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  • Implementing a list with unique_ptr<>? [migrated]

    - by Alexander Duchene
    As I understand it, a unique_ptr signifies exclusive ownership. A singly linked list seems to fit this, with each node owning the next, like (pseduocode alert) class node{ public: unique_ptr<node> next; int value; }; but I don't understand how to perform operations like traversing the list, where I'm used to doing here=here->next; How do you implement data structures using unique_ptr's? Are they the right tool for the job?

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  • How to copy an array of char pointers with a larger list of char pointers?

    - by Casey Link
    My function is being passed a struct containing, among other things, a NULL terminated array of pointers to words making up a command with arguments. I'm performing a glob match on the list of arguments, to expand them into a full list of files, then I want to replace the passed argument array with the new expanded one. The globbing is working fine, that is, g.gl_pathv is populated with the list of expected files. However, I am having trouble copying this array into the struct I was given. #include <glob.h> struct command { char **argv; // other fields... } void myFunction( struct command * cmd ) { char **p = cmd->argv; char* program = *p++; // save the program name (e.g 'ls', and increment to the first argument glob_t g; memset(&g, 0, sizeof(g)); int res = glob(*p, 0, NULL, &g); *p++ // increment while (*p) { glob(*p++, GLOB_APPEND, NULL, &g); // append the matches } // here i want to replace cmd->argv with the expanded g.gl_pathv memcpy(cmd->argv, g.gl_pathv, g.gl_pathc ); // this doesn't work globfree(&g); }

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  • Sync Framework Considerations for Smart Client app

    - by DarkwingDuck
    Microsoft Sync Framework with SQL 2005? Is it possible? It seems to hint that the OOTB providers use SQL2008 functionality. I'm looking for some quick wins in relation to a sync project. The client app will be offline for a number of days. There will be a central server that MUST be SQL Server 2005. I can use .net 3.5. Basically the client app could go offline for a week. When it comes back online it needs to sync its data. But the good thing is that the data only needs to push to the server. The stuff that syncs back to the client will just be lookup data which the client never changes. So this means I don't care about sync collisions. To simplify the scenario for you, this smart client goes offline and the user surveys data about some observations. They enter the data into the system. When the laptop is reconnected to the network, it syncs back all that data to the server. There will be other clients doing the same thing too, but no one ever touches each other's data. Then there are some reports on the server for viewing the data that has been pushed to the server. This also needs to use ClickOnce. My biggest concern is that there is an interim release while a client is offline. This release might require a new field in the database, and a new field to fill in on the survey. Obviously that new field will be nullable because we can't update old data, that's fine to set as an assumption. But when the client connects up and its local data schema and the server schema don't match, will sync framework be able to handle this? After the data is pushed to the server it is discarded locally. Hope my problem makes sense.

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  • PHP 'smart' search engine to search Mysql tables advice

    - by Anonymous12345
    I am creating a search engine for my php based website. I need to search a mysql table. Thing is, the search engine must be pretty 'smart', so that users can easily find their items (it's a classifieds website). I have currently set up a FULLTEXT search with this piece of code: MATCH (headline) AGAINST ($querystring) But this isn't enough... For instance, lets say the field headline contains something like Bmw 330ci. If I search for 330, I wont get any results. The ending ('ci') is just one of many endings in car models which must be taken into account when searching the table. Or what if the headline field is bmw330? Also no results, because it only matches full words. Or also, what if the headline is bmw 330, and I search for bmw 520, still with FULLTEXT I will get the bmw 330 as a result, even though I searched for bmw 520... Not good! How should I solve this problem?

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  • Problem with passing vector of pointers to objects to member function of another object

    - by Jamesz
    Hi, I have a vector of pointers to Mouse objects called 'mice'. I'm passing the mice to the cat by reference. vector <Mouse*> mice; Cat * c; c->lookForMouse(&mice); And here's my lookForMouse() member function void Cat::lookForMouse(vector <Mouse*> *mice) { ... } And now to the problem! Within the function above, I can't seem to access my mice. This below will not work mice[i]->isActive(); The error message I receive suggests to use mice[i].isActive(), but this throws an error saying isActive() is not a member of std::vector<_Ty ... This works though... vector <Mouse*> miceCopy = *mice; miceCopy[i]->isActive(); I understand that I shouldn't be creating another vector of mice here, it defeats the whole point of passing it by reference (let me know if I'm wrong)... Why can't I do mice[i]-isActive() What should I be doing? Thanks for your time and help :D James.

