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I'm implementing a sequential program for sorting like quicksort. I would like to test the performance of my program in a huge array of 1 or 10 billions of integers. But the problem is that I obtain a segmentation error due to the size of the array.
A sample code of declaration of this array:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define N 1000000000
int main(int argc, char **argv)
{
int list[N], i;
srand(time(NULL));
for(i=0; i<N; i++)
list[i] = rand()%1000;
return 0;
}
I got a proposition to use mmap function. But I don't know how to use it ? can anybody help me to use it ?
I'm working on Ubuntu 10.04 64-bit, gcc version 4.4.3.
Thanks for your replies.
321
Usually you need to create such an array dynamically on the heap. int *integer_array = (int*)malloc(2000000 * sizeof(int)); float *float_array = (float*)malloc(2000000 * sizeof(float)); The array might be too large for stack allocation, e.g. if used not globally, but inside a function.
Since the index of the array is int, the approximate index value can be 2^31 – 1. Based on this approximation, we can say that the array can theoretically hold 2,147,483,647 elements.
You can declare an array without a size specifier for the leftmost dimension in multiples cases: as a global variable with extern class storage (the array is defined elsewhere), as a function parameter: int main(int argc, char *argv[]) . In this case the size specified for the leftmost dimension is ignored anyway.
You can declare one-dimensional (1D) arrays with any non-negative size. int [] arr = new int[ 10 ]; // Array of size 10 int [] arr2 = new int[ 100 ]; // Array of size 100 int [] arr3 = new int[ 1 ]; // Array of size 1 int [] arr4 = new int[ 0 ]; // Array of size 0!
If you have a 32-bit address space and a 4-byte int, then you can't create an array with a billion int s; there just won't be enough contiguous space in memory for that large an object (there probably won't be enough contiguous space for an object a fraction of that size).
Facts about Array in C/C++: Array elements are accessed by using an integer index. Array index starts with 0 and goes till size of array minus 1. Name of the array is also a pointer to the first element of array.
You can declare an array of any data type (i.e. int, float, double, char) in C. The following ways can be used to declare and initialize an array in C. Arrays can be declared by specifying the size or the number of array elements.
This array can hold at most 6 integer elements. A “for loop” is used to input the array elements from the user. Similarly, a “for loop” is used to print these elements in the output.
Michael is right, you can't fit that much on the stack. However, you can make it global (or static) if you don't want to malloc it.
#include <stdlib.h>
#include <time.h>
#define N 1000000000
static int list[N];
int main(int argc, char **argv)
{
size_t i;
srand(time(NULL));
for(i=0; i<N; i++)
list[i] = rand()%1000;
return 0;
}
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