bporter

In the following code snippet, the Color enum is declared within the Car class in order to limit the scope of the enum and to try not to "pollute" the global namespace. class Car { public: enum Color { RED, BLUE, WHITE }; void SetColor( Car::Color color ) { _color = color; } Car::Color GetColor() const { return _color; } private: Car::Color _color; }; (1) Is this a good way to limit the scope of the Color enum? Or, should I declare it outside of the Car class, but possibly within its own namespace or struct? I just came across this article today, which advocates the latter and discusses some nice points about enums: http://gamesfromwithin.com/stupid-c-tricks-2-better-enums. (2) In this example, when working within the class, is it best to code the enum as Car::Color, or would just Color suffice? (I assume the former is better, just in case there is another Color enum declared in the global namespace. That way, at least, we are explicit about the enum to we are referring.) Thanks in advance for any input on this.

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Updating Pointer using signals and slots

- by Umesha MS

Hi, I am very new to the QT; please help me to solve the problem. I am using thread to perform intensive operation in back ground. Meanwhile I want to update the UI, so I am using SIGNALS and SLOTS. To update UI I emit a signal and update UI. Let us consider bellow sample code, struct sample { QString name; QString address; }; void Update(sample *); void sampleFunction() { sample a; a.name = "Sachin Tendulkar"; a.address = "India" emit Update(&a); } In the above code we are creating a local object and passing the address of local object. In the QT document, it says that when we emit a signal it will be placed in the queue and late it will be delivered to the windows. Since my object is in local scope it will be delete once it goes out of the scope. Please tell me a way to send a pointer in a signal.

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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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Access array of c-structs using Python ctypes

- by sadris

I have a C-function that allocates memory at the address passed to and is accessed via Python. The pointer contents does contain an array of structs in the C code, but I am unable to get ctypes to access the array properly beyond the 0th element. How can I get the proper memory offset to be able to access the non-zero elements? Python's ctypes.memset is complaining about TypeErrors if I try to use their ctypes.memset function. typedef struct td_Group { unsigned int group_id; char groupname[256]; char date_created[32]; char date_modified[32]; unsigned int user_modified; unsigned int user_created; } Group; int getGroups(LIBmanager * handler, Group ** unallocatedPointer); ############# python code below: class Group(Structure): _fields_ = [("group_id", c_uint), ("groupname", c_char*256), ("date_created", c_char*32), ("date_modified", c_char*32), ("user_modified", c_uint), ("user_created", c_uint)] myGroups = c_void_p() count = libnativetest.getGroups( nativePointer, byref(myGroups) ) casted = cast( myGroups, POINTER(Group*count) ) for x in range(0,count): theGroup = cast( casted[x], POINTER(Group) ) # this only works for the first entry in the array: print "~~~~~~~~~~" + theGroup.contents.groupname Related: Access c_char_p_Array_256 in Python using ctypes

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Crash in C++ Code

- by Ankuj

I am trying to list all files in a directory recursively. But my code crashes without giving any error. When the given file is directory I recursively call the function or else print its name. I am using dirent.h int list_file(string path) { DIR *dir; struct dirent *ent; char *c_style_path; c_style_path = new char[path.length()]; c_style_path = (char *)path.c_str(); dir = opendir (c_style_path); if (dir != NULL) { /* print all the files and directories within directory */ while ((ent = readdir (dir)) != NULL) { if(ent->d_type == DT_DIR && (strcmp(ent->d_name,".")!=0) && (strcmp(ent->d_name,"..")!=0)) { string tmp = path + "\\" + ent->d_name; list_file(tmp); } else { cout<<ent->d_name<<endl; } } closedir (dir); } else { /* could not open directory */ perror (""); return EXIT_FAILURE; } delete [] c_style_path; return 0; } I am not getting as to what I am doing wrong here. Any clues ?

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why cannot use uncaught_exception in dtor?

