Concurrent Input and Output in Perl
c, perl, pipe
Solution
I think the problem is mostly on the C end rather than the Perl end. C sees that its standard-output is going to a pipe, so it isn't very punctilious about making sure it flushes its standard-output buffer before querying standard-input.
To fix this, you should be able to just add this line:
fflush(stdout);
after the first `printf` and before the `fgets`.
(Disclaimer: Not tested.)
Problem
Recently I've taken up learning pipes for fun. I've gotten stuck on a few parts but I have it mostly figured out I think, however I cannot figure out how to get input to forward to a program and output from that program at the same time. Currently I have this Perl script that handles the piping: ``` #!/usr/bin/perl use strict; use warnings; use threads; use FileHandle; use IPC::Open2; my $cv_program = "./test"; #test is the compiled C program below my $cv_message = ""; my $cv_currentkey = ""; my $pid = open2(*PIN, *POUT, $cv_program); my $thread_pipeout = threads->create('PIPEOUT', \&PIN); $thread_pipeout->detach(); while($cv_currentkey ne "\n") { $cv_currentkey = getc(STDIN); $cv_message .= $cv_currentkey; } print POUT $cv_message; sub PIPEOUT { my $PIN = shift; while(<PIN>) { print $_; } } ``` And then I have this C program which just outputs something, asks for a string, then prints that string: ``` #include <stdio.h> int main(int argc, char const *argv[]) { char input[100] = {0}; printf("This is a test.\n"); fgets(input, 100, stdin); printf("You entered %s\n", input); return 0; } ``` The output from running the Perl script is: ``` ~/Programming/Perl Pipes$ ./pipe.pl Hello This is a test. You entered Hello ``` Notice it blocks while taking input and then prints everything in a block after. I need it to print This is a test, then wait for input like the actual program would. Also I'll note is the reason I use getc instead of STDIN in the Perl script is because I couldn't find a way to get STDIN to not block the output from test.c, however getc isn't working too well at the moment either.