使用 poll 从管道读取
我试图使用轮询从管道读取数据，这里是代码：
#include <stdio.h>
#include <fcntl.h>
#include <poll.h>
#define MAX_BUFF_SIZE 128
int main(void){
char buff[MAX_BUFF_SIZE];
char *buf;
int fd,ret,len;
struct pollfd fdinfo[1];
if((fd = open("/home/s/pipe", O_RDONLY)) == NULL) {
printf("Error Opening File.\n");
exit(1);
}
fdinfo[0].fd = fd;
fdinfo[0].events = POLLIN|POLLPRI ;
while(1){
ret = poll(fdinfo,1,-1);
if (ret < 0) printf("\n\r error");
if ( ((fdinfo[0].revents&POLLIN) == POLLIN) || ((fdinfo[0].revents&POLLPRI) == POLLPRI) ){
len = read(fdinfo[0].fd, buff, MAX_BUFF_SIZE);
if (len > 0){
buff[len] = 0;
buf = (char *) malloc(len);
memcpy(buf, buff, len);
printf("\n read len %d\n %s",len, buf);
free(buf);
}
}
}
return 0;
}
它似乎工作不正常 - 在每个正确的数据之后，我在输出中得到很多垃圾，但我不知道它来自哪里。所以我寻求帮助。
提前谢谢
im trying to read data from pipe using poll, here is code:
#include <stdio.h>
#include <fcntl.h>
#include <poll.h>
#define MAX_BUFF_SIZE 128
int main(void){
char buff[MAX_BUFF_SIZE];
char *buf;
int fd,ret,len;
struct pollfd fdinfo[1];
if((fd = open("/home/s/pipe", O_RDONLY)) == NULL) {
printf("Error Opening File.\n");
exit(1);
}
fdinfo[0].fd = fd;
fdinfo[0].events = POLLIN|POLLPRI ;
while(1){
ret = poll(fdinfo,1,-1);
if (ret < 0) printf("\n\r error");
if ( ((fdinfo[0].revents&POLLIN) == POLLIN) || ((fdinfo[0].revents&POLLPRI) == POLLPRI) ){
len = read(fdinfo[0].fd, buff, MAX_BUFF_SIZE);
if (len > 0){
buff[len] = 0;
buf = (char *) malloc(len);
memcpy(buf, buff, len);
printf("\n read len %d\n %s",len, buf);
free(buf);
}
}
}
return 0;
}
It does not seems to work fine - after each properly data i got a lot of garbage in output, but i dont know where it comes frome. So im asking for help.
thx in advance
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如果至少有
MAX_BUFF_SIZE字节可用，则len将设置为MAX_BUFF_SIZE，并且buff[len]将写入超过buff末尾的内容。在那之后，所有的赌注都消失了。您可以通过将MAX_BUFF_SIZE - 1传递给read()来修复此问题。然而，更令人担忧的是，您没有在
memcpy()调用中复制\0，因为字节数包括>\0是len + 1。当我们这样做时：
malloc( )malloc()的返回值是否为NULLpoll()错误，您仍在检查 < code>revents 字段，该字段将不再适用于if ( ((fdinfo[0].revents&POLLIN) == POLLIN) || ((fdinfo[0].revents& POLLPRI) == POLLPRI) )最好写成if (fdinfo[0].revents & (POLLIN | POLLPRI))但无论如何都没有必要，因为你已经要求 poll() 只查找这两件事If there is at least
MAX_BUFF_SIZEbytes available,lenwill be set toMAX_BUFF_SIZE, andbuff[len]will write past the end ofbuff. After that, all bets are off. You can fix this by passingMAX_BUFF_SIZE - 1toread().However, more worryingly, you're not copying the
\0in yourmemcpy()call, as the number of bytes including the\0islen + 1.While we're at it:
malloc()malloc()isn'tNULLpoll()errors, you're still checking thereventsfield, which won't be applicable any moreif ( ((fdinfo[0].revents&POLLIN) == POLLIN) || ((fdinfo[0].revents&POLLPRI) == POLLPRI) )could better be writtenif (fdinfo[0].revents & (POLLIN | POLLPRI))but shouldn't be necessary anyway, as you've askedpoll()to look for these two things only