- by camino

Hi , Herb Sutter in his article http://www.gotw.ca/gotw/047.htm pointed out that we cannot use uncaught_exception in desturctor function, // Why the wrong solution is wrong // U::~U() { try { T t; // do work } catch( ... ) { // clean up } } If a U object is destroyed due to stack unwinding during to exception propagation, T::~T will fail to use the "code that could throw" path even though it safely could. but I write a test program, and T::~T in fact didn't use the "code that could throw" #include <exception> #include <iostream> using namespace std; class T { public: ~T() { if( !std::uncaught_exception() ) { cout<<"can throw"<<endl; throw 1; } else { cout<<"cannot throw"<<endl; } } }; struct U { ~U() { try { T t; } catch( ... ) { } } }; void f() { U u; throw 2; } int main() { try { f(); } catch(...) {} } output is : cannot throw did I miss something? Thanks

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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++ Declaring an enum within a class

- by bporter

In the following code snippet, the Color enum is declared within the Car class in order to limit the scope of the enum and to try not to "pollute" the global namespace. class Car { public: enum Color { RED, BLUE, WHITE }; void SetColor( Car::Color color ) { _color = color; } Car::Color GetColor() const { return _color; } private: Car::Color _color; }; (1) Is this a good way to limit the scope of the Color enum? Or, should I declare it outside of the Car class, but possibly within its own namespace or struct? I just came across this article today, which advocates the latter and discusses some nice points about enums: http://gamesfromwithin.com/stupid-c-tricks-2-better-enums. (2) In this example, when working within the class, is it best to code the enum as Car::Color, or would just Color suffice? (I assume the former is better, just in case there is another Color enum declared in the global namespace. That way, at least, we are explicit about the enum to we are referring.) Thanks in advance for any input on this.

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Convert a binary tree to linked list, breadth first, constant storage/destructive

- by Merlyn Morgan-Graham

This is not homework, and I don't need to answer it, but now I have become obsessed :) The problem is: Design an algorithm to destructively flatten a binary tree to a linked list, breadth-first. Okay, easy enough. Just build a queue, and do what you have to. That was the warm-up. Now, implement it with constant storage (recursion, if you can figure out an answer using it, is logarithmic storage, not constant). I found a solution to this problem on the Internet about a year back, but now I've forgotten it, and I want to know :) The trick, as far as I remember, involved using the tree to implement the queue, taking advantage of the destructive nature of the algorithm. When you are linking the list, you are also pushing an item into the queue. Each time I try to solve this, I lose nodes (such as each time I link the next node/add to the queue), I require extra storage, or I can't figure out the convoluted method I need to get back to a node that has the pointer I need. Even the link to that original article/post would be useful to me :) Google is giving me no joy. Edit: Jérémie pointed out that there is a fairly simple (and well known answer) if you have a parent pointer. While I now think he is correct about the original solution containing a parent pointer, I really wanted to solve the problem without it :) The refined requirements use this definition for the node: struct tree_node { int value; tree_node* left; tree_node* right; };

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Why my linux signal handler run only once

- by Henry Fané

#include <iostream> #include <signal.h> #include <fenv.h> #include <string.h> void signal_handler(int sig, siginfo_t *siginfo, void* context) { std::cout << " signal_handler " << fetestexcept(FE_ALL_EXCEPT) << std::endl; throw "exception"; } void divide() { float a = 1000., b = 0., c, f = 1e-300; c = a / b; std::cout << c << " and f = " << f << std::endl; } void init_sig_hanlder() { feenableexcept(FE_ALL_EXCEPT); struct sigaction sa, initial_sa; sa.sa_sigaction = &signal_handler ; sigemptyset( &sa.sa_mask ) ; sa.sa_flags = SA_SIGINFO; // man sigaction(3) // allows for void(*)(int,siginfo_t*,void*) handler sigaction(SIGFPE, &sa, &initial_sa); } int main(int argc, char** argv) { init_sig_hanlder(); while(true) { try { sleep(1); divide(); } catch(const char * a) { std::cout << "Exception in catch: " << a << std::endl; } catch(...) { std::cout << "Exception in ..." << std::endl; } } return 0; } Produce the following results on Linux/g++4.2: signal_handler 0 Exception in catch: exception inf and f = 0 inf and f = 0 inf and f = 0 inf and f = 0 So, signal handler is executed the first time but the next fp exception does not trigger the handler again. Where am I wrong ?

