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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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  • 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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  • Function pointers in Objective-C

    - by Stefan Klumpp
    I have the following scenario: Class_A - method_U - method_V - method_X - method_Y Class_B - method_M - method_N HttpClass - startRequest - didReceiveResponse // is a callback Now I want to realize these three flows (actually there are many more, but these are enough to demonstrate my question): Class_A :: method_X -> HttpClass :: startRequest:params -> ... wait, wait, wait ... -> HttpClass :: didReceiveResponse -> Class_A :: method_Y:result and: Class_A :: method_U -> HttpClass :: startRequest:params -> ... wait, wait, wait ... -> HttpClass :: didReceiveResponse -> Class_A :: method_V:result and the last one: Class_B :: method_M -> HttpClass :: startRequest:params -> ... wait, wait, wait ... -> HttpClass :: didReceiveResponse -> Class_B :: method_N:result Please note, that the methods in Class_A and Class_B have different names and functionality, they just make us of the same HttpClass. My solution now would be to pass a C function pointer to startRequest, store it in the HttpClass and when didReceiveResponse gets called I invoke the function pointer and pass the result (which will always be a JSON Dictionary). Now I'm wondering if there can be any problems using plain C or if there are better solutions doing it in a more Objective-C way. Any ideas?

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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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  • How does dereferencing of a function pointer happen?

    - by eSKay
    Why and how does dereferencing a function pointer just "do nothing"? This is what I am talking about: #include<stdio.h> void hello() { printf("hello"); } int main(void) { (*****hello)(); } From a comment over here: function pointers dereference just fine, but the resulting function designator will be immediately converted back to a function pointer And from an answer here: Dereferencing (in way you think) a function's pointer means: accessing a CODE memory as it would be a DATA memory. Function pointer isn't suppose to be dereferenced in that way. Instead, it is called. I would use a name "dereference" side by side with "call". It's OK. Anyway: C is designed in such a way that both function name identifier as well as variable holding function's pointer mean the same: address to CODE memory. And it allows to jump to that memory by using call () syntax either on an identifier or variable. How exactly does dereferencing of a function pointer work?

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  • Returning pointers in a thread-safe way.

    - by Roddy
    Assume I have a thread-safe collection of Things (call it a ThingList), and I want to add the following function. Thing * ThingList::findByName(string name) { return &item[name]; // or something similar.. } But by doing this, I've delegated the responsibility for thread safety to the calling code, which would have to do something like this: try { list.lock(); // NEEDED FOR THREAD SAFETY Thing *foo = list.findByName("wibble"); foo->Bar = 123; list.unlock(); } catch (...) { list.unlock(); throw; } Obviously a RAII lock/unlock object would simplify/remove the try/catch/unlocks, but it's still easy for the caller to forget. There are a few alternatives I've looked at: Return Thing by value, instead of a pointer - fine unless you need to modify the Thing Add function ThingList::setItemBar(string name, int value) - fine, but these tend to proliferate Return a pointerlike object which locks the list on creation and unlocks it again on destruction. Not sure if this is good/bad practice... What's the right approach to dealing with this?

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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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  • list of pointers in c++

    - by pavlos
    What i want to do is for (list<cPacket *>::iterator i = cache.begin(); i != cache.end(); i++){ if( strcmp(i->getName(),id) == 0 ){ return true; } } where getName is function of the class cPacket, But it does not work, i tries also i.operator->()->getName(), and again nothing. Can anybody help me?

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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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  • C++ pointers on example

