Custom Vector Implementation

[Graeme Hart]

So I'm trying to implement a custom vector class and I'm running into compile errors. Also, my code may or may not be totally off. Any help is much appreciated.


MyVector.h

#ifndef __MYVECTOR_H__
#define __MYVECTOR_H__

const int DEFAULT_VECTOR_SIZE = 0;

template<typename T>
class MyVector{
      private:
              int vtr_size;
              T *elements;  // = elements[vtr_size]
              
      public:
             MyVector<T>();
             MyVector<T>(int size);
             //other function prototypes are here
};

#endif;

MyVector.cpp

#include "MyVector.h"


MyVector::MyVector<T>()
{
 vtr_size = 0;
}
                        

MyVector::MyVector<T>(int size)
{                         
 vtr_size = size;
 elements = new T[vtr_size];
 
 while(size >= DEFAULT_VECTOR_SIZE)
 {
  elements = (T*)realloc(elements, vtr_size* sizeof(T));
  size--;
 }

 for(int i=0; i<size; i++)
 {
  elements[vtr_size] = 0;
 }
}

main.cpp

#include <cstdlib>
#include <iostream>
#include <string>
#include "MyVector.h"

using namespace std;

int main(int argc, char *argv[])
{
    
    system("PAUSE");
    return EXIT_SUCCESS;
}

[Dy7SLyTq]

what are the errors?

[Graeme Hart]

Errors are here.

http://imgur.com/NTVqcwk

[Dy7SLyTq]

You have a ; at the end of the endif

[norm b]

MyVector::MyVector<T>()
{
 vtr_size = 0;
}

Your syntax is wrong.

See here: http://www.cplusplus.com/doc/tutorial/templates/
Scroll down to "Class templates"

[cire]

You cannot use realloc with new.

[Graeme Hart]

Made some fixes. Also, I'm not sure I understand why realloc is wrong here, I'm using it with elements, not new T. At the moment I'm getting errors with my function calls in main.cpp

main.cpp

#include <cstdlib>
#include <iostream>
#include <string>
#include "MyVector.h"

using namespace std;

int main(int argc, char *argv[])
{
    MyVector<int>MyVector();

    MyVector<int>MyVector(5);
    
    system("PAUSE");
    return EXIT_SUCCESS;
}

MyVector.h

#ifndef __MYVECTOR_H__
#define __MYVECTOR_H__

const int DEFAULT_VECTOR_SIZE = 0;

template<typename T>
class MyVector{
      private:
              int vtr_size;
              T *elements;
              
      public:
             MyVector();
             MyVector(int size);
             //other function prototypes
};

#endif 

MyVector.cpp

#include "MyVector.h"

template<typename T>
T MyVector<T>::MyVector()
{
 vtr_size = 0;
}
                        
template<typename T>
T MyVector<T>::MyVector(int size)
{                         
 vtr_size = size-1;
 elements = new T[vtr_size];
 
 while(size >= DEFAULT_VECTOR_SIZE)
 {
  elements = (T*)realloc(elements, vtr_size* sizeof(T));
  size--;
 }

 for(int i=0; i<vtr_size; i++)
 {
  elements[vtr_size] = 0;
 }
}

Errors

main.cpp:
12: expected primary expression before "int"
12: expected ';' before "int"

[norm b]

Constructors don't have a return type.

Read the last section "Templates and multiple-file projects":
http://www.cplusplus.com/doc/tutorial/templates/

Then you would instantiate objects like so:

MyVector<int> v1;

MyVector<int> v2(5);

[Graeme Hart]

Got that a few minutes before your comment. now getting a Linker error. Anyways, I think I've got this. thanks a bunch guys.

[Graeme Hart]

Or not.
Getting:

[Linker Error] undefined reference to 'MyVector<int>::MyVector(int)'
ld (Id?) returned 1 exit status
[Build error] error 1

This is running on Dev C++ as a requirement for my class. I understand it's saying I need to implement that function, but it is clearly implemented in MyVector.cpp....

[zb0S216C]

http://www.cplusplus.com/forum/general/101554/#msg545850
http://www.cplusplus.com/forum/beginner/63833/#msg345417 (last post)

_Wazzak

[norm b]

From the link in my last post:

Because templates are compiled when required, this forces a restriction for multi-file projects: the implementation (definition) of a template class or function must be in the same file as its declaration. That means that we cannot separate the interface in a separate header file, and that we must include both interface and implementation in any file that uses the templates.

[Graeme Hart]

Oh wow, thanks so much. I would have never figured that out, didn't even know what to look for. See my reasoned logic is great, but my computer logic is pretty fuzzy still, and I don't known as much as I should to be honest. Thanks for the help!


Is this right because it's still not wanting to work....

#ifndef __MYVECTOR_H__
#define __MYVECTOR_H__

const int DEFAULT_VECTOR_SIZE = 0;

template<typename T>
class MyVector{
      private:
              int vtr_size;
              T *elements;
              
      public:
             MyVector();
             MyVector(int size);
             /*
             void push_back(T element);
             void pop_back();
             unsigned int size();
             T at(int index);
             bool empty();
             void clear();
             void swap(MyVector v2);
             */
};

template<typename T>
MyVector<T>::MyVector(){
 vtr_size = 0;
}
                       
template<typename T>
MyVector<T>::MyVector(int size){                         
 vtr_size = size-1;
 elements = new T[vtr_size];
 
 while(size >= DEFAULT_VECTOR_SIZE)
 {
  elements = (T*)realloc(elements, vtr_size* sizeof(T));
  size--;
 }

 for(int i=0; i<vtr_size; i++)
 {
  elements[vtr_size] = 0;
 }
}
#endif 

[norm b]

What errors do you get?

[Graeme Hart]

Just the Linker error. "Undefined reference" same one.

[norm b]

Compiles fine here. I copied your MyVector.h, added #include <cstdlib> at line 3 and used the following main.cpp:

#include "MyVector.h"

int main(){
    MyVector<int> v1;
    MyVector<int> v2(5);
}

I'm compiling from the command line on a Linux box. I'm not familiar with Dev C++. Do you need to clean your project (run make clean)?

[Graeme Hart]

Oh, that worked. Toldja I'm not very good at this. Well that problem took entirely too long to fix. Thanks again guys.