Fix #224485 reported by Todd Denniston

libmodbus does not link with c++ code.

NEWS

@@ -27,6 +27,8 @@ libmodbus 1.9.x
   modbus.h is not installed at prefix.
 - Fix #211460 reported by Todd Denniston
   With TCP, automatic reconnect on error may not be desired.
+- Fix #224485 reported by Todd Denniston
+  libmodbus does not link with c++ code.
 
 libmodbus 1.2.4 (2008-03-14)
 - Fix #191039 reported by Todd Denniston

modbus/modbus.h

@@ -24,6 +24,10 @@
 #include <termios.h>
 #include <arpa/inet.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif 
+
 #define MODBUS_TCP_DEFAULT_PORT 502
 
 #define HEADER_LENGTH_RTU           0
@@ -303,4 +307,8 @@ void set_bits_from_bytes(uint8_t *dest, int address, int nb_bits,
    To obtain a full byte, set nb_bits to 8. */
 uint8_t get_byte_from_bits(const uint8_t *src, int address, int nb_bits);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif  /* _MODBUS_H_ */