    - by terence6
    I have a sample code : #include <iostream> #include <conio.h> using namespace std; int main () { int firstvalue = 5, secondvalue = 15; int * p1, * p2; p1 = &firstvalue; p2 = &secondvalue; cout << "1.p1: " << p1 << ", p2: " << p2 << endl; cout << "1.*p1: " << *p1 << ", *p2: " << *p2 << endl; *p1 = 10; cout << "2.p1: " << p1 << ", p2: " << p2 << endl; cout << "2.*p1: " << *p1 << ", *p2: " << *p2 << endl; *p2 = *p1; cout << "3.p1: " << p1 << ", p2: " << p2 << endl; cout << "3.*p1: " << *p1 << ", *p2: " << *p2 << endl; p1 = p2; cout << "4.p1: " << p1 << ", p2: " << p2 << endl; cout << "4.*p1: " << *p1 << ", *p2: " << *p2 << endl; *p1 = 20; cout << "5.p1: " << p1 << ", p2: " << p2 << endl; cout << "5.*p1: " << *p1 << ", *p2: " << *p2 << endl; cout << "firstvalue is " << firstvalue << endl; cout << "secondvalue is " << secondvalue << endl; cout << "firstvalue is " << &firstvalue << endl; cout << "secondvalue is " << &secondvalue << endl; getch(); return 0; } And here's the output : 1.p1: 0041FB40, p2: 0041FB34 1.*p1: 5, *p2: 15 2.p1: 0041FB40, p2: 0041FB34 2.*p1: 10, *p2: 15 3.p1: 0041FB40, p2: 0041FB34 3.*p1: 10, *p2: 10 4.p1: 0041FB34, p2: 0041FB34 4.*p1: 10, *p2: 10 5.p1: 0041FB34, p2: 0041FB34 5.*p1: 20, *p2: 20 firstvalue is 10 secondvalue is 20 firstvalue is 0041FB40 secondvalue is 0041FB34 What is copied in the line "p1 = p2" ? Does p1 become reference to p2 or does it work in different way ?

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  • Sort a list of pointers.

    - by YuppieNetworking
    Hello all, Once again I find myself failing at some really simple task in C++. Sometimes I wish I could de-learn all I know from OO in java, since my problems usually start by thinking like Java. Anyways, I have a std::list<BaseObject*> that I want to sort. Let's say that BaseObject is: class BaseObject { protected: int id; public: BaseObject(int i) : id(i) {}; virtual ~BaseObject() {}; }; I can sort the list of pointer to BaseObject with a comparator struct: struct Comparator { bool operator()(const BaseObject* o1, const BaseObject* o2) const { return o1->id < o2->id; } }; And it would look like this: std::list<BaseObject*> mylist; mylist.push_back(new BaseObject(1)); mylist.push_back(new BaseObject(2)); // ... mylist.sort(Comparator()); // intentionally omitted deletes and exception handling Until here, everything is a-ok. However, I introduced some derived classes: class Child : public BaseObject { protected: int var; public: Child(int id1, int n) : BaseObject(id1), var(n) {}; virtual ~Child() {}; }; class GrandChild : public Child { public: GrandChild(int id1, int n) : Child(id1,n) {}; virtual ~GrandChild() {}; }; So now I would like to sort following the following rules: For any Child object c and BaseObject b, b<c To compare BaseObject objects, use its ids, as before. To compare Child objects, compare its vars. If they are equal, fallback to rule 2. GrandChild objects should fallback to the Child behavior (rule 3). I initially thought that I could probably do some casts in Comparator. However, this casts away constness. Then I thought that probably I could compare typeids, but then everything looked messy and it is not even correct. How could I implement this sort, still using list<BaseObject*>::sort ? Thank you

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  • Pointers and Addresses in C

    - by Mohit
    #include "stdio.h" main() { int i=3,*x; float j=1.5,*y; char k='c',*z; x=&i; y=&j; z=&k; printf("\nAddress of x= %u",x); printf("\nAddress of y= %u",y); printf("\nAddress of z= %u",z); x++; y++;y++;y++;y++; z++; printf("\nNew Address of x= %u",x); printf("\nNew Address of y= %u",y); printf("\nNew Address of z= %u",z); printf("\nNew Value of i= %d",i); printf("\nNew Value of j= %f",j); printf("\nNew Value of k= %c\n",k); } Output: Address of x= 3219901868 Address of y= 3219901860 Address of z= 3219901875 New Address of x= 3219901872 New Address of y= 3219901876 New Address of z= 3219901876 New Value of i= 3 New Value of j= 1.500000 New Value of k= c The new address of variable y and z are same. How can two variables have same address and et have different values? Note: I used gcc compiler on Ubuntu 9.04

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  • C++ Array of pointers: delete or delete []?

