I would like to create an array that can store ID and Content in a single cell. I want to store the information so that I could receive both pieces of information from one piece of input.
Currently I am doing it this way:
int order[100];
int content[100];
int count = 0;
//method for adding a new piece of information
void setFrame(int nextOrder, int nextContent){
order[count] = nextOrder;
content[count] = nextContent;
count++;
}
This works, but I would like a way to call a single array, like Array[i], and get two integers from it. How could I accomplish this?
You can use standard class std::pair declared in header <utility>
#include <utility>
//...
std::pair<int, int> order[100];
void setFrame( int nextOrder, int nextContent )
{
order[count++] = { nextOrder, nextContent };
}
Create a struct:
struct Data{
int order;
int content;
};
Data array[100];
int count = 0;
//method for adding a new piece of information
void setFrame(int nextOrder, int nextContent){
array[count].order = nextOrder;
array[count].content = nextContent;
count++;
}
Related
I am looking for some advice on how to organise my C++ code.
I have an int array, side, that I would like to be static in the sense that its value is kept constant between calls. This is because my function foo(), will modify the array side recursively and so I don't want copies to be made of side. Furthermore, the size of side can only be determined at compile time from the size of a vector that is passed into the function bar().
I have thought of the following structure to layout such a problem.
I keep a global int pointer, side, which I can then use to point to the address of my int array and then use the pointer *side within foo to do my modifications.
Please can you give me advise on the layout and organisation of this code? I am quite new to C++ so would appreciate any advice on the below structure.
#include <iostream>
#include <vector>
using namespace std;
int *side;
class A {
public:
int foo(bool);
int bar(vector<int>);
void set_n(int n){ class_n = n;};
private:
int class_n;
};
int A::foo(bool fl)
{
int n = class_n;
for(int i = 0; i < n; i++) {
// modify side[] and then recursively call foo
}
return 0;
}
int A::bar(vector<int> t)
{
int size = t.size();
set_n(size);
int a = foo(true);
int *side_local = new int[size];
for(int i = 0; i < size; i++) {
side_local[i] = 0;
}
side = side_local;
return 0;
}
int main()
{
A a;
vector<int> t = {1, 2, 3};
a.bar(t);
return 0;
}
A recursive call can pass a pointer to itself:
void foo(int *pList)
{
foo(pList); // recursive
}
the same list is then being worked on.
That being said, since foo is inside a class you wouldn't need a global either, but a member variable.
class A
{
int *pMemberList;
...
void foo();
}
now foo can see pMemberList all the time.
BUT ... passing it is probably a better option as in the future your class might house 2 lists that you want to do foo on.
I need some help on multi-dimensional arrays... I cannot find out how to assign a value to an array in a void task, that was created in main.
i tried to find help all over the place, but the longer i keep reading the less i understand
Please help
void addValue(a,b)
{
//somehow assign value to a[2][6] using pointers and such
void main()
{
int dest[7][7] = { 0 };
int a = 2;
int b = 6;
addValue(a,b);
}
Like this:
void addValue( int (*dest)[7], int a, int b )
{
dest[2][6] = 12;
}
int main()
{
int dest[7][7] = { 0 };
addValue(dest, a, b);
}
Consider using std::array instead of C-style arrays; the latter are an anachronism in C++. You can make the 7 a template parameter in addValue if you want to support other dimensions of array.
I've just tried:
class Test
{
public:
int iArray[][];
}
...is this not possible? Do I have to set a constant value?
like:
class Test
{
public:
const int iArray[5][4];
}
I want to define [x][y] later, just have the placements there. Else it wouldn't be "dynamic" and I don't want to use a vector because I want to be able to access the values by "X" and "Y".
I think better way to achieve this is to use pointers. You can do like this.
#include <cstdlib>
#include <iostream>
using namespace std;
class PointerTest {
private:
int** array;
int x, y;
public :
void setValue(int row, int col,int value);
int getValue(int row, int col);
PointerTest(int row, int col);
~PointerTest() {
for(int i=0;i<x;i++) {
delete array[y];
}
}
};
PointerTest::PointerTest(int row, int col) {
x=row, y=col;
for(int i=0;i<row;i++) {
*array=new int[col];
}
}
void PointerTest::setValue(int row, int col, int value) {
*(array[row])=value;
}
int PointerTest::getValue(int row, int col) {
return *(array[row]);
}
int main(int argc, char *argv[])
{
PointerTest* t=new PointerTest(4,5);
t->setValue(0,0,464);
cout<<"The value in array: "<<t->getValue(0,0)<<endl;
system("PAUSE");
return EXIT_SUCCESS;
}
What about
tempalte <int N1, int N2> class Test
{
public:
int iArray[N1][N2];
};
?