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Why is joining two vectors simply not working?

- by Jim

I have two vectors of MyObj structs. MyObj is defined as follows: struct MyObj { float x, y; unsigned int data[8]; unsigned int tmp[1]; MyObj(const MyObj &m) { x = m.x; y = m.y; tmp[0] = 0; for (int i = 0; i < 8; ++i) { data[i] = m.data[i]; } } }; I then have two vectors... vector<MyObj> v1; vector<MyObj> v2; // both get data eventually. v1.insert(v1.end(), v2.begin(), v2.end()); v2 has 3535004 elements in my experiment. v1 is similarly sized. I've also tried building a new vector and just using .push_back to build it from both vectors. Essentially, when I try to merge the two vectors I just get an error from visual studio saying "Debug error! R6010, abort() has been called". Very non-useful... So my question is: what could be causing this error, and how can I solve it? Thank you

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Please help me optimize my Python code

- by Haidon

Beginner here! Forgive me in advance for raising what is probably an incredibly simple problem. I've been trying to put together a Python script that runs multiple find-and-replace actions and a few similar things on a specified plain-text file. It works, but from a programming perspective I doubt it works well. How would I best go about optimizing the actions made upon the 'outtext' variable? At the moment it's basically doing a very similar thing four times over... import binascii import re import struct import sys infile = sys.argv[1] charenc = sys.argv[2] outFile=infile+'.tex' findreplace = [ ('TERM1', 'TERM2'), ('TERM3', 'TERM4'), ('TERM5', 'TERM6'), ] inF = open(infile,'rb') s=unicode(inF.read(),charenc) inF.close() # THIS IS VERY MESSY. for couple in findreplace: outtext=s.replace(couple[0],couple[1]) s=outtext for couple in findreplace: outtext=re.compile('Title: (.*)', re.I).sub(r'\\title'+ r'{\1}', s) s=outtext for couple in findreplace: outtext=re.compile('Author: (.*)', re.I).sub(r'\\author'+ r'{\1}', s) s=outtext for couple in findreplace: outtext=re.compile('Date: (.*)', re.I).sub(r'\\date'+ r'{\1}', s) s=outtext # END MESSY SECTION. outF = open(outFile,'wb') outF.write(outtext.encode('utf-8')) outF.close()

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C++ template and pointers

- by Kary

I have a problem with a template and pointers ( I think ). Below is the part of my code: /* ItemCollection.h */ #ifndef ITEMCOLLECTION_H #define ITEMCOLLECTION_H #include <cstddef> using namespace std; template <class T> class ItemCollection { public: // constructor //destructor void insertItem( const T ); private: struct Item { T price; Item* left; Item* right; }; Item* root; Item* insert( T, Item* ); }; #endif And the file with function defintion: /* ItemCollectionTemp.h-member functions defintion */ #include <iostream> #include <cstddef> #include "ItemCollection.h" template <class Type> Item* ItemCollection <T>::insert( T p, Item* ptr) { // function body } Here are the errors which are generated by this line of code: Item* ItemCollection <T>::insert( T p, Item* ptr) Errors: error C2143: syntax error : missing ';' before '*' error C4430: missing type specifier - int assumed. Note: C++ does not support default-int error C2065: 'Type' : undeclared identifier error C2065: 'Type' : undeclared identifier error C2146: syntax error : missing ')' before identifier 'p' error C4430: missing type specifier - int assumed. Note: C++ does not support default-int error C2470: 'ItemCollection::insert' : looks like a function definition, but there is no parameter list; skipping apparent body error C2072: 'ItemCollection::insert': initialization of a function error C2059: syntax error : ')' Any help is much appreciated.

