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  • Using a type parameter and a pointer to the same type parameter in a function template

    - by Darel
    Hello, I've written a template function to determine the median of any vector or array of any type that can be sorted with sort. The function and a small test program are below: #include <algorithm> #include <vector> #include <iostream> using namespace::std; template <class T, class X> void median(T vec, size_t size, X& ret) { sort(vec, vec + size); size_t mid = size/2; ret = size % 2 == 0 ? (vec[mid] + vec[mid-1]) / 2 : vec[mid]; } int main() { vector<double> v; v.push_back(2); v.push_back(8); v.push_back(7); v.push_back(4); v.push_back(9); double a[5] = {2, 8, 7, 4, 9}; double r; median(v.begin(), v.size(), r); cout << r << endl; median(a, 5, r); cout << r << endl; return 0; } As you can see, the median function takes a pointer as an argument, T vec. Also in the argument list is a reference variable X ret, which is modified by the function to store the computed median value. However I don't find this a very elegant solution. T vec will always be a pointer to the same type as X ret. My initial attempts to write median had a header like this: template<class T> T median(T *vec, size_t size) { sort(vec, vec + size); size_t mid = size/2; return size % 2 == 0 ? (vec[mid] + vec[mid-1]) / 2 : vec[mid]; } I also tried: template<class T, class X> X median(T vec, size_t size) { sort(vec, vec + size); size_t mid = size/2; return size % 2 == 0 ? (vec[mid] + vec[mid-1]) / 2 : vec[mid]; } I couldn't get either of these to work. My question is, can anyone show me a working implementation of either of my alternatives? Thanks for looking!

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  • Pointer-Safe Objects?

    - by cam
    Would it be smart to have a vector in an object with a list of pointers that point to it? This way when the object is deleted, it could delete all the pointers pointing to it to prevent a null-pointer exception?

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  • Smart pointer class predeclaration

    - by tommyk
    I have a header file: class A { public: DeviceProxyPtr GetDeviceProxy(); }; DeviceProxyPtr is defined in a different header file like this: typedef SmartPtrC<DeviceProxyC> DeviceProxyPtr; I don't want to include DeviceProxyPtr definition header. If a return type was DeviceProxy* I could simply use predeclaration class DeviceProxy. Is there any way to do the same with my smart pointer class?

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  • Another warning question: "Incompatible intiger to pointer conversion assigning to 'int *' from 'int'"

    - by Preston
    I have yet another pesky warning I would like gone. Basically, I have an int declared like this: @property (nonatomic, assign) int *myInt; and set like this: myInt = 0;. It is also synthesized in the implementation file. I am getting a warning on the line where I set the int's value and it says "Incompatible intiger to pointer conversion assigning to 'int *' from 'int'." What should I do to fix this?

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  • Dangling pointer

    - by viswanathan
    How can the below code result in a dangling pointer. { char *cPointer = malloc ( some constant number ); /* some code */ free ( cPointer ); cPointer = NULL; /* some code */ }

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  • How can I declare a pointer structure?

    - by Y_Y
    This probably is one of the easiest questions ever in C programming language... I have the following code: typedef struct node { int data; struct node * after; struct node * before; }node; struct node head = {10,&head,&head}; Is there a way I can make head to be *head [make it a pointer] and still have the availability to use '{ }' [{10,&head,&head}] to declare an instance of head?

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  • Why is dereferencing a pointer called dereferencing?

    - by optician
    Why is dereferencing called dereferencing? I'm just learning pointers properly, and I'd like to know why dereferencing is called that. It confused me as it sounds like you are removing a reference, rather than going via the pointer to the destination. Can anyone explain why it is called this? To me something like destination or pointed_to_value would make more sense.

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  • C++ using this pointer in constructors

    - by gilbertc
    In c++, during a class constructor, I started a new thread with 'this' pointer as a parameter which will be used in the thread extensively (say, calling member functions). Is that a bad thing to do? Why and what are the consequences? Thanks, Gil.

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  • Advice on "Invalid Pointer Operation" when using complex records

