read函数不能读
最近在写一个自己的“who”命令，在使用read函数读文件的时候，遇到问题了，read始终读不到数据！具体的源码如下：基本的原理是这样，who命令实际上是读文件/var/run/utmp（路径为UTMP_FILE）,其中的数据是以struct utmp结构体保存的，程序只要从/var/run/utmp中以该结构体形式读出数据，再显示出来即可，可是，我在读的时候，怎么都读不出来！
#include<stdio.h>
#include<utmp.h>
#include<fcntl.h>
#include<unistd.h>
int main()
{
struct utmp current_record;
int utmpfd;
int reclen = sizeof(current_record);
if(utmpfd = open(UTMP_FILE,O_RDONLY)==-1){
peeor(UTMP_FILE);
return 0;
}
while( read(utmpfd,¤t_record,reclen)==reclen） //就是这里一直读不到数据？？？？？
show_info(¤t_record);
close(utmpfd);
return 0;
}
void show_info(struct utmp * utmpfd)
{
printf(" % -8.8s",utmpfd->ut_name);
printf(" \n");
} if(utmpfd = open(UTMP_FILE,O_RDONLY)==-1){
这句话缺个括号，应该是
if( (utmpfd = open(UTMP_FILE,O_RDONLY) ) ==-1){
你那样写的话，那个utmpfd就总是0，一般正常的fd都是大于3的 谢谢斑竹啊,我试试
READ()读串口的问题
在RECIEVE()函数里始终读不到READ里的数据啊,快疯了,顺便说一下,我采集的串口数据是GPS模块采集回来的信息.各位大哥,拜托了!!!#include <termios.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/signal.h>
#include <pthread.h>
#include <stdlib.h>
#include <errno.h>
#include "gps.h"
#define BAUDRATE B4800
#define COM1 "/dev/ttyS0"
#define COM2 "/dev/ttyS1"
#define ENDMINITERM 27 /* ESC to quit miniterm */
#define FALSE 0
#define TRUE 1
volatile int STOP=FALSE;
volatile int fd;
GPS_INFO gps_info;
int GET_GPS_OK=FALSE;
char GPS_BUF[1024];
/*void child_handler(int s)
{
printf("stop!!!\n");
STOP=TRUE;
}*/
/*--------------------------------------------------------*/
void* show_gps_info(void * data)
{
while(1){
if(GET_GPS_OK){
GET_GPS_OK=FALSE;
printf("%s",GPS_BUF);
gps_parse(GPS_BUF,&gps_info);
show_gps(&gps_info);
}
usleep(100);
if(STOP)break;
}
}
/*--------------------------------------------------------*/
void* receive(void * data)
{
int i=0;
char c;
int ss=0;
char buf[1024];
GPS_INFO GPS;
printf("read modem\n");
while (STOP==FALSE)
{printf("read modem\n");
ss=read(fd,&c,1024); /* com port */
printf("%d/n",ss);
printf("read modem\n");
buf[i++] = c;
if(c == '\n'){
strncpy(GPS_BUF,buf,i);
i=0;
GET_GPS_OK=TRUE;
}
//if(STOP)break;
//write(1,&c,1); /* stdout */
}
printf("exit from reading modem\n");
return NULL;
}
/*--------------------------------------------------------*/
int main(int argc,char** argv)
{ int fd;
fd_set rd;
int i;
if((fd=open_port(fd,1))<0)
{
perror("open_port error");
return;
}
if((i=set_opt(fd,4800,8,'N',1))<0)
{
perror("set_opt error");
return;
}
/*struct termios oldtio,newtio,oldstdtio,newstdtio;
struct sigaction sa;
int ok;
void * retval;
fd = open(COM1, O_RDWR );
if (fd <0) {
perror(COM1);
exit(-1);
}
tcgetattr(0,&oldstdtio);
tcgetattr(fd,&oldtio); // save current modem settings
tcgetattr(fd,&newstdtio); // get working stdtio
newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;//ctrol flag
newtio.c_iflag = IGNPAR; //input flag
newtio.c_oflag = 0; //output flag
newtio.c_lflag = 0;
newtio.c_cc[VMIN]=1;
newtio.c_cc[VTIME]=0;
// now clean the modem line and activate the settings for modem
tcflush(fd, TCIFLUSH);
tcsetattr(fd,TCSANOW,&newtio);//set attrib
*/
while(1)
{
receive(0);
//show_gps_info(0);
//while(!STOP){
//usleep(100000);
//}
}
/*tcsetattr(fd,TCSANOW,&oldtio); // restore old modem setings
tcsetattr(0,TCSANOW,&oldstdtio); // restore old tty setings
close(fd);
exit(0);*/
}
/* 绔彛璁剧疆*/
int set_opt(int fd,int nspeed,int nbits,char nevent,int nstop)
{
struct termios newtio,oldtio;
if(tcgetattr(fd,&oldtio)!=0)
{
perror("setupserial 1");
return (-1);
}
bzero(&newtio,sizeof(newtio));
/*璁剧疆瀛楃澶у皬*/
newtio.c_cflag|=CLOCAL|CREAD;
newtio.c_cflag&=~CSIZE;
/*璁剧疆鏁版嵁浣?/
switch(nbits)
{
case7:
newtio.c_cflag|=CS7;
break;
case8:
newtio.c_cflag|=CS8;
break;
}
/*璁剧疆濂囧伓鏍￠獙浣?/
switch(nevent)
{
case 'O': //濂囨暟
newtio.c_cflag|=PARENB;
newtio.c_cflag|=PARODD;
newtio.c_iflag|=(INPCK|ISTRIP);
break;
case 'E': //鍋舵暟
newtio.c_iflag|=(INPCK|ISTRIP);
newtio.c_cflag|=PARENB;
newtio.c_cflag&=~PARODD;
break;
case 'N': //鏃犲鍋舵牎楠?
newtio.c_cflag&=~PARENB;
break;
}
/*璁剧疆娉㈢壒鐜?/
switch(nspeed)
{
case 2400:
cfsetispeed(&newtio,B2400);
cfsetospeed(&newtio,B2400);
break;
case 4800:
cfsetispeed(&newtio,B4800);
cfsetospeed(&newtio,B4800);
break;
case 9600:
cfsetispeed(&newtio,B9600);
cfsetospeed(&newtio,B9600);
break;
case 19200:
cfsetispeed(&newtio,B19200);
cfsetospeed(&newtio,B19200);
break;
case 115200:
cfsetispeed(&newtio,B115200);
cfsetospeed(&newtio,B115200);
break;
case 57600:
cfsetispeed(&newtio,B57600);
cfsetospeed(&newtio,B57600);
break;
default:
cfsetispeed(&newtio,B19200);
cfsetospeed(&newtio,B19200);
break;
}
/*璁剧疆鍋滄浣?/
if(nstop==1)
newtio.c_cflag&=~CSTOPB;
else if (nstop==2)
newtio.c_cflag|=CSTOPB;
/*璁剧疆绛夊緟鏃堕棿鍜屾渶灏忔帴鏀跺瓧绗?/
newtio.c_cc[VTIME]=0;
newtio.c_cc[VMIN]=0;
/*澶勭悊鏈帴鏀跺瓧绗?/
tcflush(fd,TCIFLUSH);
/*婵
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