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  • Void pointers in C

    - by avd
    I have written this qsort: void qsort(void *a[],int low,int high, int (*compare)(void*,void*)); When I call this on char *strarr[5]; It says invalid conversion from char** to void**. Why this is wrong? This is the code:http://codepad.org/Flfm2zAE

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  • C++ Pointers, objects, etc

    - by Zeee
    It may be a bit confusing, but... Let's say I have a vector type in a class to store objects, something like vector, and I have methods on my class that will later return Operators from this vector. Now if any of my methods receives an Operator, will I have any trouble to insert it directly into the vector? Or should I use the copy constructor to create a new Operator and put this new one on the vector?

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  • Vector of pointers to base class, odd behaviour calling virtual functions

    - by Ink-Jet
    I have the following code #include <iostream> #include <vector> class Entity { public: virtual void func() = 0; }; class Monster : public Entity { public: void func(); }; void Monster::func() { std::cout << "I AM A MONSTER" << std::endl; } class Buddha : public Entity { public: void func(); }; void Buddha::func() { std::cout << "OHMM" << std::endl; } int main() { const int num = 5; // How many of each to make std::vector<Entity*> t; for(int i = 0; i < num; i++) { Monster m; Entity * e; e = &m; t.push_back(e); } for(int i = 0; i < num; i++) { Buddha b; Entity * e; e = &b; t.push_back(e); } for(int i = 0; i < t.size(); i++) { t[i]->func(); } return 0; } However, when I run it, instead of each class printing out its own message, they all print the "Buddha" message. I want each object to print its own message: Monsters print the monster message, Buddhas print the Buddha message. What have I done wrong?

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  • array of pointers

    - by tushar
    char *a[]={"diamonds","clubs","spades","hearts"}; char **p[]={a+3,a+2,a+1,a}; char ***ptr=p; cout<<*ptr[2][2]; why does it display h and please explain how is the 2d array of ptr implementing and its elements

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  • Member variable pointers to COM objects

    - by drelihan
    Hi Folks, Is there any problem with keeping member variable pointer refernces to COM objects and reussing the reference through out the class in C++. Is anybody aware of a reason why you would want to call .CreateInstance every time you wanted a to use the COM object i.e. you were getting a fresh instance each time. I cannot see any reason who you would want to do this, Thanks, (No is an acceptable answer!!!)

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  • Accessing structure elements using pointers

    - by Arun Nadesh
    Hi Everybody, Greetings! I got surprised when the following program did not crash. typedef struct _x{ int a; char b; int c; }x; main() { x *ptr=0; char *d=&ptr->b; } As per my understanding the -> operator has higher precedence over & operator. So I expected the program to crash at the below statement when we try to dereference the NULL pointer tr. char *d=&ptr->b; But the statement &ptr->b evaluates to a valid address. Could somebody please explain where I'm wrong? Thanks & Regards, Arun

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  • Arrays of pointers to arrays?

    - by a2h
    I'm using a library which for one certain feature involves variables like so: extern const u8 foo[]; extern const u8 bar[]; I am not allowed to rename these variables in any way. However, I like to be able to access these variables through an array (or other similar method) so that I do not need to continually hardcode new instances of these variables into my main code. My first attempt at creating an array is as follows: const u8* pl[] = { &foo, &bar }; This gave me the error cannot convert 'const u8 (*)[]' to 'const u8*' in initialization, and with help elsewhere along with some Googling, I changed my array to this: u8 (*pl)[] = { &foo, &bar }; Upon compiling I now get the error scalar object 'pl' requires one element in initializer. Does anyone have any ideas on what I'm doing wrong? Thanks.

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  • How to handle an array of pointers in Objective-C

    - by DougW
    I figured out the answer to this question, but I couldn't find the solution on here, so posting it for posterity. So, in Objective-C, how do you create an object out of a pointer in order to store it in objective-c collections (NSArray, NSDictionary, NSSet, etc) without reverting to regular C?

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  • Throwing Exception in CTOR and Smart Pointers

    - by David Relihan
    Is it OK to have the following code in my constructor to load an XML document into a member variable - throwing to caller if there are any problems: MSXML2::IXMLDOMDocumentPtr m_docPtr; //member Configuration() { try { HRESULT hr = m_docPtr.CreateInstance(__uuidof(MSXML2::DOMDocument40)); if ( SUCCEEDED(hr)) { m_docPtr->loadXML(CreateXML()); } else { //throw exception to caller } } catch(...) { //throw exception to caller } } Based on Scott Myers RAII implementations in More Effective C++ I believe I am alright in just allowing exceptions to be thrown from CTOR as I am using a smart pointer(IXMLDOMDocumentPtr). Let me know what you think....

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  • Help with pointers in Cocoa

    - by G.P. Burdell
    I'm trying to make a simple calculator application in cocoa. The program hangs when I click on one of my buttons. I think I've traced the problem to the part of my controller that adds a digit to the end of the number currently on the display: - (void)updateNumber:(int)buttonClicked{ *self.activeNumberPointer = *self.activeNumberPointer * 10 + buttonClicked; [outputField setFloatValue:*self.activeNumberPointer]; } I used a pointer to the "activeNumber" in order to allow my program to tell which of the two operands I'm editing. Any help appreciated, thanks.

