I'm trying to write a Interpreted programming language like Python, so i need a List class for storing 'address of' functions and variables. I'm implemented Stack class for implementing List class:
typedef unsigned int UIntegerP; //This type for storing addresses
#define Free 0x0
template <typename T> class Stack{
public:
unsigned long UsedBSize; // You can use that like End Of Stack (EOS)
Stack(void){
this->BSize = 0; this->UsedBSize = 0;
this->Buffer = new T;
}
~Stack(void){
delete this->Buffer;
}
inline void Push(T Variable){
if(this->UsedBSize == this->BSize){
this->BSize++;
} this->Buffer[this->UsedBSize] = Variable; this->UsedBSize++;
}
inline T Pop(bool IsProtected = false){
if(IsProtected){
return this->Buffer[this->UsedBSize];
}else{
this->UsedBSize--; T Element = this->Buffer[this->UsedBSize]; this->Buffer[this->UsedBSize] = Free;
return Element;
}
}
private:
T *Buffer;
unsigned long BSize;
};
And this is the class i want to implement:
class List{
private:
Stack<UIntegerP> *stack = new Stack<UIntegerP>; //A stack for storing variable addresses
public:
~List(void){
delete this->stack;
}
List(Stack<UIntegerP> Elements){
while(Elements.UsedBSize != 0){
this->stack->Push(Elements.Pop());
}
}
List(Stack<UIntegerP> *Elements){
while(Elements->UsedBSize != 0){
this->stack->Push(Elements->Pop());
}
}
UIntegerP Get(unsigned long Size); //Get Address with Index number
UIntegerP Set(unsigned long Size, UIntegerP Address); //Set Address with Index number
};
I will use this List class for implementing Python like dictionaries. UIntegerP type is required for Variable class. How i can implement this two functions?
Assuming your stack exposes only the Push and Pop functions, then you can't efficiently implement list with indexing on top of that.
If you're programming in normal C++ style, then the basic data structure would be a dynamic array or a linked list. You can then build a stack on top of those. But note that indexing in a linked list is going to be slow (linear time complexity).
If you're programming in a functional style, then the basic structure is "list", which is an immutable singly-linked list and it's effectively the same as immutable stack. But again, indexing with that is going to be slow.
Also note that your Stack is implemented incorrectly: you're allocating memory for a single T, but then you assume you can use that for an unlimited number of Ts. You either need to go the linked list route: allocate a new node for each item and connect the nodes with pointers; or you need to go the dynamic array route: allocate an array of a certain size and when it gets too small, reallocate it.
Related
So I recently came across a data structure roughly like this:
template<class T>
struct Node {
size_t m_next;
size_t m_prev;
T m_key;
}
template<class T, size_t N>
struct DS {
Node<T> m_elements[N];
size_t m_head;
size_t m_tail;
}
I simplified a bit, just to keep this brief: I don't do error handling when DS gets too full. Normally N is large enough that this isn't a concern.
One note is T must have some way of representing "no value"; why this is needed can be seen below. (I'll refer to this value as TOMBSTONE below.)
The API for this data structure is roughly the same as for a linked list, but it performs much better because everything fits nicely in the cache.
The actual implementation is different from a linked list in that it doesn't need to allocate any new memory for new nodes. For example, pushing to the back of DS is roughly like this:
void DS::push_back(T t) {
size_t attempt = 0;
size_t i = hash(t, attempt++);
while (true) {
if (m_elements[i] == TOMBSTONE) {
m_elements[m_tail].m_next = i;
m_elements[i] = Node(N, m_tail, t);
m_tail = i;
break;
}
i = hash(t, attempt++);
}
}
where hash(T t, size_t attempt) finds places to try to insert new elements. (This is so there's nice spread, rather than clumping everything at the start.)
I hesitate to call this a linked list because of the vast performance and implementation differences from a normal linked list. I also want to point out that this question is not about when to use what data-structures, or if the above data-structure is good/fast/safe/whatever. This data-structure works quite well for us in the very specific situation we use it in.
