How can I tell if a C struct has a member in Perl XS?

Question

Is there an ExtUtils::* or Module::Build (or other) analog to Ruby's mkmf.have_struct_member?

I'd like to do something like (in the manner of a hints/ file):

....
if struct_has_member("msghdr", "msg_accrights") {
    $self->{CCFLAGS} = join(' ', $self->{CCFLAGS}, "-DTRY_ACCRIGHTS_NOT_CMSG");    
}
...

Config.pm doesn't track the specific information I'm looking for, and ExtUtils::FindFunctions didn't seem quite appropriate here...

Answer 1

I know this is not built into either MakeMaker or Module::Build. There might be a thing on CPAN to do it, but the usual way is to use ExtUtils::CBuilder to compile up a little test program and see if it runs.

use ExtUtils::CBuilder;

open my $fh, ">", "try.c" or die $!;
print $fh <<'END';
#include <time.h>

int main(void) {
    struct tm *test;
    long foo = test->tm_gmtoff;

    return 0;
}
END

close $fh;

$has{"tm.tm_gmtoff"} = 1 if
    eval { ExtUtils::CBuilder->new->compile(source => "try.c"); 1 };

Probably want to do that in a temp file and clean up after it, etc...

Answer 2

I wrote a wrapper around ExtUtils::CBuilder for doing "does this C code compile?" type tests in Build.PL or Makefile.PL scripts, called ExtUtils::CChecker.

For example, you can easily test the above by:

use Module::Build;
use ExtUtils::CChecker;

my $cc = ExtUtils::CChecker->new;

$cc->try_compile_run(
    define => "TRY_ACCRIGHTS_NOT_CMSG",
    source => <<'EOF' );
      #include <sys/types.h>
      #include <sys/socket.h>
      int main(void) {
        struct msghdr cmsg;
        cmsg.msg_accrights = 0;
        return 0;
      }
EOF

$cc->new_module_build(
    configure_requires => { 'ExtUtils::CChecker' => 0 },
    ...
)->create_build_script;