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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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  • c++0x, std::thread error (thread not member of std)

    - by luis
    Hello I compiled & installed gcc4.4 using macports. When I try to compile using - g++ -g -Wall -ansi -pthread -std=c++0x main.cpp...: #include ... std::thread t(handle); t.join(); .... The compiler returns: cserver.cpp: In member function 'int CServer::run()': cserver.cpp:48: error: 'thread' is not a member of 'std' cserver.cpp:48: error: expected ';' before 't' cserver.cpp:49: error: 't' was not declared in this scope But std::cout <<... compiles fine.. Can anyone help me? Thanks! Luis

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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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  • F# Static Member Type Constraints

    - by Stephen Swensen
    I'm trying to define a function, factorize, which uses structural type constraints (requires static members Zero, One, +, and /) similar to Seq.sum so that it can be used with int, long, bigint, etc. I can't seem to get the syntax right, and can't find a lot of resources on the subject. This is what I have, please help. let inline factorize (n:^NUM) = ^NUM : (static member get_Zero: unit->(^NUM)) ^NUM : (static member get_One: unit->(^NUM)) let rec factorize (n:^NUM) (j:^NUM) (flist: ^NUM list) = if n = ^NUM.One then flist elif n % j = ^NUM.Zero then factorize (n/j) (^NUM.One + ^NUM.One) (j::flist) else factorize n (j + ^NUM.One) (flist) factorize n (^NUM.One + ^NUM.One) []

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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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  • convert pointer to pointer to void pointer

    - by FihopZz
    When I'm learning to use qsort to sort an array of string, there is a question puzzled me. For example, to sort the following s char *s[] = { "Amit", "Garima", "Gaurav", "Vaibhav" }; To use the qsort, you must provide a comparison function like the following function cstring_cmp I guess in the qsort function, the type of parameter to be passed to the function cstring_cmp is char**. How to convert a char** to a void*? Why can we convert a char** to a void*? int cstring_cmp(const void *a, const void *b) { const char **ia = (const char **)a; const char **ib = (const char **)b; return -strcasecmp(*ia, *ib); /* return the negative of the normal comparison */ }

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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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  • Objective-C member variable assignment?

    - by Alex
    I have an objective-c class with member variables. I am creating getters and setters for each one. Mostly for learning purposes. My setter looks like the following: - (void) setSomething:(NSString *)input { something = input; } However, in C++ and other languages I have worked with in the past, you can reference the member variable by using the this pointer like this->something = input. In objective-c this is known as self. So I was wondering if something like that is possible in objective-c? Something like this: - (void) setSomething:(NSString *)input { [self something] = input; } But that would call the getter for something. So I'm not sure. So my question is: Is there a way I can do assignment utilizing the self pointer? If so, how? Is this good practice or is it evil? 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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  • conflicting declaration when filling a static std::map class member variable

    - by Max
    I have a class with a static std::map member variable that maps chars to a custom type Terrain. I'm attempting to fill this map in the class's implementation file, but I get several errors. Here's my header file: #ifndef LEVEL_HPP #define LEVEL_HPP #include <bitset> #include <list> #include <map> #include <string> #include <vector> #include "libtcod.hpp" namespace yarl { namespace level { class Terrain { // Member Variables private: std::bitset<5> flags; // Member Functions public: explicit Terrain(const std::string& flg) : flags(flg) {} (...) }; class Level { private: static std::map<char, Terrain> terrainTypes; (...) }; } } #endif and here's my implementation file: #include <bitset> #include <list> #include <map> #include <string> #include <vector> #include "Level.hpp" #include "libtcod.hpp" using namespace std; namespace yarl { namespace level { /* fill Level::terrainTypes */ map<char,Terrain> Level::terrainTypes['.'] = Terrain("00001"); // clear map<char,Terrain> Level::terrainTypes[','] = Terrain("00001"); // clear map<char,Terrain> Level::terrainTypes['\''] = Terrain("00001"); // clear map<char,Terrain> Level::terrainTypes['`'] = Terrain("00001"); // clear map<char,Terrain> Level::terrainTypes[178] = Terrain("11111"); // wall (...) } } I'm using g++, and the errors I get are src/Level.cpp:15: error: conflicting declaration ‘std::map, std::allocator yarl::level::Level::terrainTypes [46]’ src/Level.hpp:104: error: ‘yarl::level::Level::terrainTypes’ has a previous declaration as ‘std::map, std::allocator yarl::level::Level::terrainTypes’ src/Level.cpp:15: error: declaration of ‘std::map, std::allocator yarl::level::Level::terrainTypes’ outside of class is not definition src/Level.cpp:15: error: conversion from ‘yarl::level::Terrain’ to non-scalar type ‘std::map, std::allocator ’ requested src/Level.cpp:15: error: ‘yarl::level::Level::terrainTypes’ cannot be initialized by a non-constant expression when being declared I get a set of these for each map assignment line in the implementation file. Anyone see what I'm doing wrong? Thanks for your help.

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  • pointer to member function question

    - by Steve
    Hello, I'm trying to replicate a template I've used before with a member function, and it isn't going very well. The basic form of the function is template<class T> T Convert( HRESULT (*Foo)(T*)) { T temp; Foo(&temp); //Throw if HRESULT is a failure return temp; } HRESULT Converter(UINT* val) { *val = 1; return S_OK; } int _tmain(int argc, _TCHAR* argv[]) { std::cout << Convert<UINT>(Converter) << std::endl; return 0; } For the life of me, I can't get this to work with a member variable. I've read up on their syntax, and I can't seem to figure out how to make it work with templates. The class would be something similar to class TestClass { HRESULT Converter(UINT* val) { *val = 1; return S_OK; } }

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  • C++ smart pointer for a non-object type?

