Comparing merge sort implementations for doubly linked lists

list_sort.c

/* Compiling: Create a file named list_sort.c in the src/ folder and
 * run:
 * 
 * gcc list_sort.c lcthw/list.o lcthw/list_algos.o -I . -O2
 *
 * Time: 14.025s
 * 
 */
#include "lcthw/list.h"
#include "lcthw/list_algos.h"

int
int_cmp(void *lhs, void *rhs) {
    return (int)lhs - (int)rhs;
}

int
main() {
    List *l = List_create();
    int i;
    for (i = 0; i < 5000000; ++i) {
        List_push(l, (void*)i);
    }
    List_merge_sort(l, int_cmp);
    return 0;
}

list_sort.cpp

/* Compiling: Create a file named list_sort.cpp in the src/ folder and
 * run:
 * 
 * g++ list_sort.cpp -o a.out.cpp -O2
 *
 * Time: 0.647s
 *
 */
#include <list>
#include <iostream>

using namespace std;

int
main() {
    list<int> *pl = new list<int>;
    list<int> &l = *pl;
    int i;
    for (i = 0; i < 5000000; ++i) {
        l.push_back(i);
    }
    l.sort();

    // Add cout to prevent compiler from optimizing everything out.
    cout<<"smallest element: "<<l.front()<<endl;
    return 0;
}