1、获取文件的flags，即open函数的第二个参数:
flags = fcntl(fd,F_GETFL,0);
2、设置文件的flags:
fcntl(fd,F_SETFL,flags);
3、增加文件的某个flags，比如文件是阻塞的，想设置成非阻塞:
flags = fcntl(fd,F_GETFL,0);
flags |= O_NONBLOCK;
fcntl(fd,F_SETFL,flags);
4、取消文件的某个flags，比如文件是非阻塞的，想设置成为阻塞:
flags = fcntl(fd,F_GETFL,0);
flags &= ~O_NONBLOCK;
fcntl(fd,F_SETFL,flags);
获取和设置文件flags举例::
#include
#include
#include
#include
#include
char buf[500000];
int main(int argc,char *argv[])
{
int ntowrite,nwrite;
const char *ptr ;
int flags;
ntowrite = read(STDIN_FILENO,buf,sizeof(buf));
if(ntowrite <0)
{
perror("read STDIN_FILENO fail:");
exit(1);
}
fprintf(stderr,"read %d bytes\n",ntowrite);
if((flags = fcntl(STDOUT_FILENO,F_GETFL,0))==-1)
{
perror("fcntl F_GETFL fail:");
exit(1);
}
flags |= O_NONBLOCK;
if(fcntl(STDOUT_FILENO,F_SETFL,flags)==-1)
{
perror("fcntl F_SETFL fail:");
exit(1);
}
ptr = buf;
while(ntowrite > 0)
{
nwrite = write(STDOUT_FILENO,ptr,ntowrite);
if(nwrite == -1)
{
perror("write file fail:");
}
if(nwrite > 0)
{
ptr += nwrite;
ntowrite -= nwrite;
}
}
flags &= ~O_NONBLOCK;
if(fcntl(STDOUT_FILENO,F_SETFL,flags)==-1)
{
perror("fcntl F_SETFL fail2:");
}
return 0;
}