C++ :: GUI Objects Creation / Deletion?
Mar 31, 2013
I have a basic query regarding GUI Objects (Labels, Combo Boxes etc) creation and deletion in a Dialog Box / Window. If I have the following code:
void MyWindow::someFunction() {
Label* myLabel = new Label(this); // how is it different from just "new Label";
//some code using myLabel;
[Code]....
1. Will myLabel (the object, not the pointer) be visible to me in the nextFuntion?
2. Is it necessary to call delete for the objects that I created in someFunction or are they cleaned up automatically by the compiler?
I am using Qt Creater as the IDE.
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Aug 3, 2014
Any simple example of deletion from the end here is the algorithm
1. If n=0 then array is underflow step
2. A (UB) <------- null
UB <---- UB1
3. Stop
Example:
Suppose array
Arr[0]=5 , Arr[1]=8 , Arr[2]=10 , Arr[3]=7
After Deletion
Arr[0]=5 , Arr[1]=8 , Arr[2]=10
How to delete the last element of array?
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Nov 26, 2013
I've been working on my deletion function for Red and Black trees but can't seem to get it to work. From what I can tell, the remove function, instead of deleting the single value that will my prompt by the user, will delete all the values that are in the red and black tree.
Code:
bool RedBlackTree::remove(int x) {
if(!search(x)){
return false;
} else {
Node* z = new Node(x);
rbremove(z);
[Code] ....
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Jan 14, 2015
I have a doubly linked list from which I need to occasionally delete elements (any elements that have a type value different from 0). The function I have seems to work, but looking at it, I think I could probably make the logic cleaner.
The structs in questions are declared here, with irrelevent variabled omitted:
Code:
struct Event {
//...
int type;
//...
struct Event *next;
struct Event *prev;
[code]....
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Mar 4, 2014
I need to create dynamic array or map. for example
CString *a1;
CString *a2;
CString *a3;
it minimized to using for loop.
for (int i=1;i<=3;i++) {
CString s="a"+"itoa(i)"
CString *s;
}
Something like this. its same as map concept.
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Dec 22, 2013
I have a quick question. I need a way to represent orientation in degrees. I made a class which automatically changes negative angles into positive ones (adds 360 until >0) and makes sure they are under 360 (subtracts 360 until <360).
Now I realized I also need a class to represent angular movement, which must be in the range ]-360;360[
I don't think custom types with the unsigned keyword is a thing, but I'm just looking for a better way to do this then making two classes. Or would you just create a class which inherits from angle and overloads a few methods?
Or I could just use floats to represent rotation, because testing if an object does more than 1 turn per second isn't really required.
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Apr 29, 2014
have a piece of code
for (int i = 0; i<5; i++)
{
CMyStackObject sobj;
//
...
}
Does standard guarantees that instances of sobj will be different for different i?
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May 19, 2013
I'va got a segmentation problem with creation of core dump for the following snippet of c code:
Code:
#include
#include
#include
"lezione.h" studente s1, s2; studenti s;
int main()
{ int codice; char* nome; char* cognome; int esami;
printf("Leggi uno studente da tastiera e memorizzalo in una struct
");
lettura_studente(s1, codice, nome, cognome, esami); return 0;
}
[code]....
In conclusion I'va two problems:
1) Program crash;
2) I can't read struct studente within parameter function. What are the problems?
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Jan 24, 2014
I see many time where static data member is used to count creations of objects -
i.e.
1. the static data member is init to 0
2. the static data member is incremented by 1, in the Class' constructor, every time an object is created
However, if you define a global object of a class,
How can you tell that the static data member is initialized BEFORE the constructor of the global object is called? (i.e. before the global object is created).
Because to my understanding, you do not know in advance the order of global objects' creation -
so the Global Object could be created BEFORE the static data member was created and initialized.
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Nov 12, 2014
This has been bothering me for a while now, and I finally put together an example:
#include <iostream>
#include <string>
using namespace::std;
[Code]....
In the code above, the two classes hold pointers to each other, and that's fine but it doesn't seem right since C++ prefers to pass by reference. Yes, it can still do that (see testbox and testball) but even that seems odd to me because still you need to use pointer notation for the enclosed object. Am I the only one who feels this way, and should I just get over it? Or am I missing something that would allow an object to hold a reference?
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Apr 15, 2013
I'm trying to write a function that takes a 32bit address and a data to store at this address.
I'm wanting to take the 32 bit memory address eg 0x12345678 and split it
into 4 x 2 bytes
12, 34, 56, 78
then each of the 4 entries is at most a 256 entry array.eg
FF, FF, FF, FF
So in this example, 0x12 points to 0x34 in the second array, which points to 0x56 in the third array, which finally points to 0x78 in the last array. This last array holds the actual data.
