Hi all. I'm new to this list.
The test code at the end of this post has some problem on Cygwin.
What the code does are:
use forkpty() to open pty master (and slave for child),
write a character 'A' to the slave,
duplicate the master file descriptor,
and read() from the (duplicated) master.
If I run this code on either cygwin or cygwin64, I get:
$ ./a.exe
c = A
$ ./a.exe foo # any argument is OK. just to make argc>1
read: Bad file descriptor
If no arg is given (argc=1) then the read() succeeds, while
if argc>1, in which case **the original master is closed**,
then read() fails with "Bad file descriptor".
Am I doing something stupid?
The code runs normally (read() never fails) on Linux and Mac OS X.
I tried dup2() or fcntl(oldfd,F_DUPFD) to no avail. Also tried
open("/dev/ptmx") to open the master but it didn't work either.
#include <stdio.h>
#ifdef __APPLE__
#include <util.h>
#else
#include <pty.h>
#endif
#include <stdlib.h>
#include <unistd.h>
int main(int argc, char* argv[])
{
int fd;
pid_t pid = forkpty(&fd, 0, 0, 0);
if(pid < 0) {
perror("forkpty");
return 1;
}
else if(pid==0) { /* child */
close(fd);
write(1, "A", 1);
exit(0);
}
else { /* parent */
char c;
int oldfd = fd;
fd = dup(oldfd);
if(fd < 0) {
perror("dup");
return 2;
}
if(argc > 1)
close(oldfd); /* this causes a trouble */
if(read(fd, &c, 1) == 1)
fprintf(stderr, "c = %c\n", c);
else
perror("read");
close(fd);
return 0;
}
}
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