Thread: Not enough room to store in arrays

Hey guys,

I'm doing a project where I have to take five very large arrays and sort them.
But, I'm getting stuck here.

Here's the part that's bombing out.

Code:

#include <stdlib.h>
#include <stdio.h>

#define BIG 1000000000

int main()
{
	int    a[BIG][7];
	float  b[BIG];
	float  x[BIG];
	float  y[BIG];
	double c[BIG];

	return 0;
}

This results in

Code:

array_test.cpp: In function `int main()':
array_test.cpp:8: error: size of array `a' is too large
array_test.cpp:12: error: size of array `c' is too large
array_test.cpp:9: error: size of variable `float b[1000000000]' is too large
array_test.cpp:10: error: size of variable `float x[1000000000]' is too large
array_test.cpp:11: error: size of variable `float y[1000000000]' is too large

In my full project, the only error I get is:
segmentation fault

I've compiled using gcc and g++ on Red Hat Fedora 1.

Is there any way for the arrays to accept and store this? Thanks for the help!

Originally Posted by Hammer

Use dynamic memory (new/delete). But even then, that's a pretty large number of elements. Maybe allocate only the ammount you're actually using would be better. Or even better still, use the standard containers to do that for you (eg vector or something like that).

I'm afraid I don't understand what you mean by standard containers.

Anyways, here's my updated snippet using the freestore to store the array in.

Code:

#include <stdlib.h>
#include <stdio.h>

int main()
{

	int BIG = 275000000;
	int *pointer;
	pointer = new int[BIG];

	delete pointer;

	return 0;
}

This works, but it doesn't like anything above 275 million.
A problem arose when trying to put a two dimensional array into the freestore.

I tried something like this:

Code:

#include <stdlib.h>
#include <stdio.h>

int main()
{

	int BIG = 1000000;
	int *pointer;
	pointer = new int[BIG][7];

	delete pointer;

	return 0;
}

and the error message I get is:

Code:

array_test.cpp: In function `int main()':
array_test.cpp:9: error: cannot convert `int (*)[7]' to `int*' in assignment

I tried to make the second line in main:
int **pointer;
...but that resulted in a more confusing error message.

What's the correct syntax to do this? Thanks!

I think when Hammer talks of standard containers, he is talking about the STL. Maybe you can use vectors or sets to fullfill your task. You must not worry about reallocating memory, and sort can be used instead of writing your own algorithm.

>>I'm afraid I don't understand what you mean by standard containers
Classes that manage their own memory and that change their size as required. You have no doubt heard talk of the vector class? That is a standard container.

>>but it doesn't like anything above 275 million
Memory is finite. Assuming that integers on your machine are four bytes in length then you are already pushing the the edges of a gigabyte. Virtual memory helps, but not for long at the rate you are going. A better solution would be to work with small manageable pieces rather than the whole.

>>What's the correct syntax to do this?

Code:

int (*pointer)[7];

>>delete pointer;
This is undefined behavior. When you use new [] to allocate memory you must use delete [] to release it.