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  • C++ design question, container of instances and pointers

    - by Tom
    Hi all, Im wondering something. I have class Polygon, which composes a vector of Line (another class here) class Polygon { std::vector<Line> lines; public: const_iterator begin() const; const_iterator end() const; } On the other hand, I have a function, that calculates a vector of pointers to lines, and based on those lines, should return a pointer to a Polygon. Polygon* foo(Polygon& p){ std::vector<Line> lines = bar (p.begin(),p.end()); return new Polygon(lines); } Here's the question: I can always add a Polygon (vector Is there a better way that dereferencing each element of the vector and assigning it to the existing vector container? //for line in vector<Line*> v //vcopy is an instance of vector<Line> vcopy.push_back(*(v.at(i)) I think not, but I dont really like that approach. Hopefully, I will be able to convince the author of the class to change it, but I cant base my coding right now to that fact (and i'm scared of a performance hit). Thanks in advance.

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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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  • smart phone UI limitations

    - by Manny
    I would like to know, what limitations there are for how far one can go in terms of replacing UI components of current touch screen smart phones, in particular iPhone, Blackberry and android based phones. What I would like to do is create a custom UI for dialing out and incoming calls. I have some experience with Blackberry development. The theme builder for it, can be used to customize certain items on the incoming call screen, but it doesn't look like that you can increase the size of answer button. I know Blackberry also gives you access to all the phone APIs, but I'm not sure that you can create your own UI that can gain preference over the Blackberry incoming call screen. And if you try to customize the incoming call screen by adding any buttons to it, they would be rendered as pictures. I could possibly design a complete UI for android, since different manufactures have different UI for android based phones. Can I do what I want to do using iPhone, Blackberry or android? Or any other phone for that matter? I am guessing may be for Nokia phones using Qt, but I prefer the 3 platforms I listed. Thanks for all your help.

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  • push(ing)_back objects pointers within a loop

    - by Jose Manuel Albornoz
    Consider the following: I have a class CDevices containing, amongst others, a string member class CDevice { public: CDevice(void); ~CDevice(void); // device name std::string Device_Name; etc... } and somewhere else in my code I define another class that contains a vector of pointers to CDevices class CDevice; class CServers { public: CServers(void); ~CServers(void); // Devices vector vector<CDevice*> Devices; etc... } The problem appears in the following lines in my main.c pDevice = new CDevice; pDevice->Device_Name = "de"; Devices.push_back(pDevice); pDevice->Device_Name = " revolotiunibus"; Devices.push_back(pDevice); pDevice->Device_Name = " orbium"; Devices.push_back(pDevice); pDevice->Device_Name = " coelestium"; Devices.push_back(pDevice); for(int i = 0; i < (int)Devices.size(); ++i) cout << "\nLoad name = " << Devices.at(i)->Device_Name << endl; The output I get is " coelestium" repeated four times: each time I push_back a new element into the vector all of the already existing elements take the value of the one which has just been added. I have also tried using iterators to recover each element in the vector with the same results. Could someone please tell me what's wrong here? Thankx

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  • C++ Function pointers vs Switch

    - by Perfix
    What is faster: Function pointers or switch? The switch statement would have around 30 cases, consisting of enumarated unsigned ints from 0 to 30. I could do the following: class myType { FunctionEnum func; string argv[123]; int someOtherValue; }; // In another file: myType current; // Iterate through a vector containing lots of myTypes // ... for ( i=0; i < myVecSize; i ++ ) switch ( current.func ) { case 1: //... break; // ........ case 30: // blah break; } And go trough the switch with func every time. The good thing about switch would also be that my code is more organized than with 30 functions. Or I could do that (not so sure with that): class myType { myReturnType (*func); string argv[123]; int someOtherValue; }; I'd have 30 different functions then, at the beginning a pointer to one of them is assigned to myType. What is probably faster: Switch statement or function pointer? Calls per second: Around 10 million. I can't just test it out - that would require me to rewrite the whole thing. Currently using switch. I'm building an interpreter which I want to be faster than Python & Ruby - every clock cycle matters!