Is there any name for this particular implementation/data-structure?
It is linked list. It's mentioned on Wikipedia as "Linked list using arrays of nodes"
It's a double-linked linked list, implemented with a C-style array.
i've got these structures:
typedef struct tStimulus_tc
{
short Key;
struct tStimulus_tc *Next;
}Stimulus_tc;
struct Frame_tc
{
int ID; // Frame ID (0..MAX)
int Count; // Felt Count
short sSize; // Stimulus List Size
Stimulus_tc *sList; // Stimulus List
};
if i want to free a "struct Frame_tc" is this enough?
void freeFrame (Frame_tc *fTemp)
{
free(fTemp);
}
or i need to run throught it's stimulus and free 1 by 1?
what's the proper way to free a variable?
free() takes a previously allocated block and releases it for reuse. It doesn't know nor care about the contents of the buffer.
While you could write a compiler that recursively frees pointers, this isn't a good idea:
static Stimulus_tc stim;
Frame_tc *fTemp = malloc(sizeof *fTemp);
fTemp->sList = &stim;
fTemp->sSize = 1;
free(fTemp); // if this recursively freed pointers, we would free a static object
Only you know how your structure is constructed, therefore you shoud be the one destructing it. In your case that means walking the linked list and freeing each member.
In C++, it's advisable to use higher level mechanisms, like using a std::vector<Stimulus_tc> or std::list<Stimulus_tc>.
In cases where pointer use is inevitable (your case isn't one), consider using smart pointers. And if you absolutely must manage memory the old way, use type-safe new[]/delete[].
In C, if your Stimulus_tc list within the struct Frame_tc wrapper is not a traditional head/tail list (e.g. with the final ->Next = NULL), but with the number of nodes contained in list->sSize, you could do something similar to the following:
/* free all nodes in struct Frame_tc->Stimulus_tc list */
void free_list (struct Frame_tc *list)
{
Stimulus_tc *iter = list->sList; /* pointer to iterate list */
Stimulus_tc *victim = NULL; /* pointer to node to delete */
int n = list->sSize; /* number of nodes to delete */
if (iter == NULL) {
fprintf (stderr,"print_list() warning: empty list.\n");
return;
}
while (n--) { /* free n nodes */
victim = iter;
iter = iter->Next;
free (victim);
}
}
If you set the final Next pointer to NULL, you can eliminate int n = list->sSize; and simply iterate over the list with while (iter) { ...
If there were additional pointer elements within each node that were allocated, you would simply free those values before free (victim);
Look it over and let me know if you have any questions.
I want to create a generic linked list in C/C++ (without using templates of C++).
I have written following simple program and it works fine as of now -
typedef struct node
{
void *data;
node *next;
}node;
int main()
{
node *head = new node();
int *intdata = new int();
double *doubledata = new double();
char *str = "a";
*doubledata = 44.55;
*intdata = 10;
head->data = intdata;
node *node2 = new node();
node2->data = doubledata;
head->next = node2;
node *node3 = new node();
node3->data = str;
node3->next = NULL;
node2->next = node3;
node *temp = head;
if(temp != NULL)
{
cout<<*(int *)(temp->data)<<"\t";
temp = temp->next;
}
if(temp != NULL)
{
cout<<*(double *)(temp->data)<<"\t";
temp = temp->next;
}
if(temp != NULL)
{
cout<<*(char *)(temp->data)<<"\t";
temp = temp->next;
}
return 0;
}
My question is -
I need to know the data type of the data I am printing in the code above.
For example - first node is int so i wrote -
*(int *)(temp->data)
second is double and so on...
Instead, is there any generic way of simply displaying the data without worrying about the data type?
I know you can achieve this with templates, but what if I have to do this in C only ?