What about putting a std::vector in a vector?
std::vector< std::vector< const int > > iArray;
There aren't many reason to use "plain" arrays in C++.
If you want to decide int iArray[][]; size later then you can use vector< vector<int> > iArray;.
The other way is to use nested new[], which would be little complex.
No this is not possible. But you can have a pointer in your class like
int **ptr;
and then in the constructor or where ever allocate the memory for your array with
ptr = (int **)malloc( the size you want );
or with the "new[]"-operator in C++.
but if you are using C++ .. the best way is to use:
std::vector< std::vector< int >> array;
class Test
{
public:
Test()
{
iArray = new int*[5];
for(int i = 0; i < 5; i++)
iArray[i] = new int[4];
}
~Test()
{
for(int i = 0; i < 5; i++)
delete[] iArray[i];
delete[] iArray;
}
int** iArray;
};
Will allow you to allocate a 2d int array at runtime (in this example it is a 5x4), but in all honestly I would use vectors as pointed out by some other posters, you don't need to worry about freeing the memory afterwards like you do with the use of new.
Coming from a Java, PHP background, I am trying to get into C++. I would like to store an array in a struct. My problem is specifying the size of the array after initialising the struct.
Here's my code for the struct:
struct SpriteAnimation {
// ...
int parts; // total number of animation-parts
unsigned int textures[]; // array to store all animation-parts
// ...
};
And here for the main function:
SpriteAnimation bg_anim;
bg_anim.parts = 3;
unsigned int *myarray = new unsigned int[bg_anim.parts];
bg_anim.textures = myarray;
What do I need to change to fix this?
In modern C++, you would use a dynamic container for the inner "array":
struct SpriteAnimation {
std::vector<unsigned int> textures; // array to store all animation-parts
size_t num_parts() const { return textures.size(); }
};
This is by far safer and more modular than anything you could try with manually allocated storage. Usage:
SpriteAnimation x;
x.textures.push_back(12); // add an element
x.textures.push_back(18); // add another element
SpriteAnimation y = x; // make a copy
std::cout << "We have " << x.num_textures() << " textures." std::endl; // report
struct SpriteAnimation {
// ...
int parts; // total number of animation-parts
unsigned int * textures; // array to store all animation-parts
// ...
};
You can use type name[] syntax only if you declare members inline.
Size of a struct must be known at a compilation time.
I worked around the issue through following code.It might be having design issues so please look it up the following code works for me.
#include <iostream>
using namespace std;
struct lol {
// ...
int parts; // total number of animation-parts
unsigned int *texture; // array to store all animation-parts
// ...
};
int main() {
// your code goes here
lol bg_anim;
bg_anim.parts = 3;
unsigned int *myarray = new unsigned int[bg_anim.parts];
bg_anim.texture = myarray;
return 0;
}
Forgive me for using lol instead of your specified name.Do tell me any issues.And help me if there are other issues in my code.
Thank you !! :)
I would like to create a struct and use it inside an other struct as an array. My problem is that I don't know how big array I would like to allocate, I will only know once I am in a function. I mean I would like to use [] instead of a pre-determined constant, like 10000.
I think if you look at my code it would be self-explanatory. Can you help me how to make this code work? Moreover it would help me a lot if you could tell me what is the name of the topic I am asking about (is it dynamic arrays?) and that where can I find articles/tutorials about this topic.
Here is the code with my broken way of thinking about arrays in structs.
#include <iostream>
using namespace std;
struct keyframe {
bool a;
int b;
int c;
};
struct keyframe_file {
const int num_views;
const int num_keyframes;
keyframe keyframes[];
};
int main() {
keyframe_file my_file;
my_file.num_views = 1;
my_file.num_keyframes = 6;
my_file.keyframes = new keyframe[my_file.num_keyframes];
my_file.keyframes[0].a = true;
my_file.keyframes[0].b = 5;
my_file.keyframes[0].c = 9;
return 0;
}
Use a std::vector.
struct keyframe_file {
const int num_views;
const int num_keyframes;
std::vector<keyframe> keyframes;
};
int main() {
keyframe_file frame;
frame.keyframes.resize(...);
}
If it suits your purpose, an STL container (std::vector) is easily one of the best options - the less memory management you have to worry about, the better.
In any case, look at the struct definition Nawaz posted above - that's exactly how it should be. Dynamic arrays in C++ are simply pointers. You have, however, allocated the memory properly in your code, but you haven't freed it (so it's leaking). Since you allocated with new [] you will need to
delete [] my_file.keyframes;
in order to free the memory properly.
