Long floating-point number with extern "C"

Sample COBOL usage C++ function

IDENTIFICATION DIVISION.
PROGRAM-ID. COBRTN.
ENVIRONMENT DIVISION.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 X COMP-2.
01 Y COMP-2.
PROCEDURE DIVISION.
     MOVE 3.14159265 TO X.
* X BY VALUE ***
     CALL "CENTRY" USING BY VALUE X
       RETURNING Y.
     GOBACK.
END PROGRAM COBRTN.

#include <stdio.h>
extern "C" {double CENTRY
     (double x);}

double CENTRY(double x)
{
  double y=4.14159265;
  printf("%f %f \n",x,y);
  return y;
}