C++ List Insertion Sort

ListInsertionSort.cpp

struct node heada, headb;
link t, u, x, a = &heada, b;

for ( i = 0, t = a; i < N; i++ )
{
    t->next = malloc( sizeof *t ); 
    t = t->next; t->next = NULL;
    t->item = rand() % 1000; 
}
b = &headb; b->next = NULL;

for ( t = a->next; t != NULL; t = u )
{
    u = t->next;

    for ( x = b; x->next != NULL; x = x->next )
        if ( x->next->item > t->item ) break;
    t->next = x->next; x->next = t; 
}