Resizing is another issue: with a smart implementation, array resizing can be an amortized O(1) operation which is nice. When you resize, it will always take you O(n) since you need to copy all the elements into a new array of different size, but if you do it half as much, it becomes O(1). That is, double the array each time you need to resize. Here is a very quick example
void resize()
{
if(numOfElementsInArray == sizeOfArray)
{
ArrayType * arr = new ArrayType[sizeOfArray*2]; // Allocate a double size array
for(int i=0;i<sizeOfArray;++i)
currentArray[i] = arr[i];
delete [] currentArray; // Free memory in old array
currentArray = arr; // Set the array to our new one
sizeOfArray *= 2; // Double the size
}
}
NOTE: The example above does not take into account space complexity; that said, if you have 5000 elements, and remove all but 5, this method with not shrink it (which is probably what you will want to do for all practical purposes)
Your code appears to be almost correct, except for two things:
keyframes needs to be a keyframe* rather than a keyframe[]
You forgot to delete the memory you allocated
That is incomplete type. In C++, array must be provided with size, and the size must be known at compile time itself.
You're using new, with which you should be using pointer.
struct keyframe_file {
const int num_views;
const int num_keyframes;
keyframe *keyframes;
};
But std::vector<keyframe> is still a better choice, as #DeadMG already suggested.
By the way, the first two members are const in the struct, that means, they cannot be assigned value, as you're doing in your code. They must be initialized with values you want them to hold. That implies, now with vector, you've to include a constructor, to initialize the struct, as the struct is no more a POD.
struct keyframe_file {
const int num_views; //const member
const int num_keyframes; //const member
std::vector<keyframe> keyframes;
keyframe_file(int nviews, int nkeyframes)
: num_views(nviews), num_keyframes(nkeyframes), keyframes(nkeyframes){}
};
keyframe_file my_file(1,6); //done!
The suggested "Vector" is they safest way to do it.
But if it is only about making your code work (without resizing and stuff) the following should be working:
#include <iostream>
using namespace std;
struct keyframe {
bool a;
int b;
int c;
};
struct keyframe_file {
const int num_views;
const int num_keyframes;
keyframe* keyframes;
};
int main()
{
keyframe_file my_file = {1, 6}; // initialization needed bcause of 'const int'
my_file.keyframes = new keyframe[my_file.num_keyframes];
for (int i = 0; i < my_file.num_keyframes; i++)
{
my_file.keyframes[i].a = true;
my_file.keyframes[i].b = 5 + i;
my_file.keyframes[i].c = 9 - i;
}
return 0;
}
somewhere in your code, when you are done using the array you have to call delete [] my_file.keyframes; as already mentioned.
There's a basic rule when using dynamic arrays in c++, especially when using it inside structs or classes, and it's to delete what you no longer need.
If you want to make your struct dynamic, it's easy, just replace the [] with * and the array will become dynamic, but it's not over yet, there is a lot of work.
You have to construct the array and destory it, and destoroying it is possible and useful noly with destructors, like this:
struct keyframe_file
{
const int num_views;
const int num_keyframes;
keyframe* keyframes;
~keyframe_file() // this is the destructor
{
delete[] keyframes;
}
};
Yet even that code isn't going to work at all, since you are assigning values to constants in variable my_file after creating it, it's illegal in c++, you should then use classes instead.
Using classes with dynamic arrays is very easy and interesting and makes your code very good, you don't have to know too much to do that, just learn what is a constructor, an initializer, destructor, private and public and go on with the following code:
#include <iostream>
using namespace std;
struct keyframe
{
bool a;
int b,c;
};
class keyframe_file
{
public:
keyframe_file(int NV, int NKF):num_keyframes(NKF),num_views(NV)
{
keyframes = new keyframe[num_keyframes];
}
~keyframe_file()
{
delete[] keyframes;
}
private:
const int num_views;
const int num_keyframes;
keyframe* keyframes;
};
int main()
{
keyframe_file my_file(1,6);
return 0;
}
This code works very well, it allows you to assign value to the constants num_views and num_keyframes for one time when creating the object (variable) my_file.
Remember, you are a C++ programmer, be proud of that, and use classes instead of structs and dynamic arrays instead of static ones.
Hope that's useful.
Use pointers and apply to your structure!
int *p;
p = new int;
#include <iostream>
using namespace std;
struct keyframe {
bool a;
int b;
int c;
};
struct keyframe_file {
const int num_views;
const int num_keyframes;
keyframe *keyframes;
};
int main() {
keyframe_file my_file;
my_file.num_views = 1;
my_file.num_keyframes = 6;
for (int i = 0; i < my_file.num_keyframes; i++){
my_file.keyframes = new keyframe; //<---
}
my_file.keyframes[0].a = true;
my_file.keyframes[0].b = 5;
my_file.keyframes[0].c = 9;
return 0;
}