select() 함수를 이용한 터미널 선택 출력

// 헤더파일
#include <string.h>
#include <sys/time.h>
#include <fcntl.h>
#include <errno.h>
 
ssize_t r_read(int, void *, size_t );
ssize_t r_write(int, void *, size_t );
int readwrite(int, int );
int copy2files(int, int, int, int );

// 함수 라이브러리 파일
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <limits.h>  //  PIPE_BUF 정의되어있는 헤더파일
#include <fcntl.h>
 
#define BLKSIZE PIPE_BUF
 
ssize_t r_read(int fd, void *buf, size_t size) {
   ssize_t retval;
 
   while (retval = read(fd, buf, size), retval == -1 && errno == EINTR) ;
   return retval;
}  
 
ssize_t r_write(int fd, void *buf, size_t size) {
   char *bufp;
   size_t bytestowrite;
   ssize_t byteswritten;
   size_t totalbytes;
 
   for (bufp = buf, bytestowrite = size, totalbytes = 0;
        bytestowrite > 0;
        bufp += byteswritten, bytestowrite -= byteswritten) {
      byteswritten = write(fd, bufp, bytestowrite);
      if ((byteswritten) == -1 && (errno != EINTR))
         return -1;
      if (byteswritten == -1)
         byteswritten = 0;
      totalbytes += byteswritten;
   }
   return totalbytes;
}
 
int readwrite(int fromfd, int tofd) {
   char buf[BLKSIZE];
   int bytesread;
 
   if ((bytesread = r_read(fromfd, buf, BLKSIZE)) == -1)
      return -1;
   if (bytesread == 0)
      return 0;
   if (r_write(tofd, buf, bytesread) == -1)
      return -1;
   return bytesread;
}
 
int copy2files(int fromfd1, int tofd1, int fromfd2, int tofd2) {
   int i;
   int bytesread;
   int maxfd;
   int num;
   fd_set readset;  
   int totalbytes = 0;
 
   if ((fromfd1 < 0) || (fromfd1 >= FD_SETSIZE) ||
       (tofd1 < 0) || (tofd1 >= FD_SETSIZE) ||
       (fromfd2 < 0) || (fromfd2 >= FD_SETSIZE) ||
       (tofd2 < 0) || (tofd2 >= FD_SETSIZE))
      return 0;
 
   maxfd = fromfd1;                     // find the biggest fd for select
   if (fromfd2 > maxfd)
      maxfd = fromfd2; 
 
   for ( i=0; i<3; i++ ) { 
      printf("i = %d\n", i);
      FD_ZERO(&readset);
      FD_SET(fromfd1, &readset);
      FD_SET(fromfd2, &readset);
 
      if (((num = select(maxfd+1, &readset, NULL, NULL, NULL)) == -1) &&
         (errno == EINTR)) 
         continue;
      if (num == -1) 
         return totalbytes;
      if (FD_ISSET(fromfd1, &readset)) {
         bytesread = readwrite(fromfd1, tofd1);
         if (bytesread <= 0)
            break;
         totalbytes += bytesread;
      }
      if (FD_ISSET(fromfd2, &readset)) {
         bytesread = readwrite(fromfd2, tofd2);
         if (bytesread <= 0) 
            break;
         totalbytes += bytesread;
      }
   }
   return totalbytes;
}

// 메인 파일  
#include <stdio.h>
#include <sys/select.h>
#include <sys/types.h>
#include "restart.h"
 
int main( void )
{
	int i=1;
	char buf[256];
	char buf2[256];
	fd_set readset;
	//struct timeval t;
 
	int maxfd, bytesread;
	int fd_read1, fd_read2;	
	int fd_write;
 
	fd_read1 = open("/dev/pts/6", O_RDONLY);   // 스트링을 받아들을 첫번째 터미널 디바이스 파일
	fd_read2 = open("/dev/pts/7", O_RDONLY);   // 스트링을 받아들일 두번째 터미널 디바이스 파일
 
	fd_write = open("/dev/pts/5", O_WRONLY);   // 스트링을 출력할 터미널 디바이스 파일 
 
	maxfd = fd_read1;
	if ( maxfd < fd_read2 ) maxfd = fd_read2;
	if ( maxfd < fd_write ) maxfd = fd_write;
	maxfd++;	
 
	//t.tv_sec = 20;
 
	while ( 1 ) {
		FD_ZERO( &readset );
 
		FD_SET( fd_read1, &readset );
		FD_SET( fd_read2, &readset );
 
		i = select( maxfd, &readset, NULL, NULL, NULL );
		printf("[ read descriptor = %d ]\n", i);	
 
		if ( FD_ISSET( fd_read1, &readset ) ) {
			bytesread = r_read( fd_read1, buf, 256 );
			write( fd_write, buf, bytesread );
		}
		else if ( FD_ISSET( fd_read2, &readset ) ) {
			bytesread = r_read( fd_read2, buf, 256 );
			write( fd_write, buf, bytesread );
		}
		else continue;
	}
 
	//copy2files( fd_read1, fd_write1, fd_read2, fd_write2 );
 
	//printf("fd_read1 = %d, fd_read2 = %d\n", fd_read1, fd_read2);
	//printf("fd_write1 = %d, fd_write2 = %d\n", fd_write1, fd_write2);	
	//printf("max = %d", maxfd);
 
	return 0;
}