#include<stdio.h>
#include<utmp.h>
#include<fcntl.h>
#include<unistd.h>

#define SHOWHOST            /* include remote machine on output */

int main()
{
        struct utmp current_record;     /* read info int here */
        int         utmpfd;             /* read from this descriptor */
        int         reclen = sizeof(current_record);

        if(( utmpfd = open(UTMP_FILE, O_RDONLY)) == -1) {
                perror(UTMP_FILE);      /* UTMP_FILE is in utmp.h */
                exit(1);
        }

        while(read(utmpfd, &current_record, reclen) == reclen)
                show_info(&current_record);
        close(utmpfd);
        return 0;                       /* went ok */
}
show_info(struct utmp *utbufp)
{
        if( utbufp->ut_type != USER_PROCESS )
                return;
        printf("% -8.8s", utbufp->ut_name);     /* the logname */
        printf(" ");                            /* a space */
        printf("% -8.8s", utbufp->ut_line);     /* the tty */
        printf(" ");
        showtime(utbufp->ut_time);
    #ifdef SHOWHOST
        printf("( % s)", utbufp->ut_host);      /* the host */
    #endif
        printf("\n");                           /* new line */
}

void showtime( long timeval )
{
        char *cp;
        cp = ctime(&timeval);
        printf("%12.12s",cp+4);
}
代码如上，调试问题如下：

有大神给个回复嘛，系统是ubuntu16.04，gcc编译

utmp.h文件呢？

utmp.h文件

你的意思是字长的问题？

解决了，谢谢