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cuda 5.0 namespaces for contant memory variable usage

- by Psypher

In my program I want to use a structure containing constant variables and keep it on device all long as the program executes to completion. I have several header files containing the declaration of 'global' functions and their respective '.cu' files for their definitions. I kept this scheme because it helps me contain similar code in one place. e.g. all the 'device' functions required to complete 'KERNEL_1' are separated from those 'device' functions required to complete 'KERNEL_2' along with kernels definitions. I had no problems with this scheme during compilation and linking. Until I encountered constant variables. I want to use the same constant variable through all kernels and device functions but it doesn't seem to work. ########################################################################## CODE EXAMPLE ########################################################################### filename: 'common.h' -------------------------------------------------------------------------- typedef struct { double height; double weight; int age; } __CONSTANTS; __constant__ __CONSTANTS d_const; --------------------------------------------------------------------------- filename: main.cu --------------------------------------------------------------------------- #include "common.h" #include "gpukernels.h" int main(int argc, char **argv) { __CONSTANTS T; T.height = 1.79; T.weight = 73.2; T.age = 26; cudaMemcpyToSymbol(d_consts, &T, sizeof(__CONSTANTS)); test_kernel <<< 1, 16 >>>(); cudaDeviceSynchronize(); } --------------------------------------------------------------------------- filename: gpukernels.h --------------------------------------------------------------------------- __global__ void test_kernel(); --------------------------------------------------------------------------- filename: gpukernels.cu --------------------------------------------------------------------------- #include <stdio.h> #include "gpukernels.h" #include "common.h" __global__ void test_kernel() { printf("Id: %d, height: %f, weight: %f\n", threadIdx.x, d_const.height, d_const.weight); } When I execute this code, the kernel executes, displays the thread ids, but the constant values are displayed as zeros. How can I fix this?

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Class lookup structure array in C++

- by wyatt

I'm trying to create a structure array which links input strings to classes as follows: struct {string command; CommandPath cPath;} cPathLookup[] = { {"set an alarm", AlarmCommandPath}, {"send an email", EmailCommandPath}, {"", NULL} }; which will be used as follows: CommandPath *cPath = NULL; string input; getline(cin, input); for(int i = 0; cPathLookup[i] != ""; i++) { if(cPathLookup[i].command == input) cPath = new cPathLookup[i].cPath; } Obviously, this code is meaningless, but I think my intention is apparent - depending on input, I'd like cPath to be initialized as either a new AlarmCommandPath or a new EmailCommandPath. I could handle it with a function returning an instance depending on input, but a whole sequence of ifs just seems inelegant. I should also note that, in case it's not apparent and important, that AlarmCommandPath and EmailCommandPath are derived from CommandPath, and CommandPath is an abstract class. Thanks for any help you can offer. EDIT: I just noticed that, in spite of CommandPath being abstract, I have a declaration: CommandPath *cPath = NULL; in working code. Why does that compile?

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VB .NET Passing a Structure containing an array of String and an array of Integer into a C++ DLL

- by DanJunior

Hi everyone, I'm having problems with marshalling in VB .NET to C++, here's the code : In the C++ DLL : struct APP_PARAM { int numData; LPCSTR *text; int *values; }; int App::StartApp(APP_PARAM params) { for (int i = 0; i < numLines; i++) { OutputDebugString(params.text[i]); } } In VB .NET : <StructLayoutAttribute(LayoutKind.Sequential)> _ Public Structure APP_PARAM Public numData As Integer Public text As System.IntPtr Public values As System.IntPtr End Structure Declare Function StartApp Lib "AppSupport.dll" (ByVal params As APP_PARAM) As Integer Sub Main() Dim params As APP_PARAM params.numData = 3 Dim text As String() = {"A", "B", "C"} Dim textHandle As GCHandle = GCHandle.Alloc(text) params.text = GCHandle.ToIntPtr(textHandle) Dim values As Integer() = {10, 20, 30} Dim valuesHandle As GCHandle = GCHandle.Alloc(values) params.values = GCHandle.ToIntPtr(heightHandle) StartApp(params) textHandle.Free() valuesHandle.Free() End Sub I checked the C++ side, the output from the OutputDebugString is garbage, the text array contains random characters. What is the correct way to do this?? Thanks a lot...