    - by Jasper
    Cosider the following code: class Foo { Monster* monsters[6]; Foo() { for (int i = 0; i < 6; i++) { monsters[i] = new Monster(); } } virtual ~Foo(); } What is the correct destructor? this: Foo::~Foo() { delete [] monsters; } or this: Foo::~Foo() { for (int i = 0; i < 6; i++) { delete monsters[i]; } } I currently have the uppermost constructor and everything is working okey, but of course I cannot see if it happens to be leaking... Personally, I think the second version is much more logical considering what I am doing. Anyway, what is the "proper" way to do this?

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  • A few questions about char pointers.

    - by m4design
    1- How does this work: char *ptr = "hi"; Now the compiler will put this string in the memory (I'm guessing the stack), and create a pointer to it? Is this is how it works? 2- Also if it is created locally in a function, when the function returns will the memory occupied by the string be freed? 3- Last but not least, why is this not allowed: ptr[0] = 'H'; ?

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  • Pointers in For loops

    - by Bobby
    Quick question: I am a C# guy debugging a C++ app so I am not used to memory management. In the following code: for(int i = 0; i < TlmMsgDB.CMTGetTelemMsgDBCount(); i++) { CMTTelemetryMsgCls* telm = TlmMsgDB.CMTGetTelemetryMsg(i); CMT_SINT32_Tdef id = telm->CMTGetPackingMapID(); ManualScheduleTables.SetManualMsg(i,id); ManualScheduleTables.SetManExec(i,false); } Am I leaking memory every iteration b/c of CMTTelemetryMsgCls* telm = TlmMsgDB.CMTGetTelemetryMsg(i);? The "CMTGetTelemetryMsg(int)" method returns a pointer. Do I have to "delete telm;" at the end of each iteration?

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  • C++: How do I pass a function(without knowing its parameters) to another function?

    - by Ninja
    Hi all. I'm trying to create a function that will store and repeat another function given as a parameter for a specific amount of time or repeats given. But when you want to pass a function as a parameter you have to know all of its parameters before hand. How would I do if I wanted to pass the function as one parameter, and the parameters as another? void AddTimer(float time, int repeats, void (*func), params); // I know params has no type and that (*func) is missing parameters but it is just to show you what I mean Thanks in advance

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  • How to use pointers and pointer aritmetic

    - by booby
    : error C2064: term does not evaluate to a function taking 1 arguments : error C2227: left of '-name' must point to class/struct/union/generic type how do i fix this so this error doesn't happen for(int index = 0; index < (numStudents); index++) { if (student(index + 1)->score >= 90 ) student(index + 1)->grade = 'A'; else if (student(index + 1)->score >= 80 ) student(index + 1)->grade = 'B'; else if (student(index + 1)->score >= 70 ) student(index + 1)->grade = 'C'; else if (student(index + 1)->score >= 60 ) student(index + 1)->grade = 'D'; else student(index + 1)->grade = 'F'; }

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  • Assign pointers in objective C

    - by Tattat
    -(id)setBigObject:(BigObject *)abc{ self.wl = abc; abc.smallObject = self.smallObject; } I have a abc, which is a big Object, when the user pass the bigObject, abc. I assign to my wl value, so , I write "self.wl = abc;", but I want my smallObject assign to the abc's smallObject, so, I do "abc.smallObject = self.smallObject; " So, when I edit the smallObject in self, it will also changed in the abc's also? Am I right?

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  • typedef to store pointers in C

    - by seriouslion
    The Size of pointer depends on the arch of the machine. So sizeof(int*)=sizeof(int) or sizeof(int*)=sizeof(long int) I want to have a custom data type which is either int or long int depending on the size of pointer. I tried to use macro #if, but the condition for macros does not allow sizeof operator. Also when using if-else, typedef is limited to the scope of if. if((sizeof(int)==sizeof(int *)){ typedef int ptrtype; } else{ typedef long int ptrtype; } //ptrtype not avialble here Is there any way to define ptrtype globally?

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