Why sort( ) is taking longer time than qsort( ) in my program?

[V8cTor]

I ran my program using qsort( ) , then again using sort( ).But qsort( ) finished faster than sort( ).why is that?

#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<ctime>
using namespace std;
int compare(const void * a, const void * b)
{
	return (*(int*)a - *(int*)b);
}
void fillRand(int* a, size_t size, int low, int high)
{
	srand(time(NULL));
	int i;
	for (i = 0; i<size; ++i)
	{
		a[i] = rand() % ((high + 1) - low) + low;
	}
}
int main()
{
	size_t size; cout << " size : "; cin >> size;
	int* a = new int[size];
	int l, h; cout << " low : "; cin >> l; cout << " high : "; cin >> h;
	fillRand(a, size, l, h);
	clock_t st, et;
	double diff;
	char answer;
	int option;
	cout << " Which sorting method would you like to apply : \n"
		 << " 1.qsort()\n"
		 << " 2.sort()\n ";
	cin >> option;
	if (option == 1)
	{
		st = clock();
		qsort(a, size, sizeof(int), compare);
		et = clock();
		diff = et - st;
		cout << " time taken = " << diff / CLOCKS_PER_SEC << " sec" << endl;
	}
	else if (option == 2)
	{
		st = clock();
		sort(a, a + size);
		et = clock();
		diff = et - st;
		cout << " time taken = " << diff / CLOCKS_PER_SEC << " sec" << endl;
	}
	else
	{
		cout << " Invalid option\n";
		exit(0);
	}
	delete[] a;
	return 0;
}