• Inline::C
• perldoc -f qx

my $foo = qx{ ./external };
[download]

perldoc -f qx

Um, the OP was asking about capturing the exit status of a C program, which involves using the "system()" call (perldoc -f system) -- not "qx" (aka the backtick operator), which just captures the program's stdout. Also -- OOPS, sorry. I should have read the docs more carefully myself, to see that qx returns stdout and sets $? -- thanks, I'm glad I finally learned that. Anyway (end of update), the more direct reference for qx is "perldoc perlop" (which is where "perldoc -f qx" tells you to look).

Another reply below points to the usage of "system()", along with the "$?" variable -- though I prefer using a scalar that has a meaningful name, e.g.:

  my $exit_stat = system( "some_shell_command ..." );
  printf "Shell_command exit status was %d\n", $exit_stat/256;
  print "(which means it probably failed)\n" if $exit_stat != 0;
[download]

(closing remark to updates: my old habit of using "system()" to get the exit status, vs. using backticks to get stdout data, was simply a matter of being unaware of the $? variable, which is set in either case.)

I know I can do a printf (or cout) and capture the standard out in the perl script, but is there a way to in-line a C function/program and get the return value?
Sure! You could do an XS interface, or use Inline::C.

The main reason I am asking this is to get the output from the C function gettimeofday so that I can get the time at micro second granularity.
Oh!No need to complicate then: just use Time::HiRes, and it will make gettimeofday available to you as a function.

The return value of main() in a standalone C program is used as an error or status indication code and should not be used for other purposes. Normally programs should return 0. Its range is also limited: 0-255 (?) integer on most (UNIX) systems.

If that's what you really want (I doubt), here's how you can get to it (tested on Linux) (see perldoc perlvar for documentation on $?)

$ cd /tmp
$ cat > ret5.c
int main(int argc, char **argv)
{
  return 5;
}
^D
$ gcc ret5.c -o ret5
$ perl
system './ret5';
printf "child return code is: %d\n", $? >> 8;
^D
child return code is: 5
$
[download]

#!/usr/bin/perl
use warnings;
use strict;
use IPC::Open3;

#interface to "bc" calculator 
#my $pid = open3(\*WRITE, \*READ, \*ERROR,"bc"); 
my $pid = open3(\*WRITE, \*READ,0,"bc");
            #if \*ERROR is false, STDERR is sent to STDOUT  
while(1){
print "Enter expression for bc, i.e. 2 + 2\n";
chomp(my $query = <STDIN>);

#send query to bc 
print WRITE "$query\n";

select(undef,undef,undef,2);

#get the answer from bc 
chomp(my $answer = <READ>);

print "$query = $answer\n";
}

waitpid($pid, 1);
# It is important to waitpid on your child process,   
# otherwise zombies could be created.
[download]