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  • Problem with passing array of pointers to struct among functions in C

    - by karatemonkey
    The Code that follows segfaults on the call to strncpy and I can't see what I am doing wrong. I need another set of eyes to look it this. Essentially I am trying to alloc memory for a struct that is pointed to by an element in a array of pointers to struct. #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX_POLICY_NAME_SIZE 64 #define POLICY_FILES_TO_BE_PROCESSED "SPFPolicyFilesReceivedOffline\0" typedef struct TarPolicyPair { int AppearanceTime; char *IndividualFile; char *FullPolicyFile; } PolicyPair; enum { bwlist = 0, fzacts, atksig, rules, MaxNumberFileTypes }; void SPFCreateIndividualPolicyListing(PolicyPair *IndividualPolicyPairtoCreate ) { IndividualPolicyPairtoCreate = (PolicyPair *) malloc(sizeof(PolicyPair)); IndividualPolicyPairtoCreate->IndividualFile = (char *)malloc((MAX_POLICY_NAME_SIZE * sizeof(char))); IndividualPolicyPairtoCreate->FullPolicyFile = (char *)malloc((MAX_POLICY_NAME_SIZE * sizeof(char))); IndividualPolicyPairtoCreate->AppearanceTime = 0; memset(IndividualPolicyPairtoCreate->IndividualFile, '\0', (MAX_POLICY_NAME_SIZE * sizeof(char))); memset(IndividualPolicyPairtoCreate->FullPolicyFile, '\0', (MAX_POLICY_NAME_SIZE * sizeof(char))); } void SPFCreateFullPolicyListing(SPFPolicyPair **CurrentPolicyPair, char *PolicyName, char *PolicyRename) { int i; for(i = 0; i < MaxNumberFileTypes; i++) { CreateIndividualPolicyListing((CurrentPolicyPair[i])); // segfaults on this call strncpy((*CurrentPolicyPair)[i].IndividualFile, POLICY_FILES_TO_BE_PROCESSED, (SPF_POLICY_NAME_SIZE * sizeof(char))); } } int main() { SPFPolicyPair *CurrentPolicyPair[MaxNumberFileTypes] = {NULL, NULL, NULL, NULL}; int i; CreateFullPolicyListing(&CurrentPolicyPair, POLICY_FILES_TO_BE_PROCESSED, POLICY_FILES_TO_BE_PROCESSED); return 0; }

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  • deleting an array that stores pointers to some objects

    - by memC
    hi, I am storing pointers to elements of a vec_A in an array A* a_ptrs[3] . Assume that vec_A will not be resized. So, a_ptrs[i] will point to the correct element. My question is: Suppose A* a_ptrs[3] is declared in a class B. Since it is not created using 'new' I am guessing I don't need to delete it in the destructor. Am I right?? class A { public: int getNumber(); A(int val); ~A(){}; private: int num; }; A::A(int val){ num = val; }; int A::getNumber(){ return num; }; int main(){ int i =0; int num; std::vector<A> vec_A; for ( i = 0; i < 10; i++){ vec_A.push_back(A(i)); } A* a_ptrs[3]; a_ptrs[0] = &vec_A[0]; a_ptrs[1] = &vec_A[3]; a_ptrs[2] = &vec_A[5]; for (i = 0; i<3; i++){ std::cout<<"\n: a_ptrs[i].getNumber() = "<<a_ptrs[i]->getNumber(); } std::cout << "\nPress RETURN to continue..."; std::cin.get(); return 0; }

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  • c++ Multiple Inheritance - Compiler modifying my pointers

    - by Bob
    If I run the following code, I get different addresses printed. Why? class Base1 { int x; }; class Base2 { int y; }; class Derived : public Base1, public Base2 { }; union U { Base2* b; Derived* d; U(Base2* b2) : b(b) {} }; int main() { Derived* d = new Derived; cout << d << "\n"; cout << U(d).d << "\n"; return 0; } Even more fun is if you repeatedly go in and out of the union the address keeps incrementing by 4, like this int main() { Derived* d = new Derived; cout << d << "\n"; d = U(d).d; cout << d << "\n"; d = U(d).d; cout << d << "\n"; return 0; } If the union is modified like this, then the problem goes away union U { void* v; Base2* b; Derived* d; U(void* v) : v(v) {} }; Also, if either base class is made empty, the problem goes away. Is this a compiler bug? I want it to leave my pointers the hell alone.

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  • Pointer arithmetic and arrays: what's really legal?