    - by Brian
    Hi, I'm trying to use smart pointers such as auto_ptr, shared_ptr. However, I don't know how to use it in this situation. CvMemStorage *storage = cvCreateMemStorage(); ... use the pointer ... cvReleaseMemStorage(&storage); I'm not sure, but I think that the storage variable is just a malloc'ed memory, not a C++ class object. Is there a way to use the smart pointers for the storage variable? Thank you.

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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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  • F# static member

    - by HeMan
    I was working through the PDC 2008 F# videos and seem to run into a problem type StockAnalyzer (lprices, days) = let prices = lprices | Seq.map snd | Seq.take days static member GetAnalyzers(tickers, days) = tickers | Seq.map loadPrices | Seq.map (fun prices - new StockAnalyzer(prices, days)) member s.Return = let lastPrice = prices |> Seq.nth 0 let startPrice = prices |> Seq.nth (days - 1) lastPrice / startPrice - 1. I am getting an error at the static. GetStockPrices.fs(31,6): error FS0010: Unexpected keyword 'static' in binding. Expected incomplete structured construct at or before this point or other token. Does anyone know if they have changed the syntax or can spot what I am doing wrong

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  • C++ smart pointer for non-object type?

    - by Brian
    Hi, I'm trying to use smart pointers such as auto_ptr, shared_ptr. However, I don't know how to use it in this situation. CvMemStorage *storage = cvCreateMemStorage(); ... use the pointer ... cvReleaseMemStorage(&storage); I'm not sure, but I think that the storage variable is just malloc'ed memory, not object. Is there a way to use the smart pointers for the storage variable? Thank you.

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  • STL Static-Const Member Definitions

    - by javery
    How does the following work? #include <limits> int main() { const int* const foo = &std::numeric_limits<int> ::digits; } I was under the impression that in order to take an address of a static const-ant member we had to physically define it in some translation unit in order to please the linker. That said, after looking at the preprocessed code for this TU, I couldn't find an external definition for the digits member (or any other relevant members). I tested this on two compilers (VC++ 10 and g++ 4.2.4) and got identical results (i.e., it works). Does the linker auto-magically link against an object file where this stuff is defined, or am I missing something obvious here?

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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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  • What effect does static const have on a namespace member

    - by user144182
    namespace MyNamespace { static const double GasConstant = 1.987; Class MyClass { // constructors, methods, etc. }; }; I previously had GasConstant declared within the MyClass declaration (and had a separate definition in the source file since C++ does not support const initialization of non-integral types). I however need to access it from other files and also logically it seems like it should reside at the namespace level. My questions is, what effect does static const have in this case? Clearly const means I can't assign a new value to GasConstant, but what does a static member at the namespace mean. Is this similar to filescope static effect, where the member is not accessible outside of the unit?

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  • inline and member initializers

    - by Alexander
    When should I inline a member function and when should I use member initializers? My code is below.. I would like to modify it so I could make use some inline when appropriate and member initializers: #include "Books.h" Book::Book(){ nm = (char*)""; thck = 0; wght = 0; } Book::Book(const char *name, int thickness, int weight){ nm = strdup(name); thck = thickness; wght = weight; } Book::~Book(){ } const char* Book::name(){ return nm; } int Book::thickness(){ return thck; } int Book::weight(){ return wght; } // // Prints information about the book using this format: // "%s (%d mm, %d dg)\n" // void Book::print(){ printf("%s (%d mm, %d dg)\n", nm, thck, wght); } Bookcase::Bookcase(int id){ my_id = id; no_shelf = 0; } int Bookcase::id(){ return my_id; } Bookcase::~Bookcase(){ for (int i = 0; i < no_shelf; i++) delete my_shelf[i]; } bool Bookcase::addShelf(int width, int capacity){ if(no_shelf == 10) return false; else{ my_shelf[no_shelf] = new Shelf(width, capacity); no_shelf++; return true; } } bool Bookcase::add(Book *bp){ int index = -1; int temp_space = -1; for (int i = 0; i < no_shelf; i++){ if (bp->weight() + my_shelf[i]->curCapacity() <= my_shelf[i]->capacity()){ if (bp->thickness() + my_shelf[i]->curWidth() <= my_shelf[i]->width() && temp_space < (my_shelf[i]->width() - my_shelf[i]->curWidth())){ temp_space = (my_shelf[i]->width()- my_shelf[i]->curWidth()); index = i; } } } if (index != -1){ my_shelf[index]->add(bp); return true; }else return false; } void Bookcase::print(){ printf("Bookcase #%d\n", my_id); for (int i = 0; i < no_shelf; i++){ printf("--- Shelf (%d mm, %d dg) ---\n", my_shelf[i]->width(), my_shelf[i]->capacity()); my_shelf[i]->print(); } }

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  • STL member variable initalization issue with windows API

    - by Django
    I am creating a windows app that uses a vector of stings as a member variable. For some reason, I can compile but when it tries to get at any of the vectors members is crashes. the error is 0xC0000005: Access violation reading location 0xcdcdcdd9. in the member function of the vector class. this is the size() function where it breaks. size_type capacity() const { // return current length of allocated storage return (this->_Myend - this->_Myfirst); } I am using visual studios 2010. thank you Django

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