Thanks,
Kedar
The whole point of a generic list is that you can store anything in it. But you have to be realistic... You still need to know what you are putting in it. So if you are going to put mixed types in the list, then you should look at using a Variant pattern. That is, a type that provides multiple types. Here's a simple variant:
typedef struct Variant
{
enum VariantType
{
t_string,
t_int,
t_double
} type;
union VariantData
{
char* strVal;
int intVal;
double doubleVal;
} data;
} Variant;
You can then tell yourself "I'm storing pointers to Variants in my void* list. This is how you would do it in C. I assume when you say "C/C++" you mean that you're trying to write C code but are using a C++ compiler. Don't forget that C and C++ are two different languages that have some overlap. Try not to put them together in one word as if they're one language.
In C, the only way to achieve generics is using a void*, as you are already doing. Unfortunately, this means that there is no easy way to retrieve the type of an element of your linked list. You simply need to know them.
The way of interpreting data in memory is completely different for different data type.
Say a 32 bit memory block has some data. It will show different values when you typecast it as int or float as both are stored with different protocols. When saving some data in memory pointed by variable of type void*, it does not know how to interpret the data in its memory block. So you need to typecast it to specify the type in which you want to read the data.
This is a little bit like sticking all the cutlery in a drawer, but instead of putting knifes in one slot, forks in another slot, and spoons in a third slot, and teaspoons in the little slot in the middle, we just stick them all in wherever they happen to land when chucking them in, and then wondering why when you just stick your hand in and pick something up, you can't know what you are going to get.
The WHOLE POINT of C++ is that it allows you to declare templates and classes that "do things with arbitrary content". Since the above code uses new, it won't compile as C. So there's no point in making it hold an non-descriptive pointer (or even storing the data as a pointer in the first place).
template<typename T> struct node
{
T data;
node<T> *next;
node() : next(0) {};
};
Unfortunately, it still gets messier if you want to store a set of data that is different types within the same list. If you want to do that, you will need something in the node itself that indicates what it is you have stored.
I have done that in lists a few times since I started working (and probably a couple of times before I got a job) with computers in 1985. Many more times, I've done some sort of "I'll store arbitrary data" in a something like a std::map, where a name is connected to some "content". Every time I've used this sort of feature, it's because I'm writing something similar to a programming language (e.g. a configuration script, Basic interpreter, LisP interpreter, etc), using it to store "variables" that can have different types (int, double, string) or similar. I have seen similar things in other places, such as OpenGL has some places where the data returned is different types depending on what you ask for, and the internal storage has to "know" what the type is.
But 99% of all linked lists, binary trees, hash-tables, etc, that I have worked on contain one thing and one thing only. Storing "arbitrary" things in a single list is usually not that useful.
The answer below is targeting at C++ and not C. C++ allows for what you want, just not in the way that you want to do it. The way I would implement your problem would be using the built-in functionality of the virtual keyword.
Here's a stand-alone code sample that prints out different values no matter the actual derived type:
#include <iostream>
#include <list>
class Base
{
public:
virtual void Print() = 0;
};
class Derived1 : public Base
{
public:
virtual void Print()
{
std::cout << 1 << std::endl; // Integer
}
};
class Derived2 : public Base
{
public:
virtual void Print()
{
std::cout << 2.345 << std::endl; // Double
}
};
class Derived3 : public Base
{
public:
virtual void Print()
{
std::cout << "String" << std::endl; // String
}
};
int main(void)
{
// Make a "generic list" by storing pointers to a base interface
std::list<Base*> GenericList;
GenericList.push_back(new Derived1());
GenericList.push_back(new Derived2());
GenericList.push_back(new Derived3());
std::list<Base*>::iterator Iter = GenericList.begin();
while(Iter != GenericList.end())
{
(*Iter)->Print();
++Iter;
}
// Don't forget to delete the pointers allocated with new above. Omitted in example
return 0;
}
Also notice that this way you don't need to implement your own linked list. The standard list works just fine here. However, if you still want to use your own list, instead of storing a void *data;, store a Base *data;. Of course, this could be templated, but then you'd just end up with the standard again.
Read up on polymorphism to learn more.