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  • COM Pointers and process termination

    - by Tony
    Can an unreleased COM pointer to an external process (still alive) cause that process to hang on destruction? Even with TerminateProcess called on it? Process A has a COM interface pointer reference to Process B, now Process B issues a TerminateProcess on A, if some COM interface pointer to Process B in Process A is not released properly, could it be that the process hangs on termination?

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  • Pointers in C# to make int array?

    - by Joshua
    The following C++ program compiles and runs as expected: #include <stdio.h> int main(int argc, char* argv[]) { int* test = new int[10]; for (int i = 0; i < 10; i++) test[i] = i * 10; printf("%d \n", test[5]); // 50 printf("%d \n", 5[test]); // 50 return getchar(); } The closest C# simple example I could make for this question is: using System; class Program { unsafe static int Main(string[] args) { // error CS0029: Cannot implicitly convert type 'int[]' to 'int*' int* test = new int[10]; for (int i = 0; i < 10; i++) test[i] = i * 10; Console.WriteLine(test[5]); // 50 Console.WriteLine(5[test]); // Error return (int)Console.ReadKey().Key; } } So how do I make the pointer?

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  • Vectors of Pointers, inheritance

    - by user308553
    Hi I am a C++ beginner just encountered a problem I don't know how to fix I have two class, this is the header file: class A { public: int i; A(int a); }; class B: public A { public: string str; B(int a, string b); }; then I want to create a vector in main which store either class A or class B vector<A*> vec; A objectOne(1); B objectTwo(2, "hi"); vec.push_back(&objectOne); vec.push_back(&objectTwo); cout << vec.at(1)->i; //this is fine cout << vec.at(1)->str; //ERROR here I am really confused, I checked sites and stuff but I just don't know how to fix it, please help thanks in advance

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  • STL Vectors, pointers and classes

    - by anubis9
    Hey! Let's say i have 2 classes: class Class1 { public: std::vector<CustomClass3*> mVec; public: Class1(); ~Class1() { //iterate over all the members of the vector and delete the objects } }; class InitializerClass2 { private: Class1 * mPtrToClass1; public: InitializerClass2(); void Initialize() { mPtrToClass1->mVec.push_back(new CustomClass3(bla bla parameters)); } }; Will this work? Or the memory allocated in the InitializerClass2::Initialize() method might get corrupted after the method terminates? Thanks!

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  • An array of LPWSTR pointers, not working right.

    - by BigBirdy
    Declare: LPWSTR** lines= new LPWSTR*[totalLines]; then i set using: lines[totalLines]=&totalText; SetWindowText(totalChat,(LPWSTR)lines[totalLines]); totalLines++; Now I know totalText is right, cause if i SetWindowText using totalText it works fine. I need the text in totalLines too. I'm also doing: //accolating more memory. int orgSize=size; LPWSTR** tempArray; if (totalLines == size) { size *= 2; tempArray = new LPWSTR*[size]; memcpy(tempArray, lines,sizeof(LPWSTR)*orgSize); delete [] lines; lines = tempArray; } to allocate more memory when needed. My problem is that the lines is not getting the right data. It works for the first time around then it get corrupted. I thought at first i was overwriting but totalLines is increase. Hopefully this is enough information.

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  • Copy constructor, objects, pointers

    - by Pauff
    Let's say I have this: SolutionSet(const SolutionSet &solutionSet) { this->capacity_ = solutionSet.capacity_; this->solutionsList_ = solutionSet.solutionsList_; // <-- } And solutionsList_ is a vector<SomeType*> vect*. What is the correct way to copy that vector (I suppose that way I'm not doing it right..)?

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  • Problem with pointers

    - by noname
    OK, i have a strange problem. I have this piece of code: int *p; int test; p=&test; In Visual C++ express, in my exsisting project, I get this error: missing type specifier - int assumed. 'p' : 'int' differs in levels of indirection from 'char *' 'initializing' : cannot convert from 'char *' to 'int' But when i create new project, same code is fine. Whats the problem please?

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  • Using pointers to adjust global objects in objective-c

