Arrays/Vectors max elements dimension

[lixo1]

Hi everybody,

I have a curiosity/problem about the dimension of my arrays.
I'm programming under linux & windows & mac, in a mathematical program.
So I need to use arrays and vectors like:

#define N 1000.....
double a[N];
double b[N][N];

But the problem is N. On my Linux I can use N < 1000000 (with g++), on Windows I arrive at N < 10000.
1) I understood that de max. dimension of my array depends of:
a) OS/Hardware limitations with I use a Dynamic Array like:
double *a = new double[N];
b) OS/Hardware + compiler stack size if I use a static array.
Is it correct?

2) Now if I use dynamic arrays, how can I determine (with precision) the maximun dimension (N) of my array that I can allocate, using C++ (or Qt classes)?
NB: My application will get vectors from user, so I would like to determine the OS/Hardware "limit" (before add data) and show a warning.

3) Is there some method/technic in C++ to allocate arrays with "infinite" dimension?

[jsmith]

1) Largely, yes, though global variables are not allocated on the stack; they are elsewhere. The Windows compiler might have an arbitrary limitation on the size of the global data.

2) You can't in a platform independent fashion.

3) No, but you can resize the array to the size you need. Consider looking at
any of the STL containers, particularly vector. vector<> is limited to 2^32
elements or the size of available memory, whichever is tighter.

[lixo1]

Thank you very much for the answers.

[nonzenze]

For such large datasets, a <deque> might be the best option, since it doesn't require contiguous memory. Look it up on the reference section of this site.

[lixo1]

Only a last little thing, someone knows how to calculate exactly the array maximum size (in bits), platform and hardware independent? In differents posts people say things like:
8bits*N, or 32bits*N, or 16bits*N, sizeof(int)*N
Is there a solution?

[helios]

2) You can't in a platform independent fashion.

It depends on the amount of memory available and the size of the elements you want to allocate.
For example, on a system with 2 GB of free RAM and sizeof(int)==4, you can allocate 536,870,912 ints. The number is inversely proportional to the size of the elements, and directly proportional to the amount of free memory.

[lixo1]

Ok, thank you very much for all explanation.