write your own "who"

warning: incompatible implicit declaration of built-in function 'exit'

少了#include <stdlib.h> is by far the best solution.

1)man who
2)info coreutils 'who invocation'
3)man -k utmp
4)man 5 utmp
5)read utmp.h


从文件中读取数据结构
把结构中的信息展示出来
man -k file | grep read
man 2 read
man 2 open
 struct utmp cur_record;
  int utmpfd;
  int reclen = sizeof(cur_record);

  if(( utmpfd = open(UTMP_FILE,O_RDONLY)) == -1) {
    perror( UTMP_FILE );
    exit(1);
  }

  while ( read(utmpfd, &cur_record,reclen) == reclen)
    show_info(&cur_record);
  close(utmpfd);

man -k time | grep transform
man -k time | grep -i convert
/usr/include/time.h
man 3 ctime

你可能感兴趣的:(数据结构)