--- gctp/src/gctp.c.orig	2013-07-23 03:28:51.000000000 +0900
+++ gctp/src/gctp.c	2020-11-22 10:57:55.000000000 +0900
@@ -33,6 +33,12 @@
 #include "cproj.h"
 #include "proj.h"
 
+extern int for_init( int, int, double*, int, char *, char *, int *, int (*for_trans[])(double, double, double *, double *));
+extern void close_file(void);
+extern int init(long, long, char *, char *);
+extern long untfz(long, long, double *);
+extern inv_init(int, int, double *, int, char *, char *, int *, int (*inv_trans[])(double, double, double*, double*));
+
 #define TRUE 1
 #define FALSE 0