    - by Xaz
    Env: Delphi 2007 <JustificationI tend to use complex records quite frequently as they offer almost all of the advantages of classes but with much simpler handling.</Justification Anyhoo, one particularly complex record I have just implemented is trashing memory (later leading to an "Invalid Pointer Operation" error). This is an example of the memory trashing code: sSignature := gProfiles.Profile[_stPrimary].Signature.Formatted(True); On the second time i call it i get "Invalid Pointer Operation" It works OK if i call it like this: AProfile := gProfiles.Profile[_stPrimary]; ASignature := AProfile.Signature; sSignature := ASignature.Formatted(True); Background Code: gProfiles: TProfiles; TProfiles = Record private FPrimaryProfileID: Integer; FCachedProfile: TProfile; ... public < much code removed > property Profile[ProfileType: TProfileType]: TProfile Read GetProfile; end; function TProfiles.GetProfile(ProfileType: TProfileType): TProfile; begin case ProfileType of _stPrimary : Result := ProfileByID(FPrimaryProfileID); ... end; end; function TProfiles.ProfileByID(iID: Integer): TProfile; begin <snip> if LoadProfileOfID(iID, FCachedProfile) then begin Result := FCachedProfile; end else ... end; TProfile = Record private ... public ... Signature: TSignature; ... end; TSignature = Record private public PlainTextFormat : string; HTMLFormat : string; // The text to insert into a message when using this profile function Formatted(bHTML: boolean): string; end; function TSignature.Formatted(bHTML: boolean): string; begin if bHTML then result := HTMLFormat else result := PlainTextFormat; < SNIP MUCH CODE > end; OK, so I have a record within a record within a record, which is approaching Inception level confusion and I'm the first to admit is not really a good model. Clearly i am going to have to restructure it. What I would like from you gurus is a better understanding of why it is trashing the memory (something to do with the string object that is created then freed...) so that i can avoid making these kinds of errors in future. Thanks

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  • Passing a pointer to a function in objective-c

    - by Chiodo
    Hi, i've a stupid questiona about passing pointer. I've this: @interface MyClass : NSObject myobj* foo; -(void)doSomething:(myobj*)aObj; @end @implementation MyClass -(void)doSomething:(myobj*)aObj { cFuncCall(&aObj); //alloc memory and init the object } -(id)init { //init stuff... [self doSomething:foo]; // foo retun 0x0!!! } @end why foo return nil??? It should be initialized by cFuncCall!

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  • Pass a pointer to a proc as an argument

    - by user146780
    I want to pass a pointer to a procedure in c++. I tried passing this LRESULT(*)(HWND, UINT, WPARAM, LPARAM) prc but it didn't work. How is this done? Thanks HWND OGLFRAME::create(HWND parent, LRESULT(*)(HWND, UINT, WPARAM, LPARAM) prc) { if(framehWnd != NULL) { return framehWnd; ZeroMemory(&rwc,sizeof(rwc)); } } By "it didn't work" I mean it's a syntax error.

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  • Incompatible pointer type

    - by Boffin
    Hello. I have the function with following signature: void box_sort(int**, int, int) and variable of following type: int boxes[MAX_BOXES][MAX_DIMENSIONALITY+1] When I am calling the function box_sort(boxes, a, b) GCC gives me two warnings: 103.c:79: warning: passing argument 1 of ‘box_sort’ from incompatible pointer type (string where i am calling the function) 103.c:42: note: expected ‘int **’ but argument is of type ‘int (*)[11] (string where the function is defined) The question is why? Whether int x[][] and int** x (and actually int* x[]) are not the same types in C?

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  • C++ finding pointer errors

    - by Tony
    Hello! I am currently on a project which has been buggy for a long while, now I suspect, among other things, that there is pointer errors in the code. The program is written in native C++ using COM and uses out-of-process COM servers. Can anybody give me some tips as how one would go about finding these errors? Is there specific things to keep in mind, ways to do it, etc...

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  • pointer to preallocated memory as an input parameter and have the function fill it

    - by djones2010
    test code: void modify_it(char * mystuff) { char test[7] = "123456"; //last element is null i presume for c style strings here. //static char test[] = "123123"; //when i do this i thought i should be able to gain access to this bit of memory when the function is destroyed but that does not seem to be the case. //char * test = new char[7]; //this is also creating memory on stack and not the heap i reckon and gets destroyed once the function is done with. strcpy_s(mystuff,7,test); //this does the job as long as memory for mystuff has been allocated outside the function. mystuff = test; //this does not work. I know with c style strings you can't just do string assignments they have to be actually copied. in this case I was using this in conjunction with static char test thinking by having it as static the memory would not get destroyed and i can then simply point mystuff to test and be done with it. i would later have address the memory cleanup in the main function. but anyway this never worked. } int main(void) { char * mystuff = new char [7]; //allocate memory on heap where the pointer will point cool(mystuff); std::string test_case(mystuff); std::cout<<test_case.c_str(); //this is the only way i know how to use cout by making it into a string c++ string. delete [] mystuff; return 0; } in the case, of a static array in the function why would it not work. in the case, when i allocated memory using new in the function does it get created on the stack or heap? in the case, i have string which needs to be copied into a char * form. everything i see usually requires const char* instead of just char*. I know i could use reference to take care of this easy. Or char ** to send in the pointer and do it that way. But i just wanted to know if I could do it with just char *. Anyway your thoughts and comments plus any examples would be very helpful.

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  • Where to put the star in C and C++ pointer notation

    - by Martin Kristiansen
    For some time the following has been annoing me, where should I put the star in my pointer notation. int *var; // 1 and int* var; // 2 obviously do the same thing, and both notations are correct, but I find that most literature and code I look at use the 1th notation. wouldn't it be more 'correct' to use the 2th notation, separating the type and the variable name by a whitespace, rather than mixing the type and variable tokens?

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