《Unix/Linux编程实践教程》笔记(1)

第二章讲了文件操作函数（open,read,write,lseek,close），并且编程实现了系统命令who的部份功能，通过man手册，知道who命令就是通过读取var/run/utmp得到用户登录信息，随后man utmp得到文件中存储的结构体源码，最后实现一个0.1版本的who命令。接下来解决了空白记录和时间显示的问题，实现了一个更加好用的who命令。2.6节实现了cp命令，read一个文件的内容在write到另一个文件。2.7节，用缓冲区减少文件读写的次数来提高文件IO效率。

#include	<stdio.h>
#include	<sys/types.h>
#include	<utmp.h>
#include	<fcntl.h>
#include	<time.h>

//#define	INFOFILE	"/var/run/utmp"
#define	INFOFILE	"/var/log/wtmp"

struct logutmp {
	char ut_name[UT_NAMESIZE];
	char ut_line[UT_LINESIZE];
	time_t logintime;
	time_t logoutime;
};
struct logutmp tmplogutmp[256];
int numuse = 0;
long alltime = 0;

void countalltime(char *ut_namep, struct utmp *utbufp)
{
	if (utbufp == ((struct utmp*) NULL)) //已经读到wtmp的结尾，把正登录用户的登出时间设为当前时间
	{
		for ( int i =0; i < numuse; i++)
		{
			if ( strcmp (tmplogutmp[i].ut_name, "houye") == 0 && tmplogutmp[i].logintime != 0 && tmplogutmp[i].logoutime ==0)
			{
				time(&tmplogutmp[i].logoutime);
				alltime += (long)(tmplogutmp[i].logoutime - tmplogutmp[i].logintime);
			}

		}
		return;
	}
	if ( utbufp->ut_type == USER_PROCESS && strcmp(utbufp->ut_name, ut_namep) == 0) //读到wtmp中的登录记录
	{
		int i;
		for ( i = 0; i < numuse; i++ )
		{
			if ( strcmp ( tmplogutmp[i].ut_line, utbufp->ut_line ) == 0)
			{
				tmplogutmp[i].logintime = utbufp->ut_time;
				tmplogutmp[i].logoutime = 0;
				break;
			}

		}
		if ( i >= numuse ) 
		{
			strcpy ( tmplogutmp[numuse].ut_name, utbufp->ut_name );
			strcpy ( tmplogutmp[numuse].ut_line, utbufp->ut_line );
			tmplogutmp[numuse].logintime = utbufp->ut_time;
			tmplogutmp[numuse].logoutime = 0;
			numuse ++;
		}
	}
	if ( utbufp->ut_type == DEAD_PROCESS ) //读到wtmp中的登出记录 ,ut_name 为空，ut_type 设为
	{
		for ( int i = 0; i < numuse; i++ )
		{
			if ( strcmp ( tmplogutmp[i].ut_line, utbufp->ut_line ) == 0 && tmplogutmp[i].logintime != 0)
			{
				tmplogutmp[i].logoutime = utbufp->ut_time;
				printf ("%s  %d -- %d\n", tmplogutmp[i].ut_name, tmplogutmp[i].logintime, tmplogutmp[i].logoutime );
				alltime += (long)(tmplogutmp[i].logoutime - tmplogutmp[i].logintime);
				tmplogutmp[i].logintime = 0;
				break;
			}
		}

	}
	if ( strcmp(utbufp->ut_name, "reboot" ) == 0 || strcmp(utbufp->ut_name, "shutdown") == 0 ) //读到wtmp中的关机重启记录，将所有记录的登出时间设为关机重启时间
	{
		for (int i = 0; i < numuse; i++)
		{
			if ( tmplogutmp[i].logintime != 0)
			{
				tmplogutmp[i].logoutime = utbufp->ut_time;
				alltime += (long)(tmplogutmp[i].logoutime - tmplogutmp[i].logintime);
				tmplogutmp[i].logintime = 0;

			}
		}
	}
	return ;
}


int main(int ac, char **av)
{
	struct utmp	*utbufp;		/* read info into here */

	if ( utmp_open( INFOFILE ) == -1 )
	{
		        fprintf(stderr,"%s: cannot open %s\n", *av, UTMP_FILE);
				        exit(1);
	}   

	do
	{
				utbufp = utmp_next();
				countalltime( "houye", utbufp );
	}while(utbufp != ((struct utmp*) NULL));

	utmp_close( );
	
	double t=alltime/3600.0;
	printf ("%f hours\n", t);
	return 0;			/* went ok			*/
}