After successfully doing 0x12345678, say I might get a read for 0x1234AABB. So, the first and second pointers already exist, but I then have to create and write to dynamically created arrays.
The arrays need to have all entries set to NULL so that i know whether to follow the pointers to overwrite a previously entered value or create new arrays and pointers.
It all looks good and simple in the pseudo code I've written up but I'm having trouble coding it. I'm currently trying to deal with the first entry case, ie all array elements are NULL, but I'm getting confused with the pointers and creation of new arrays.
void cpu::store(unsigned int mem_add,unsigned int mem_val) {
int first = (mem_address&4278190080)>>24;
int second = (mem_address&16711680)>>16;
int third = (mem_address&65280)>>8;
int fourth= (mem_address&255);
[Code] .....
A1 has been declared as
int* A1[256] ;
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Apr 2, 2013
i am relatively new to c++, and am trying to make it so particles will gravitationally attract to the mouse pointer. i have gotten all the bugs that the compiler found, but there must be another because the program crashes the second i open it. my code could be way off, so just tell me if it is and ill do more research and learning before trying something like this again. here is the code:
#include <SDL/SDL.h>
#include <iostream>
#include <vector>
#include <math.h>
#include <stdio.h>
using namespace std;
float mouseX;
float mouseY;
[Code] .....
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Oct 20, 2014
I've been really busy but managed to get in enough down time to learn somewhat decent info about vectors. Anyways originally my program created a dynamic array of pointers to class objects and I came across a few problems because of this. Apparently an array of pointers is now outta of the question and I will now be switching to a vector of objects instead.
Why I want a list of objects instead of pointers this little comment should clear things up.
tiles[i]->show() dereferences tiles[i] (i.e. accesses whatever it points at) before calling the show() method.
That is undefined behaviour. Once undefined behaviour occurs, there is no recovery, and there is nothing the show() method (or any subsequently called function for that matter) can do to recover (short of invoking their own forms of undefined behaviour - compiler specific hacks, etc).
Even if the show() method initialises the object correctly, it cannot change the pointer tiles[i] which is in a different scope (within main()).
What I'm trying to do is create a vector of already intialized objects so that I can use a conditional statement of every single element to properly layer my games art resources. This should also automatically fix a mild unrelated collision dectection problem too but first thing first layering.
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Nov 10, 2013
here's the problem. I want to delete the objects within a vector, although I'm not sure whether I should clear the vector afterwards. Is it really necessary?
Code:
for (i = 0; i < allSales.size(); i++)
delete allSales[i];
allSales.clear(); //Is this step necessary?
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Aug 25, 2013
well the question is how to compile objects in a subdirectory?
Code:
./bo/%.o : %.c
$(CC) $(CFLAGS) <$
the command abouve will compile my objects but leave them in the same directory. However I want them in a different directory. in ./bo directory. How to achieve that ? I just realize that if i remove ./bo/ from the line it does not work..
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Jun 6, 2013
I am using OpenCV to read and manipulate a set of images, which I need to store in an array to work with them. Here is a snippet of the code:
#define MAX_IMAGES 8
typedef Mat* MatPtr;
int main(int argc, char** argv) {
char imageName[] = "./res/imageX.tiff";
MatPtr datacube[MAX_IMAGES];
[code].....
I have an array of pointers to Mat objects (an OpenCV class used to hold info and data about an image), which I will use to store the images. The function imread reads an image and returns a Mat object loaded with the relevant data about the image.However, this gives me a nice segfault when the assignment takes place. Of course, I can swap it with the following code, but since I'm working with big images (2048x2048 and upwards), it's really inefficient:
for(unsigned int i = 0; i < MAX_IMAGES; i++) {
imageName[11] = 49 + i;
datacube[i] = new Mat(imread(imageName, -1));
}
Is there any way to do this elegantly and without much hassle?Again, excuse my rustiness and anything completely stupid I might have said. It's been a long time since I worked with C++. Managed to circumvent the problem by using a STD vector instead of an array. I'd still like to know the answer to this riddle...
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Oct 12, 2014
class FlashCard {
public:
int a,b;
void PrintCard(void);
int CorrectAnswer(void);
};
void SwapFlashCard(FlashCard &a,FlashCard &b)
[Code]....
Why does Xode warn me that Type'FlashCard'does not provide a subscript operator on line 22,23,29 and 30?
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Jun 25, 2013
I have the following code below. I am getting a memory access violation when accessing cmd->query_string in the loop function. The loop() function is running in another thread. The cmd object appears to be destroyed after calling the send_command function. How do I create an object on the heap and access the query_string.
std::list<my_command_message_que*> my_command_que;
void loop(){
if(my_command_que.size() > 0){
my_command_message_que * cmd = my_command_que.front();
std::cout << cmd->query_string;
[Code] ....