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C++ new memory allocation fragmentation

- by tamulj

I was trying to look at the behavior of the new allocator and why it doesn't place data contiguously. My code: struct ci { char c; int i; } template <typename T> void memTest() { T * pLast = new T(); for(int i = 0; i < 20; ++i) { T * pNew = new T(); cout << (pNew - pLast) << " "; pLast = pNew; } } So I ran this with char, int, ci. Most allocations were a fixed length from the last, sometimes there were odd jumps from one available block to another. sizeof(char) : 1 Average Jump: 64 bytes sizeof(int): 4 Average Jump: 16 sizeof(ci): 8 (int has to be placed on a 4 byte align) Average Jump: 9 Can anyone explain why the allocator is fragmenting memory like this? Also why is the jump for char so much larger then ints and a structure that contains both an int and char.

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C++ privately contructed class

- by Nona Urbiz

How can I call a function and keep my constructor private? If I make the class static, I need to declare an object name which the compiler uses to call the constructor, which it cannot if the constructor is private (also the object would be extraneous). Here is the code I am attempting to use (it is not compilable): I want to keep the constructor private because I will later be doing a lot of checks before adding an object, modifying previous objects when all submitted variables are not unique rather than creating new objects. #include <iostream> #include <fstream> #include <regex> #include <string> #include <list> #include <map> using namespace std; using namespace tr1; class Referral { public: string url; map<string, int> keywords; static bool submit(string url, string keyword, int occurrences) { //if(Referrals.all.size == 0){ // Referral(url, keyword, occurrences); //} } private: list<string> urls; Referral(string url, string keyword, int occurrences) { url = url; keywords[keyword] = occurrences; Referrals.all.push_back(this); } }; struct All { list<Referral> all; }Referrals; int main() { Referral.submit("url", "keyword", 1); }

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Parsing string based on initial format

- by Kayla

I'm trying to parse a set of lines and extract certain parts of the string based on an initial format (reading a configuration file). A little more explanation: the format can contain up to 4 parts to be formatted. This case, %S will skip the part, %a-%c will extract the part and will be treated as a string, %d as int. What I am trying to do now is to come up with some clever way to parse it. So far I came up with the following prototype. However, my pointer arithmetic still needs some work to skip/extract the parts. Ultimately each part will be stored on an array of structs. Such as: struct st_temp { char *parta; char *partb; char *partc; char *partd; }; ... #include <stdio.h> #include <string.h> #define DIM(x) (sizeof(x)/sizeof(*(x))) void process (const char *fmt, const char *line) { char c; const char *src = fmt; while ((c = *src++) != '\0') { if (c == 'S'); // skip part else if (c == 'a'); // extract %a else if (c == 'b'); // extract %b else if (c == 'c'); // extract %c else if (c == 'd'); // extract %d (int) else { printf("Unknown format\n"); exit(1); } } } static const char *input[] = { "bar 200.1 / / (zaz) - \"bon 10\"", "foo 100.1 / / (baz) - \"apt 20\"", }; int main (void) { const char *fmt = "%S %a / / (%b) - \"%c %d\""; size_t i; for(i = 0; i < DIM (input); i++) { process (fmt, input[i]); } return (0); }

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Changing file permissions in kernel.

- by Mehrdad

I am writing kernel module(C in Linux) and I want to change the permission of the other files in it. any solution? since I am in kernel I can't use chmod syscall and ... thanks for your help This is my Makefile: > obj-m += ca.o > > all: > make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules > > clean: > make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean And this is my Code: > #include <linux/string.h> > #include <linux/mm.h> > /* Snip, tons of includes (all of them :))*/ > #include <linux/delay.h> .... int procfile_write(struct file *file, > const char *buffer, unsigned long > count, > void *data) { ... sys_chmod(path, per); ... } ... When Making it gives a warning: WARNING: "sys_chmod" [file] undefiened and when loading the module with "sudo insmod" it gives this error: Unknown sybol in module it seems that this error happens especialy in kernel modules. any idea? again thanks!

