creating an array of an object on the freestore in c++ ??

[sde]

i have a class named Album. I would like to create an array the size of 5 on the freestore.

PHP Code:

Album* data[5] = new Album; 


i get the following error in my vc++6 compiler

cannot convert from 'class Album *' to 'class Album *[5]'
There are no conversions to array types, although there are conversions to references or pointers to arrays
Error executing cl.exe.

can anyone help me?

[sde]

well it seems like it didn't like me creating new objects on the same line that i was defining the array.. this seems to work:

int main()
{
int const CAPACITY=5;
Album* data[CAPACITY];


for(int count=0;count<CAPACITY;count++)
{
data[count]= new Album;
data[count]= 0;
}



return 0;
}

[redhead]

And yet, still theres something wrong with it..
you are creating an Album** with the Album* album[5];, if you wan't a static one, where you know it's gonna be 5, then use Album album[5];
Or if you wan't it to be a dynamicaly growing array, then use something like this:

int maxAlbums = 10;
int numAlbums = 0;
Album* albums;

albums = (Album*) malloc(maxAlbums * sizeof(Album));
if(!albums)
  {
    fprintf(stderr, "Not enough heap space\n");
    exit(-1);
  }
while (some_condition)
{
  if(numAlbums >= maxAlbums)
    {
       maxAlbums += 10;
       albums = (Album*)realloc(albums, maxAlbums*sizeof(Album));
        if(!albums)
          {
           fprintf(stderr,"Not enough heap space\n");
           exit(-1);
          }
      }
  albums[numAlbums++] = new Album;
}

Altho this is C, and not C++. I would guess using some kind of vector to store it in, would be the right thing to do. And then just use push and pop to extend it.

[sde]

thanks redhead, .. i haven't done much with it since i got the last thing to work , but i'm going to see what i can do now.

i appreciate it

[sdeming]

Kinda late in the game here, but I'll reply anyway...

int main()
{
int const CAPACITY=5;
Album* data[CAPACITY];


for(int count=0;count<CAPACITY;count++)
{
data[count]= new Album;
data[count]= 0;
}



return 0;
}

There is a memory leak here. When you say data[count] = 0, the reference to the recently allocated Album is lost forever. However, what Redhead says is absolutely right. If you are using C++ you never have to deal with Arrays in this sense again, consider the following:

#include <vector>
class Album { ; } // <-- implement this
int main() {
int const CAPACITY=5;
std::vector<Album*> albums;

for (int count=0; count<CAPACITY;count++) {
albums.push_back(new Album);
}
}

Now you have 5 freshly allocated Album objects, ready for use. To access albums, treat it just like an array:

album[4]->displaySongList();

(or whatever methods are available).

[sde]

thanks scott!

i thought data[count] = 0 was just assigning a null value to my pointers before i did anything with them.. i have a lot to learn.

i just finished my first c++ class last week, .. it was pretty basic, but i am still a beginner at it too.

what is this vector library? is there a good site i can go to find the most common used libraries, and what functions are built into them?

[sdeming]

std::vector<> is part of the Standard Template Library (STL), which was included in the standardization of C++ as part of the Standard C++ Library. It's free and it's extremely powerful!

There are quite a few container template classes available in STL, and once you get used to using them you'll wonder why you'd ever mess with any other language again. Seriously.

Here are a few good links to some of the best C++ writings out there:

STL
- SGI's STL programmers guide: http://www.sgi.com/tech/stl/
- STLPort is a free port of STL, used commonly for maximum compatibility: http://www.stlport.org/

C++ in general
- C++ Boost, some of the most talented C++ coders in the world: http://www.boost.org/ many of their ideas are being nominated for the next ANSI revision.
- C/C++ User Journal, pay close attention to the C++ Experts Forum: http://www.cuj.com/experts/?topic=experts More specifically, read anything and everything written by Scott Meyers or Herb Sutter.

Usenet
- comp.lang.c++.moderated, read anything and everything written by Andrei Alexandrescu. This guy is reinventing the way a lot of people thing about programming, and meta-programming specifically.

If I think of anything else I'll drop a note.

[sde]

Thanks a lot Scott!

This information should be permanent on this site somewhere. I think i'll include it in the version i'm working on if ya don't mind for c++ resources.