I have this code that in my mind, it recieved an item called Vehicle and it has to store it in an array called Node. This is the code related to this part of the program:
void Table::process(Vehicle v, int cont) {
char a='A'+cont;
putVehicle(a,v);
Node.a_v[cont]=v;
if(cont==0) a_surt=v.rowVehicle();
}
This is how I have the array on the private part of Table.h:
struct Node{
Vehicle a_v;
};
The error I get is:
error: expected primary-expression before '.' token
I have the includes I need, but everytime I type this: Node.a_v It gives me that error.
Any advice?
If you want to use a struct, you need to declare a Node before using it. Also, the struct needs to contain an array (or better, look into vectors for more flexibility).
struct Node {
Vehicle[10] a_v; // 10 is max number of Vehicles in array
};
Node myNode;
myNode.a_v[cont] = v;
Remember that if you want to keep this Node around and put more things in it, it needs to be declared in the right scope. For example, to have your process function add a Vehicle to a Node that exists outside of the function process, you could something like this:
void Table::process(Node n, Vehicle v, int cont) {
char a = 'A'+cont;
putVehicle(a,v);
if (cont < 10) {
n.a_v[cont] = v;
}
if (cont == 0) a_surt = v.rowVehicle();
}
It kind of looks like you're just trying to use an array. In that case you're looking for something like this:
// This would go somewhere in your program. Again, 10 is just an example.
Vehicle vehicleArray[10];
// Send this array to this function
void Table::process(Vehicle[] vArray, Vehicle v, int cont) {
char a = 'A'+cont;
putVehicle(a,v);
if (cont < 10) { // In a real program, don't hard-code array limits.
vArray[cont] = v;
}
if (cont == 0) a_surt = v.rowVehicle();
}
You should use Node object to get access to the a_v variable. This line
Node.a_v[cont]=v;
Is incorrect. You should do something like that:
Node n;
n.a_v[cont]=v;
everytime I type this: Node.a_v It gives me that error.
Node is a type; types define the structure of a objects, but they do not have fields of their own (except the static fields, which belong to all instances at once; they are accessed differently anyway).
In order to use a . or -> operator, you need an instance of a Node, like this:
Node x;
x.a_v = ...
It is not clear in your case from where the Node instances should be coming, though. In order to access them, you would need to either pass them in as parameters, or make them available statically/globally (not recommended).
Okay, so Node is NOT the name of your array. It's the name of a user-defined type that is supposed to contain an array. Your Node, however, does not contain an array. It contains one Vehicle, named a_v. I assume a_v is supposed to represent an Array of Vehicles. Therefore, you need to allocate the array. Something like this:
struct Node {
Vehicle a_v[AMOUNT];
};
If you don't know at compile-time how large you want your arrays to be, then they must be dynamically allocated, like this:
struct Node {
Vehicle* a_v;
Node() {
a_v = new Vehicle[AMOUNT];
}
};
If it's dynamically allocated, then it must also be deallocated:
struct Node {
Vehicle* a_v;
Node() {
a_v = new Vehicle[AMOUNT];
}
~Node() {
delete[] a_v;
}
};
AND if it's dynamically allocated, you need to add provisions for copying or disable copying:
struct Node {
Vehicle* a_v;
Node() {
a_v = new Vehicle[AMOUNT];
}
~Node() {
delete[] a_v;
}
// Disable copies (with C++11 support):
Node(const Node&) = delete;
Node& operator=(const Node&) = delete;
// Disable copies (without C++11 support) by making them private and not defining them.
private:
Node(const Node&);
Node& operator=(const Node&);
};
Then to access one of the Vehicles, you'd need to do so like this:
Node n; // Declare a node, which contains an array of Vehicles
n.a_v[cont] = v; // Copy a Vehicle into the array of Vehicles
Note, however, that if you declare the Node instance in this function, then it is local and it will go out of scope as soon as your function ends. You need to declare the Node instance as a member of your Table if you want it to persist past the function call.
class Table
{
private:
Node n;
};
Lastly, as others have suggested, I'd highly recommend that you read a C++ book to learn C++. My personal recommendation is this book (5th edition, don't buy 6th or 7th - the author of those editions is terrible).