    - by bitcruncher
    Consider the following statements: int *pFarr, *pVarr; int farr[3] = {11,22,33}; int varr[3] = {7,8,9}; pFarr = &(farr[0]); pVarr = varr; At this stage, both pointers are pointing at the start of each respective array address. For *pFarr, we are presently looking at 11 and for *pVarr, 7. Equally, if I request the contents of each array through *farr and *varr, i also get 11 and 7. So far so good. Now, let's try pFarr++ and pVarr++. Great. We're now looking at 22 and 8, as expected. But now... Trying to move up farr++ and varr++ ... and we get "wrong type of argument to increment". Now, I recognize the difference between an array pointer and a regular pointer, but since their behaviour is similar, why this limitation? This is further confusing to me when I also consider that in the same program I can call the following function in an ostensibly correct way and in another incorrect way, and I get the same behaviour, though in contrast to what happened in the code posted above!? working_on_pointers ( pFarr, farr ); // calling with expected parameters working_on_pointers ( farr, pFarr ); // calling with inverted parameters . void working_on_pointers ( int *pExpect, int aExpect[] ) { printf("%i", *pExpect); // displays the contents of pExpect ok printf("%i", *aExpect); // displays the contents of aExpect ok pExpect++; // no warnings or errors aExpect++; // no warnings or errors printf("%i", *pExpect); // displays the next element or an overflow element (with no errors) printf("%i", *aExpect); // displays the next element or an overflow element (with no errors) } Could someone help me to understand why array pointers and pointers behave in similar ways in some contexts, but different in others? So many thanks. EDIT: Noobs like myself could further benefit from this resource: http://www.panix.com/~elflord/cpp/gotchas/index.shtml

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  • How to access pixels of an NSBitmapImageRep?

    - by Paperflyer
    I have an NSBitmapImageRep that is created like this: NSBitmapImageRep *imageRep = [[NSBitmapImageRep alloc] initWithBitmapDataPlanes:NULL pixelsWide:waveformSize.width pixelsHigh:waveformSize.height bitsPerSample:8 samplesPerPixel:4 hasAlpha:YES isPlanar:YES colorSpaceName:NSCalibratedRGBColorSpace bytesPerRow:0 bitsPerPixel:0]; Now I want to access the pixel data so I get a pointer to the pixel planes using unsigned char *bitmapData; [imageRep getBitmapDataPlanes:&bitmapData]; According to the Documentation this returns a C array of five character pointers. But how can it do that? since the type of the argument is unsigned char **, it can only return an array of chars, but not an array of char pointers. So, this leaves me wondering how to access the individual pixels. Do you have an idea how to do that? (I know there is the method – setColor:atX:y:, but it seems to be pretty slow if invoked for every single pixel of a big bitmap.)

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  • Function pointer arrays in Fortran

    - by Eduardo Dobay
    I can create function pointers in Fortran 90, with code like real, external :: f and then use f as an argument to another function/subroutine. But what if I want an array of function pointers? In C I would just do double (*f[])(int); to create an array of functions returning double and taking an integer argument. I tried the most obvious, real, external, dimension(3) :: f but gfortran doesn't let me mix EXTERNAL and DIMENSION. Is there any way to do what I want? (The context for this is a program for solving a system of differential equations, so I could input the equations without having a million parameters in my subroutines.)

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  • Pointer to auto_ptr instead of a classical double pointer

    - by Pin
    Hello. I'm quite new to smart pointers and was trying to refactor some existing code to use auto_ptr. The question I have is about double pointers and their auto_ptr equivalent, if that makes sense. I have a function that accepts a double pointer as its parameter and the function allocates resources for it: void foo ( Image** img ) { ... *img = new Image(); ...} This function is then used like this: Image* img = NULL; foo ( &img ); ... delete img; I want to use auto_ptr to avoid having to call delete explicitly. Is the following correct? void foo ( auto_ptr<Image>* img ); and then auto_ptr<Image> img = NULL; foo ( &img ); Thanks.

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  • Conversion of pointer-to-pointer between derived and base classes?

    - by Mike Mueller
    Regarding the following C++ program: class Base { }; class Child : public Base { }; int main() { // Normal: using child as base is allowed Child *c = new Child(); Base *b = c; // Double pointers: apparently can't use Child** as Base** Child **cc = &c; Base **bb = cc; return 0; } GCC produces the following error on the last assignment statement: error: invalid conversion from ‘Child**’ to ‘Base**’ My question is in two parts: Why is there no implicit conversion from Child** to Base**? I can make this example work with a C-style cast or a reinterpret_cast. Using these casts means throwing away all type safety. Is there anything I can add to the class definitions to make these pointers cast implicitly, or at least phrase the conversion in a way that allows me to use static_cast instead?

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  • Arrow operator (->) usage in C

    - by Mohit Deshpande
    I am currently learning C by reading a good beginner's book called "Teach Yourself C in 21 Days" (I have already learned Java and C# so I am moving at a much faster pace). I was reading the chapter on pointers and the - (arrow) operator came up without explanation. I think that it is used to call members and functions (like the equivalent of the . (dot) operator, but for pointers instead of members). But I am not entirely sure. Could I please get an explanation and a code sample?

