关于C++中的gettime()的疑问

loveguohuasai

用下面的代码求所用时间，前面已经用了头文件#include<dos.h>;，不知道为什么gettime（）就是不行，出“undeclared identifier”这样的错误。why？

struct time
{
        unsigned char h;
        unsigned char m;
        unsigned char s;
};   
void main()
{
int h1,m1,s1;
        struct time current_time1;
        gettime(&current_time1);
        h1=int(current_time1.h);
        m1=int(current_time1.m);
        s1=int(current_time1.s);
        cout<<"现在的时间是: "<<endl;
        cout<<h1<<"时"<<m1<<"分"<<s1<<"秒"<<endl;
……
……//一个计算的代码
……
int h2,m2,s2;
struct time current_time2;
        gettime(&current_time2);
        h2=int(current_time2.h);
        m2=int(current_time2.m);
        s2=int(current_time2.s);
        cout<<"现在的时间是: "<<endl;
        cout<<h2<<"时"<<m2<<"分"<<s2<<"秒"<<endl;
        int h=h2-h1,m=m2-m1,s=s2-s1;
        cout<<"所用时间为: "<<h<<"时"<<m<<"分"<<s<<"秒"<<endl;

}