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Jul 24, 2013
I keep getting an undesired value in this code. I've tried several methods, but none are giving me the correct answer. The out put is always zero, when in this case it should be 10!!
Here's the object structure:
template<class T, class _b>
struct quantity {
private: T value;
public:
explicit quantity(T val): value(val) {};
T getValue() { return value; };
[Code] .....
Here's the operation:
int main() {
quantity<int, bool> m(20);
quantity<float, bool> m_f(10);
quantity<double, bool> m_d(NULL);
m_d = m_f;
[Code] .....
Why does it seem that the assignment operator is the harder operator to overload? Maybe it's just my luck, but I seem to always run into issues whenever I work with it. I hardly ever experience errors when overloading any of the other operators.
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May 20, 2013
I have a question regarding how GCC relates a header file and its binary file.
main.c
#include <math.h>
#include <stdio.h>
int main (void){
double x = sqrt (2.0);
printf ("The square root of 2.0 is %f
", x);
return 0;
}
we can compile it by running the line: gcc main.c -lm -o main
My question is: How GCC knows where is the definition of sqrt?
First I was thinking that there was and object file with the name math.o inside libm.a (that is GCC will look for an object file with the same name as the header file), but after running the next line I think my assumption was wrong as there is not such file in libm.a.
nm libm.a | grep math.o
nm: e_acos.o: no symbols
nm: k_cos.o: no symbols
nm: k_sin.o: no symbols
[Code] ....
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Nov 14, 2013
I've started programming my little program called vLibrary (program I want to make for the library in my city) and after I m done with console application I will try to implement wxWidgets.My program will be able to add new users to the system, new books and new librarians.
Now, I m confused what data types to use and how to store objects (newly created users, books etc) to my program so later on they can log in the system etc. Logic of the program is completely clear to me but I m not sure how to make array of objects and store them in memory or in a certain file, how to store password and make some kind of encryption etc.which data structure from STL should I use and how.
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Feb 8, 2014
I'm currently trying to access a variable contained within a base object from another completely different object and I continually get error messages. I'll attempt to put up the important code since it's contained within fairly large classes. From the Base .cpp file. ObjectPosition:
void ObjectPosition::init(float x,float y, float speed, int boundx, int boundy, float hit, int lives, bool live) {
ObjectPosition::x = x;
ObjectPosition::y = y;
ObjectPosition::speed = speed;
ObjectPosition::boundx = boundx;
ObjectPosition::boundy = boundy;
ObjectPosition::hit = hit;
ObjectPosition::lives = lives;
ObjectPosition::live = live;
}
This is the initialization function for the BaseObject. All objects are inheriting these variables which are Protected within the ObjectPosition class.Then they are initialized within the Pig class thus wise:
void Pig::binit(float sx,float sy, ALLEGRO_BITMAP *simage) {
//Sets all ObjectPosition Variables
ObjectPosition::init(800,900,10,80,40,40,10,true);
smaxFrame = 4;
scurFrame = 0;
[code]...
I tried to initialize the boundx through the pig via pinitx but I get errors and I can't access through the pig to the object position to the boundx.
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Dec 30, 2014
How to get this code working
template <typename T>
class Dummy {
// Implementation
};
template <typename T>
class SomeClass
[Code] ......
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Oct 31, 2014
I have two classes, Parent and Child, where Parent contains a vector that is used to store instances of Child. When I create an instance of Parent, three instances of Child are also created in Parent's constructor and stored in the vector. I understand that push_back() creates a shallow copy of each Child instance and that Child's destructor is called each time the loop (inside Parent's constructor) iterates. The problem is that because Child's destructor is called each time the local variable child goes out of scope, the memory previously allocated in Child's constructor is destroyed and when Child's destructor is called again later on in the program to get rid of the copy stored in vector, the program crashes. I can fix this by overriding the default copy function or by storing pointers to objects instead of copies of objects. I don't really need to use vectors in this case since I always have three children in one parent but I'm doing this as a learning exercise and would prefer to use vectors.
#include <iostream>
#include <vector>
class Child {
public:
Child() {
std::cout << "child constructor called" << std::endl;
[Code] .....
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Nov 6, 2013
I my code i have a base struct ...
Then others structs made ...
struct base{};
struct a1 : base {
int a;
int b;
[Code] ....
Now i must deposit all these containers(maybe & of containers) in another vector...
How i can do that? Can i write
vector<vector<base*> > all;
all.push_back(&v1);
all.push_back(&v2);
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Sep 27, 2013
I've created an Array of pointers to objects using:
Person ** A = new person * [arraysize];
When I intend to access a specific person do I have to do this? :
something = A->[i];
and when I want a specific object within my struct do I have to do this? :
something_else = A->[i]->random_int;
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