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学会使用fsetpos fgetpos fscanf fprintf等函数的使用
#include <stdio.h>
#include <string.h>
#include <utmp.h>
#include <stdlib.h>
int main(void)
{
FILE *fp,*fp1,*fp2;
struct utmp utmp_buf;
fpos_t pos;
int num=0,cur_num=0;
if( (fp=fopen( "/var/run/utmp","r"))==NULL )
{
perror("error when open the file ! \n");
exit(1);
}
if( (fp1=fopen( "/tmp/utmp_info","w"))==NULL )
{
perror("error when open the file ! \n");
exit(1);
}
while( (fread(&utmp_buf,sizeof(struct utmp),1,fp))>0 )
{
num++;
printf("current_use: %s \n",utmp_buf.ut_user);
fprintf(fp1,"current_use: %s \n",utmp_buf.ut_user);
}
printf("now, read for the last 4 line \n");
fseek(fp,-4*sizeof(struct utmp),SEEK_END);
while( (fread(&utmp_buf,sizeof(struct utmp),1,fp))>0 )
{
printf("current_use: %s \n",utmp_buf.ut_user);
}
printf("now,use fsetpos\fgetpos to read last 4 line \n");
rewind(fp);
while( (fread(&utmp_buf,sizeof(struct utmp),1,fp))>0 )
{
cur_num++;
if( cur_num==(num-4) )
{
fgetpos(fp,&pos);
break;
}
}
fsetpos(fp,&pos);
while( (fread(&utmp_buf,sizeof(struct utmp),1,fp))>0 )
{
printf("current_use: %s \n",utmp_buf.ut_user);
}
fclose(fp);
}
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