Question

write three functions in C++: one that declares a large array statically, one that declares the same array on the stack, and one that creates the same array on the heap. Call each of them a number of times (at least 100,000) and output the time required by each. Explain the results.

Answer 1

#include <stdio.h>

#include <time.h>

#include <stdlib.h>

void static_allocation()

{

    static int array[400000]; //static array memory is alloted in program's data segment

}

void allocation_in_stack_memory()

{

    int array1[400000]; // non static array memmory allocation is done on stack, internally it calls alloca() to allocate memory which allocates from stack

}

void allocation_in_heap_memory()

{

    int *array2 = (int *)malloc(400000 * sizeof(int)); // malloc allocates memory from heap memory

}

int main()

{

    struct timespec time_1, time_2;

    int i;

    //for static allocation

    clock_gettime(CLOCK_REALTIME, &time_1);

    for (i = 0; i < 100000; i++)

        static_allocation();

    clock_gettime(CLOCK_REALTIME, &time_2);

    printf("To do 100000 times static allocation of array size 400000, it took %d nanoseconds\n", time_2.tv_nsec - time_1.tv_nsec);

    //for allocation on stack memory

    clock_gettime(CLOCK_REALTIME, &time_1);

    for (i = 0; i < 100000; i++)

        allocation_in_stack_memory();

    clock_gettime(CLOCK_REALTIME, &time_2);

    printf("To do 100000 times allocation of array size 400000 on the stack memory, it took %d nanoseconds\n", time_2.tv_nsec - time_1.tv_nsec);

    //for allocaion from heap memory

    clock_gettime(CLOCK_REALTIME, &time_1);

    for (i = 0; i < 100000; i++)

        allocation_in_heap_memory();

    clock_gettime(CLOCK_REALTIME, &time_2);

    printf("To do 100000 times allocation of array size 400000 from heap memory, it took %d nanoseconds\n", difftime(time_2.tv_sec, time_1.tv_sec));

    return 0;

}

SAMPLE OUTPUT:

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