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  • C# huge size 2-dim arrays

    - by 4eburek
    I need to declare square matrices in C# WinForms with more than 20000 items in a row. I read about 2GB .Net object size limit in 32bit and also the same case in 64bit OS. So as I understood the single answer - is using unsafe code or separate library built withing C++ compiler. The problem for me is worth because ushort[20000,20000] is smaller then 2GB but actually I cannot allocate even 700MB of memory. My limit is 650MB and I don't understand why - I have 32bit WinXP with 3GB of memory. I tried to use Marshal.AllocHGlobal(700<<20) but it throws OutOfMemoryException, GC.GetTotalMemory returns 4.5MB before trying to allocate memory. I found only that many people say use unsafe code but I cannot find example of how to declare 2-dim array in heap (any stack can't keep so huge amount of data) and how to work with it using pointers. Is it pure C++ code inside of unsafe{} brackets? Could you please provide a small example of working with matrices using pointers in unsafe code.

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  • Why implement DB connection pointer object as a reference counting pointer? (C++)

    - by DVK
    At our company one of the core C++ classes (Database connection pointer) is implemented as a reference counting pointer. To be clear, the objects are NOT DB connections themselves, but pointers to a DB connection object. The library is very old, and nobody who designed is around anymore. So far, nether I, nor any C++ experts in the company that I asked have come up with a good reason for why this particular design was chosen. Any ideas? It is introducing some problems (partially due to awful reference pointer implementation used), and I'm trying to understand if this design actually has some deep underlying reasons? The usage pattern these days seems to be that the DB connection pointer object is returned by a DB connection manager class, and it's somewhat unclear whether DB connection pointers were designed to be able to be used independently of DB connection manager.

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  • Array of strings and char ** environ variable.

    - by Naruto Uzumaki
    Hello! I want to know how an array of strings is declared? What I do is I declare an array of pointers of pointers to strings. Eg. char *array[]= {"string1","string2","string3"}; I was reading about modifying environment variables in Linux and stumbled upon the pointer char **environ ( http://www.cs.bham.ac.uk/resources/courses/2005/17423/doc/libc/Environment-Access.html#Environment-Access ). char **environ is declared as an array of strings. I think it should be a pointer to a pointer. For eg. char *array[]= {"string1","string2","string3"}; environ = array; Am I doing something wrong? I also read somewhere that char *argv[] = char **argv. How is it possible?

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  • Safe to cast pointer to a forward-declared class to its true base class in C++?

    - by Matt DiMeo
    In one header file I have: #include "BaseClass.h" // a forward declaration of DerivedClass, which extends class BaseClass. class DerivedClass ; class Foo { DerivedClass *derived ; void someMethod() { // this is the cast I'm worried about. ((BaseClass*)derived)->baseClassMethod() ; } }; Now, DerivedClass is (in its own header file) derived from BaseClass, but the compiler doesn't know that at the time it's reading the definition above for class Foo. However, Foo refers to DerivedClass pointers and DerivedClass refers to Foo pointers, so they can't both know each other's declaration. First question is whether it's safe (according to C++ spec, not in any given compiler) to cast a derived class pointer to its base class pointer type in the absence of a full definition of the derived class. Second question is whether there's a better approach. I'm aware I could move someMethod()'s body out of the class definition, but in this case it's important that it be inlined (part of an actual, measured hotspot - I'm not guessing).

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  • C++ Pointer Issue

    - by Winder
    _stuckVertices is an array of pointers and I would like to update one index of that array without using _stuckVertices[ (row * _cols) + column ] 3 times. The reason it is an array of pointers is because the vast majority of the time the pointer will be NULL. The following code works but I need to dereference a each time I use it: void Cloth::stickPoint(int column, int row) { Anchor **a = &_stuckVertices[ (row * _cols) + column ]; if (!*a) *a = new Anchor(this, column, row); (*a)->stick(); } I originally had it written like this, but the _stuckVertices pointer doesn't get updated: void Cloth::stickPoint(int column, int row) { Anchor *a = _stuckVertices[ (row * _cols) + column ]; if (!a) a = new Anchor(this, column, row); a->stick(); } Is there a way to write Anchor *a = _stuckVertices[ index ] so that a is like an alias into the array that I can update, or is something like the first piece of code how I should do this? Thanks

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