who3.c

本函数是一个类linux库函数

/*utmplib.c - functions to buffer reads from utmp file
  *
  *functions are
  *    utmp_open(filename)  --openfile
  *              returns -1 on error
  *    utmp_next( )            -return pointer to next struct
  *              returns NULL on eof
  *    utmp_close( )        - close file
  *
  *  reads NRECS per read then doles them out from the buffer
  */
 #include<stdio.h>
#include<utmp.h>
#include<sys/types.h>
#include<fcntl.h>

#define   NRECS 16
#define   NULLUT ((struct utmp * )NULL)
#define UTSIZE (sizeof(struct utmp))      //zhi ding mei ci du ru de zi jie shu 

static char    utmpbuf [NRECS * UTSIZE] ;     //storage
static int       num_recs ;   // num stored
static int       cur_rec ;   //next to go
static int       fd_utmp=-1 ; //read from

utmp_open(char * filename)
{
    fd_utmp=open(filename,O_RDONLY);   //open it
    cur_rec=num_recs=0;  // no recs yet
    return fd_utmp;     //report
}

struct utmp * utmp_next( )
{
    struct utmp * recp ;
	if( fd_utmp == -1)    //error
	       return NULLUT ;
	if( cur_rec == num_recs && utmp_reload ( ) == 0)   //any more
	       return NULLUT ;

	                               // get address of next record
	 recp = ( struct utmp * ) & utmpbuf [ cur_rec * UTSIZE ] ;
	 cur_rec  ++ ;
	return recp ;
}

int utmp_reload( )
/*
  * read next bunch of records into buffer
  */
{
    int amt_read;  //read them in
    amt_read=read(fd_utmp,utmpbuf,NRECS * UTSIZE); // how many did we get ? 
    num_recs=amt_read/UTSIZE;
   cur_rec=0;
       return num_recs;
}

utmp_close( )
{
    if(fd_utmp!=-1)        //don't close if not
            close(fd_utmp); //open
}
#include<stdio.h>
#include<sys/types.h>
#include<time.h>
#include<utmp.h>
#include<fcntl.h>

#define SHOWHOST

void showtime(time_t);
void show_info(struct utmp * );
	

int main()
{
	struct utmp  * utbufp; //read info into here
	* utmp_next;  //returns pointer to next
	
	

	if( (utmp_open( UTMP_FILE ))==-1)
	{
		perror(UTMP_FILE);//UTMP_FILE is in utmp.h
		exit(1);
	}

	while((utbufp = utmp_next())!= ((struct utmp * )NULL) )
	show_info(utbufp);
	utmp_close();
	return 0; //went ok
}
/*
* show info()  
* displays contents of the utmp struct 
* in human readable form
* *displays nothing if record has no user name
*/
void show_info(struct utmp * utbufp)
{
	if(utbufp->ut_type!=USER_PROCESS) //users only
	return;

	printf("% -8.8s",utbufp->ut_name); //the logname
	printf(""); // a space
	printf("% -8.8s",utbufp->ut_line); //the tty
	printf(""); // a space
	showtime(utbufp->ut_time); //display time
	//printf("% 101d",utbufp->ut_time);//login time
	//printf(""); // a space
	#ifdef SHOWHOST
	if(utbufp->ut_host[0]!='\0')
	printf("(% s)",utbufp->ut_host); // the host
	#endif
	printf("\n"); // newline
}
void showtime(long timeval)
	/*
         * displays time in a format fit for human consumption
         *uses ctime to build a string then packs parts out of it
         *Note:%12.12s prints s string 12 chars wide and LIMITS
         *it to 12 chars
         */
{
	char  *cp ;// to hold address of time
	cp=ctime(&timeval);//convert time to string
                                // string looks like
                                //Mon Feb 4 00:46:40 EST 1991
                                //0213456789012345.
 	printf("%12.12s",cp + 4);                                
}