use strict;
use warnings;

use Inline C => 'DATA';

my $pass_param = 42;

my $ret = test_perlcall( $pass_param );
print "And test_perlcall( $pass_param ) returned $ret\n";

sub return_input {
    shift;
}

__DATA__

__C__


int test_perlcall( int input ) {

    int rv;
    int count;

    dSP;  /* Declare and initialize local copy of Perl stack ptr */

    printf( "Called test_perlcall( %i )\n", input );
    
    /* Create a boundary for temps we create. */
    ENTER;
    SAVETMPS;
    
    /* Make mental note of current stack ptr (even if no params) */
    PUSHMARK(SP);
    
    /* Push a mortal param onto the stack. */
    XPUSHs(sv_2mortal(newSViv( input )));
    
    /* Sync the global stack pointer up to our local */
    PUTBACK;
    
    /* Call the Perl function; keep note of 'count' to test it. */
    /* G_SCALAR flag meaning we want a scalar returned. */
    count = call_pv( "return_input", G_SCALAR );
    
    /* Refresh local copy of stack pointer because */
    /* it may have been invalidated by call_pv()   */
    SPAGAIN;
    
    /* We never want the Perl stack to fall into an      */
    /* inconsistent state, so we must verify that we     */
    /* got exactly one RV where we expected exactly one. */
    if( count != 1 ) croak( "Well, THAT failed to work.\n" );
    
    /* Now that we know we got a RV, we can pop it off the stack. */
    rv = POPi;
    
    printf( "C called Perl function, return_input( %i )\n", rv );
    
    PUTBACK;
    
    /* Free our temps, leave the boundary we created earleir */
    FREETMPS;
    LEAVE;
    
    return rv; /* Inline::C handles this typemap automatically. */
}

##</code><code>##

Called test_perlcall( 42 )
C called Perl function, return_input( 42 )
And test_perlcall( 42 ) returned 42