使用信号SIGALRM 为 connect 设置超时

#include"apue.h"
typedef void Sigfunc(int);
//void (*signal(int signo,void (*func)(int)))(int);
static void connect_alarm(int);
int connect_timeout(int sockfd,(SA*)pserveraddr,socklen_t len,int sec)
{
    signal(SIGALRM,connect_alarm);
    int res;
    Sigfunc * sigfunc=alarm(sec); //sigfunc restore old sig function
    if((res=connect(sockfd,pserveraddr,len))<0)
    {
        if(errno==EINTR)
        {
            fprintf(stderr,"time out!
");
            errno=ETIMEOUT;
            close(fd);
            return n;    //-1 connection error;
        }
    }
    else
    {
        alarm(0);
        signal(SIGALRM,sigfunc);    //restore old sigfunction
        return n;    // 0 connection success!
    }

}

static void connect_alarm(int)
{
    return ;
}