Thread: problem in classes and arrays

i have this code:

Code:

Code:

template <typename T> class Array
{
      private:
      T *nArr;
      int aSize;
      
      public:
      Array() { aSize = 0; }
      ~Array() { delete[] nArr; }
      
      T Element(T nVal)
      {
           T *tArr = new T[aSize+1];
           for(int i=0; i<aSize; i++)
                tArr[i] = nArr[i];
           tArr[aSize] = nVal;
           delete[] nArr;
           nArr = tArr;
           aSize++;
      }
      
      void show()
      {
           for(int i=0; i<aSize; i++)
           cout<<"["<<i<<"] "<<nArr[i]<<"\n";
      }
};


void func(Array<char*> *array)
{
     char str[4] = "abc";
     array->Element(str);
     array->show();
}

int main()
{
     Array<char*> arr;
     
     func(&arr);
     arr.show();
     
     getch();
}

as u can see, i'm creating an object (arr) of type Array<char*> and in the "func()" function i'm trying to assign it a new element ("abc").
then i print the whole array, first in func() and then in main().
when i print it in func(), it prints "abc" like it supposed to, but when i print it in main() it doesn't work properly...
what's the problem?

What do you mean by "it doesn't work poperly"? Is your error compile-time or run-time? Are error messages shown and if so, what are they?

Originally Posted by hk_mp5kpdw

The problem is that you are pushing the address of a local variable onto your Array object. Once the function exits, that address is no longer valid. There are different ways you could cope with this. One possibility would be to make str static. The better way would be to use an Array<string> object instead of what you are doing.

Also I suggest adding something else to your constructor:

Code:

 public:
      Array() { aSize = 0; nArr = 0; }

to use the "string" i need to include string.h? coz i never managed to use it...
are there any other solutions? how come i can't get the value of str and copy it to the array element instead of using its address?

#include <string>

It will behoove you greatly to learn how to use the string class. It's very easy to use. Here's one link to get you started with that: http://www.bgsu.edu/departments/comp...cs/string.html
Here's a lecture on them: http://www.cs.drexel.edu/%7Emcs171/W...CurrentSlide=0

i changed char* to string but when i compile it, it crashes

What errors is your compiler giving you?

i don't get any error from my compiler, when i open it, it just crashes

Well, that single change isn't enough to fix your program. hk_mp5kpdw pointed out that you're setting the pointer nArr to point to tArr which goes out of scope at the end of that function. So, you've got to fix that as well.

no that's not that... i'm allocating tArr with 'new' and it ain't removed when the function ends.

Originally Posted by hiya

no that's not that... i'm allocating tArr with 'new' and it ain't removed when the function ends.

Yes and no. You're leaking memory, so in that way, the data pointed to by tArr is still there, eating up system resources. By the pointer tArr, because it is declared within that block of code, dies at the end of that block of code. Gone, finito, out of scope. Any attempt to reference it afterwards is wrong.

what i'm trying to do is to create a function to split a string into array, but i can't get it to work. do u know any function to split a string?

so you're saying that the way i create a dynamic array is wrong? how whould u do it?