Thread: allocation on heap, scalar/non scalar types

>When allocating memory using new on the heap (or free store) you must use a pointer correct.
No, but if you want to keep a reference to that memory you do.

>When attempting to allocate to a basic type like a string variable I get an error about conversion to non-scalar type.
Are you trying to assign the result of new to a non-pointer type? If so, that won't work, new gives you a pointer, and assigning an address to a non-pointer type is likely not a good idea.

well thats just plain stupid.....
try this...

string* ptr = new string("foo");

remember new returns a pointer.

Reread Prelude´s post again, especially the second quote and you will understand that it should be

Code:

//I wouldn´t define a string object this way unless it´s REALLY necessary 
string *word = new string("foo");

also don´t forget to deallocate memory with delete.

Maybe I misunderstood the first part of the post.
She said that it is not necessary to use a pointer, which is what I was failing to do in.
string word = new string("foo");

I understand that new returns a pointer and hence
string * word = new string("foo");
works

but this is what confused me in the reply

>When allocating memory using new on the heap (or free store) you must use a pointer correct.
No, but if you want to keep a reference to that memory you do.

I think what she thought I meant was somthing like this
string * ptrword = new string("foo");
string word=*ptrword;

not sure though.

ok I get she said that assigning to a non pointer type using new is simply assigning the address hence it would have had to been type double or somthing hence my error and misunderstanding and the fact that it is possible but probably not what was intended.

Thanks for the replies
string is non-scalar ie not a number and there fore can't accept an address. So now I understand the real meaning behind the error I think.

>She said that it is not necessary to use a pointer
It isn't. The following is perfectly legal:

Code:

#include <string>

int main()
{
  new std::string();
}

You'll notice that not one pointer was used in that little program (explicitly at least). However, the above is really dumb. Why would you allocate anonymous memory from the heap and then discard your only reference to it? So technically you don't need a pointer to hold anonymous memory, but not using one makes non sense at all. That was what I meant.

A memory leak! The horror!

Code:

#include <string>

int main()
{
  delete new std::string();
}

Okay, so the program returns right away... It's still leaky, I say!

Bottom line is that new and malloc return the address of a chunk of memory. Whether you keep track of it is another issue altogether. If you're just needing a single object from the heap, you could use a reference like this:

int & i = *new int;
delete [] &i;

You would use plain delete here, not delete[].