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How to easily apply a function to a collection in C++

- by Jesse Beder

I'm storing images as arrays, templated based on the type of their elements, like Image<unsigned> or Image<float>, etc. Frequently, I need to perform operations on these images; for example, I might need to add two images, or square an image (elementwise), and so on. All of the operations are elementwise. I'd like get as close as possible to writing things like: float Add(float a, float b) { return a+b; } Image<float> result = Add(img1, img2); and even better, things like complex ComplexCombine(float a, float b) { return complex(a, b); } Image<complex> result = ComplexCombine(img1, img2); or struct FindMax { unsigned currentMax; FindMax(): currentMax(0) {} void operator(unsigned a) { if(a > currentMax) currentMax = a; } }; FindMax findMax; findMax(img); findMax.currentMax; // now contains the maximum value of 'img' Now, I obviously can't exactly do that; I've written something so that I can call: Image<float> result = Apply(img1, img2, Add); but I can't seem to figure out a generic way for it to detect the return type of the function/function object passed, so my ComplexCombine example above is out; also, I have to write a new one for each number of arguments I'd like to pass (which seems inevitable). Any thoughts on how to achieve this (with as little boilerplate code as possible)?

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What does the Asterisk * mean in Objective-C?

- by Thanks

Is it true, that the Asterisk always means "Hey, that is a pointer!" And an Pointer always holds an memory adress? (Yes I know for the exception that a * is used for math operation) For Example: NSString* myString; or SomeClass* thatClass; or (*somePointerToAStruct).myStructComponent = 5; I feel that there is more I need to know about the Asterirsk (*) than that I use it when defining an Variable that is a pointer to a class. Because sometimes I already say in the declaration of an parameter that the Parameter variable is a pointer, and still I have to use the Asterisk in front of the Variable in order to access the value. That recently happened after I wanted to pass a pointer of an struct to a method in a way like [myObj myMethod:&myStruct], I could not access a component value from that structure even though my method declaration already said that there is a parameter (DemoStruct*)myVar which indeed should be already known as a pointer to that demostruct, still I had always to say: "Man, compiler. Listen! It IIISSS a pointer:" and write: (*myVar).myStructComponentX = 5; I really really really do not understand why I have to say that twice. And only in this case. When I use the Asterisk in context of an NSString* myString then I can just access myString however I like, without telling the compiler each time that it's a pointer. i.e. like using *myString = @"yep". It just makes no sense to me.

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Vector Usage in MPI(C++)

- by lsk1985

I am new to MPI programming,stiil learning , i was successful till creating the Derived data-types by defining the structures . Now i want to include Vector in my structure and want to send the data across the Process. for ex: struct Structure{ //Constructor Structure(): X(nodes),mass(nodes),ac(nodes) { //code to calculate the mass and accelerations } //Destructor Structure() {} //Variables double radius; double volume; vector<double> mass; vector<double> area; //and some other variables //Methods to calculate some physical properties Now using MPI i want to sent the data in the structure across the processes. Is it possible for me to create the MPI_type_struct vectors included and send the data? I tried reading through forums, but i am not able to get the clear picture from the responses given there. Hope i would be able to get a clear idea or approach to send the data PS: i can send the data individually , but its an overhead of sending the data using may MPI_Send/Recieve if we consider the domain very large(say 10000*10000)

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Pointers into elements in a container

- by Pillsy

Say I have an object: struct Foo { int bar_; Foo(int bar) bar_(bar) {} }; and I have an STL container that contains Foos, perhaps a vector, and I take // Elsewhere... vector<Foo> vec; vec.push_back(Foo(4)); int *p = &(vec[0].bar_) This is a terrible idea, right? The reason is that vector is going to be storing its elements in a dynamically allocated array somewhere, and eventually, if you add enough elements, it will have to allocate another array, copy over all the elements of the original array, and delete the old array. After that happens, p points to garbage. This is why many operations on a vector will invalidate iterators. It seems like it would be reasonable to assume that an operation that would invalidate iterators from a container will also invalidate pointers to data members of container elements, and that if an operation doesn't invalidate iterators, those pointers will still be safe. However, many reasonable assumptions are false. Is this one of them?

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