How to create our own dynamic array class in c-CodePudding

I was trying yo create my own array class (similar to std::vector) just for fun but there is some problem... The Array class code itself works and compiles successfully but throws an error if i try to instantiate an object of Array class.

#include<iostream>

template<typename type, int size>
class Array
{
 private:
 type _mArray[size] = new type[size];
 public:
 int Access(int index)
 {
  return _mArray[index];
 }
 int Len()
 {
   return size;
 }
 void Insert(int index, type val)
 {
  _mArray[index] = val;
 }
 ~Array()
 {
  delete[] _mArray; 
 }
};//All code above compiles successfully

int main()
{
  Array<int, 2> name; //this line throws an error
}

I am a bit new to C so if someone can explain then I will be very thankful....

Btw here is the error Array initializer must be an initializer list

CodePudding user response：

type _mArray[size] = new type[size];

The template instantiates with: type is int, and size is 2. Therefore, this becomes:

int _mArray[2] = new int[2];

This obviously does not make much sense. If you put this, verbatim, in your main() your C compiler will also serve you with the same complaint.

It's clear that the intent here is, simply:

type _mArray[size];

And nothing else.

P.S. Now, let's go back and reread what the suffering C compiler was struggling to communicate here:

Array initializer must be an initializer list

int _mArray[2] is, obviously, an array. There's an = stuck after it. Ok, this must be array initialization. How do you initialize an array in C ? With a braced initialization list, of course. This would be something like this, for example:

int _mArray[2]={1, 2};

The C compiler saw nothing of that kind, and was trying to tell you that.

CodePudding user response：

#include<iostream>

template<typename type, int size>
class Array
{
 private:
 type * _mArray ;
 public:
 int Access(int index)
 {
  return _mArray[index];
 }
 int Len()
 {
   return size;
 }

 Array()
 {
   _mArray = new type[size];
 }
 ~Array()
 {
  delete[] _mArray; 
 }
 int& operator[](int index){
    return _mArray[index];
 }
};//All code above compiles successfully

int main()
{
  Array<int, 2> name; 
  name[0] = 1024;
  name[1] = 100;

  for(int i= 0; i< name.Len(); i  )
  {
     std::cout<< name[i] << std::endl;
  }

}

CodePudding user response：

You can get it to build using the following minimal change:

@@ -4,7  4,7 @@ template<typename type, int size>
 class Array
 {
  private:
- type _mArray[size] = new type[size];
  type* _mArray;
  public:
  int Access(int index)
  {
@@ -18,6  18,10 @@ class Array
  {
   _mArray[index] = val;
  }
  Array()
  {
   _mArray = new type[size]; 
  }
  ~Array()
  {
   delete[] _mArray;

Basically, you should be initializing the array in your constructor, and store a pointer to it as a class member. The following code builds:

#include<iostream>

template<typename type, int size>
class Array
{
 private:
 type* _mArray;
 public:
 int Access(int index)
 {
  return _mArray[index];
 }
 int Len()
 {
   return size;
 }
 void Insert(int index, type val)
 {
  _mArray[index] = val;
 }
 Array()
 {
  _mArray = new type[size]; 
 }
 ~Array()
 {
  delete[] _mArray; 
 }
};//All code above compiles successfully

int main()
{
  Array<int, 2> name; //this line throws an error
}