I'm fairly new to C++ and new to pointers as well. I'm currently working on a stack and was trying to reallocate the memory for the stack as the size of the stack reaches the top however, I'm running into issues. I've already done a lot of research both on Google and stack overflow and have found some information helpful but since I'm so new to stacks and C++ I'm still having issues. I was hoping some bright and intelligent people could at least point me in the right direction.
now... Here's my code.
#include <iostream>
#define STACKMAX 20
using namespace std;
template <class T> class StackTemplated {
private:
int top;
T values[STACKMAX];
public:
StackTemplated();
void push(T i);
T pop(void);
bool empty(void);
};
template <class T> StackTemplated<T>::StackTemplated() {
top = -1;
}
template <class T>void StackTemplated<T>::push(T i) {
if (top == STACKMAX - 1) {
// reallocate top of stack. (this is the area I'm having issues)
char * string1;
string1 = (char *)calloc(STACKMAX, sizeof(char));
if (top == STACKMAX - 1) {
cout << "The stack didn't re-allocate.";
exit(1);
}
} else {
top++;
values[top] = i;
}
}
template <class T> T StackTemplated<T>::pop(void) {
if (top < 0) {
printf("%", "Stack underflow!");
exit(1);
} else {
return values[top--];
}
}
template <class T> bool StackTemplated<T>::empty() {
return (top == -1);
}
Here's a list of a few things I noticed:
STACKMAX is a constant. If you're expanding the stack, how will you keep track of how big it currently is?
The values member is a fixed-size array. You won't be able to change the size of it dynamically without changing how this is declared and allocated.
calloc() allocates a new chunk of memory with the number of bytes you specify. You'll need to somehow copy the existing stack into the new memory block, and free the previous one.
You're allocating only STACKMAX bytes in the call to calloc(). You'll probably want to scale this by sizeof T, in case T is not a char.
There will be a lot of details for you to fix up once you address these major points. Good luck.
The problem is that you don't want to reallocate the top of the stack. Rather, you want to allocate a new array of values which is large enough to hold the new values. Also, since you need to reallocate the array, values should be a pointer.
But how about we forget all this. If we're working in c++, let's use what c++ offers us to make our lives easier. After that's done, then try open things up, if you really feel the need.
One of the things I'm referring to is your use of calloc. Using calloc is a bad idea, particularly when using templates. The problem is that since calloc has no type information, it won't do something as basic as calling a constructor. Constructors are very important in OOP, since they guarantee that an object's invariance when it is created. Instead, use the new[] keyword, like
values = new T[STACKMAX];
This allocates an array of T of STACKMAX length. Of course, as Greg points out, you should reconsider the use of STACKMAX, and use a variable instead. Also, values shouldn't be a static array, but should instead have type T*.
Another thing I was referring to is the fact that you are really trying to implement an array which grows dynamically as needed. In c++, we call such a structure a vector. If you use a vector, your entire code reduces to
#include<iostream>
#include<vector>
using namespace std;
template<class T> class StackTemplated {
private:
std::vector<T> vec;
public:
StackTemplated() { } // the constructor is trivial; in fact, you can leave it out if you want
void push(T i);
T pop(void);
bool empty(void);
};
template<class T>
void StackTemplated<T>::push(T i) {
vec.push_back(i);
}
template<class T>
T StackTemplate<T>::pop(void) {
T top = vec.back();
vec.pop_back();
return top;
}
template<class T>
bool StackTemplate<T>::isEmpty(void) {
return vec.size() == 0;
}
That's all. It's a lot less hairy if you can use an existing data structure to implement the new data structure.
Once you get really comfortable with how a vector works (and there's plenty of explanations / documentation on the web), then try implementing the functionality yourself. Bottom line is, implementing a data structure is a lot easier if you know exactly how it's supposed to behave.
I would declare your values like
T* vaules;
Then use new to create it not calloc. You will need to keep track of the top of the stack and size of it. As Greg says when you grow the stack make sure and copy data over and clean up the old one.