C++ support in nrf9160 modem_key_mgmt library

[Miro Petrak]

Env:

• gcc version 10.3.1 20210824 (release) (GNU Arm Embedded Toolchain 10.3-2021.10)
• std=c++11
• nRF Connect SDK v2.0.0

C++ project won't build with modem_key_mgmt library:

undefined reference to `modem_key_mgmt_write(unsigned int, modem_key_mgmt_cred_type, void const*, unsigned int)'
collect2.exe: error: ld returned 1 exit status

modem_key_mgmt.h is missing 

#ifdef __cplusplus
extern "C" {
#endif
...
#ifdef __cplusplus
}
#endif

[Øyvind]

Hello, 
the DevZone team and Nordic Semiconductor are currently entering summer vacation period, some delays in answers must be expected due to lower staffing during this period. We apologies for the inconvenience. 

---

Unless you have a very specific reason for using C++ in you project, we recommend building with C. This is what most of the nRF Connect SDK is based upon. The modem library is based on Newlib C. The Modem Key Management uses AT commands to add, update, and delete credentials, which again is modelled after the printf() and scanf() C library functions.

Kind regards,
Øyvind

[Miro Petrak]

It's just a matter of adding mentioned code block

#ifdef __cplusplus
extern "C" {
#endif
...
#ifdef __cplusplus
}
#endif

12 out of 14 header files in nrf/include/modem have it

./at_cmd_parser.h
./at_monitor.h
./at_params.h
./location.h
./lte_lc.h
./lte_lc_trace.h
./modem_attest_token.h
./modem_info.h
./modem_jwt.h
./nrf_modem_lib.h
./pdn.h
./sms.h

except

./modem_key_mgmt.h
./nrf_modem_lib_trace.h

[Øyvind]

Thanks for clarifying. I have forwarded to our developers.

[Øyvind]

The issue has already been addressed in this Github PR