Redirection of stdin and stdout in a C Program

Question

I am using the typical puts , printf and getchar functions in my Windows console application. Now I would like to redirect the stdout and the stdin to a COM port.

Redirecting stdout alone is working fine:

freopen ("COM1", "w", stdout);

Afterwards all output is going to COM1 as expected.

However with the input I am facing two problems:

freopen ("COM1", "r", stdin);

1) Only stdin redirected, COM1 opens ok. But getchar (or similar functions) do not return characters from COM1. getchar does never return. I tried several modes (r, r+, rb, even w).

2) If stdout is already redirected to COM1, the call to freopen for stdin fails (returns NULL). Likely because COM1 is already in use for stdout.

Environment: Console Application, Windows 7, MinGW

Am I doing something wrong? Is there another (or better) way to accomplish the redirection?

Thanks for any help!

Answer 1

I can't test it right now because I only have a virtual windows machine reachable by RDP, without serial connection, but still, shouldn't something like this work?

int comfd = open("COM1", O_RDWR);
dup2(comfd, 0);
dup2(comfd, 1);

Or, if you dislike hardcoded fds

int comfd = open("COM1", O_RDWR);
dup2(comfd, fileno(stdin));
dup2(comfd, fileno(stdout));