    - by Rob
    Ok, so I am working with two sets of data that are extremely similar, and at the same time, these data sets are both global NSMutableArrays within the object. data_set_one = [[NSMutableArray alloc] init]; data_set_two = [[NSMutableArray alloc] init]; Two new NSMutableArrays are loaded, which need to be added to the old, existing data. These Arrays are also global. xml_dataset_one = [[NSMutableArray alloc] init]; xml_dataset_two = [[NSMutableArray alloc] init]; To reduce code duplication (and because these data sets are so similar) I wrote a void method within the class to handle the data combination process for both Arrays: -(void)constructData:(NSMutableArray *)data fromDownloadArray:(NSMutableArray *)down withMatchSelector:(NSString *)sel_str Now, I have a decent understanding of object oriented programming, so I was thinking that if I were to invoke the method with the global Arrays in the data like so... [self constructData:data_set_one fromDownloadArray:xml_dataset_one withMatchSelector:@"id"]; Then the global NSMutableArrays (data_set_one) would reflect the changes that happen to "array" within the method. Sadly, this is not the case, data_set_one doesn't reflect the changes (ex: new objects within the Array) outside of the method. Here is a code snippet of the problem // data_set_one is empty // xml_dataset_one has a few objects [constructData:(NSMutableArray *)data_set_one fromDownloadArray:(NSMutableArray *)xml_dataset_one withMatchSelector:(NSString *)@"id"]; // data_set_one should now be xml_dataset_one, but when echoed to screen, it appears to remain empty And here is the gist of the code for the method, any help is appreciated. -(void)constructData:(NSMutableArray *)data fromDownloadArray:(NSMutableArray *)down withMatchSelector:(NSString *)sel_str { if ([data count] == 0) { data = down; // set data equal to downloaded data } else if ([down count] == 0) { // download yields no results, do nothing } else { // combine the two arrays here } } This project is not ARC enabled. Thanks for the help guys! Rob

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  • For-Each and Pointers in Java

    - by John
    Ok, so I'm tyring to iterate through an ArrayList and remove a specefic element. However, I am having some trouble using the For-Each like structure. When I run the following code: ArrayList<String> arr = new ArrayList<String>(); //... fill with some values (doesn't really matter) for(String t : arr) { t = " some other value "; //hoping this would change the actual array } for(String t : arr) { System.out.println(t); //however, I still get the same array here } My question in, how can I make 't' a pointer to 'arr' so that I am able to change the values in a for-each loop? I know I could loop through the ArrayList using a different structure, but this one looks so clean and readable, it would just be nice to be able to make 't' a pointer. All comments are appreciated! Even if you say I should just suck it up and use a different construct.

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  • C++: Trouble with Pointers, loop variables, and structs

    - by Rosarch
    Consider the following example: #include <iostream> #include <sstream> #include <vector> #include <wchar.h> #include <stdlib.h> using namespace std; struct odp { int f; wchar_t* pstr; }; int main() { vector<odp> vec; ostringstream ss; wchar_t base[5]; wcscpy_s(base, L"1234"); for (int i = 0; i < 4; i++) { odp foo; foo.f = i; wchar_t loopStr[1]; foo.pstr = loopStr; // wchar_t* = wchar_t ? Why does this work? foo.pstr[0] = base[i]; vec.push_back(foo); } for (vector<odp>::iterator iter = vec.begin(); iter != vec.end(); iter++) { cout << "Vec contains: " << iter->f << ", " << *(iter->pstr) << endl; } } This produces: Vec contains: 0, 52 Vec contains: 1, 52 Vec contains: 2, 52 Vec contains: 3, 52 I would hope that each time, iter->f and iter->pstr would yield a different result. Unfortunately, iter->pstr is always the same. My suspicion is that each time through the loop, a new loopStr is created. Instead of copying it into the struct, I'm only copying a pointer. The location that the pointer writes to is getting overwritten. How can I avoid this? Is it possible to solve this problem without allocating memory on the heap?

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  • C++ containers on classes, returning pointers

    - by otneil
    Hello, I'm having some trouble to find the best way to accomplish what I have in mind due to my inexperience. I have a class where I need to a vector of objects. So my first question will be: is there any problem having this: vector< AnyType container* and then on the constructor initialize it with new (and deleting it on the destructor)? Another question is: if this vector is going to store objects, shouldn't it be more like vector< AnyTipe* so they could be dynamically created? In that case how would I return an object from a method and how to avoid memory leaks (trying to use only STL)?

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  • Function pointers to member functions

    - by Jacob
    There are several duplicates of this but nobody explains why I can use a member variable to store the pointer (in FOO) but when I try it with a local variable (in the commented portion of BAR), it's illegal. Could anybody explain this? #include <iostream> using namespace std; class FOO { public: int (FOO::*fptr)(int a, int b); int add_stuff(int a, int b) { return a+b; } void call_adder(int a, int b) { fptr = &FOO::add_stuff; cout<<(this->*fptr)(a,b)<<endl; } }; class BAR { public: int add_stuff(int a, int b) { return a+b; } void call_adder(int a, int b) { //int (BAR::*fptr)(int a, int b); //fptr = &BAR::add_stuff; //cout<<(*fptr)(a,b)<<endl; } }; int main() { FOO test; test.call_adder(10,20); return 0; }

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  • Are pointers primitive types in C++?

    - by Space_C0wb0y
    I was wondering about the last constructor for std::string mentioned here. It says: template<class InputIterator> string (InputIterator begin, InputIterator end); If InputIterator is an integral type, behaves as the sixth constructor version (the one right above this) by typecasting begin and end to call it: string(static_cast<size_t>(begin),static_cast<char>(end)); In any other case, the parameters are taken as iterators, and the content is initialized with the values of the elements that go from the element referred by iterator begin to the element right before the one referred by iterator end. So what does that mean if InputIterator is a char * ?

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