请教下g++编译问题

#include <iostream>

using namespace std;

struct link{
int data;
link * next;
};

void createlink(link * head)
{
int num = 0;
int loop = 0;
link * p = NULL;
link * q = NULL;

cout << "请输入链表节点的个数：";
cin >> num;

p = head;

cout << "请输入表中节点的元素：" << endl;
for (; loop < num; loop++)
{
q = new link;
cin >> q->data;
p-> next = q;
p = q;
}
p->next = NULL;
}
void showlink(link * head)
{
link * p = NULL;

cout << "得到如下的单链表：" << endl;
for (p = head->next; p != NULL; p = p->next)
{
cout << p->data << "->";
}
cout << "NULL" << endl;
}

int main()
{
link * head = NULL;

head = new link;
head->next = NULL;

createlink(head);
showlink(head);

return 0;
}

在vc下编译没有错误。用g++编译

t1.cpp:12:17: error: variable or field ‘createlink’ declared void
test1.cpp:12:24: error: ‘head’ was not declared in this scope
为什么？？