Using both c stdio and zephyr stdio

[nateyoung]

Hello,

I am developing an application that requires use of some of the traditional C "stdio.h" functionality. My current development setup is the nRF5340 DK running Zephyr OS v2.7.99. I am attempting to use the dr_libs libraries, particularly dr_wav at the moment, for decoding audio files. These libraries depend on standard C stdio.h, and I am unsure how to properly include this and other standard C headers in my project. I currently have dr_wav.h placed in my app src right next to src/main.c. I'm also unsure the best way to keep external sources separate from my own in the project organization.

So far I have tried adding the include path (from the toolchain) to my project by using "include_directories()" in my CMakeLists.txt:

cmake_minimum_required(VERSION 3.20.0)

set(BOARD nrf5340dk_nrf5340_cpuapp)

find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})

project(490B_proj)

FILE(GLOB app_sources src/*.c src/*.h)

include_directories(C:/Users/njyou/ncs/v1.9.0/toolchain/opt/arm-none-eabi/include)

target_sources(app PRIVATE ${app_sources})

And VS Code will now recognize that there are two stdio.h available, one from zephyr and one from standard C:

But still, when trying to call dr_wav_init_file() in main.c, I get the following build errors:

c:/users/njyou/ncs/v1.9.0/toolchain/opt/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/bin/ld.exe: app/libapp.a(main.c.obj): in function `drwav__on_seek_stdio':
C:\Users\njyou\school\s22\490B\490b_ws\490b_ws\490b_app\src\dr_wav.h:4802: undefined reference to `fseek'
c:/users/njyou/ncs/v1.9.0/toolchain/opt/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/bin/ld.exe: app/libapp.a(main.c.obj): in function `fread':
C:\Users\njyou\ncs\v1.9.0\toolchain\opt\arm-none-eabi\include\ssp\stdio.h:88: undefined reference to `fread'
c:/users/njyou/ncs/v1.9.0/toolchain/opt/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/bin/ld.exe: app/libapp.a(main.c.obj): in function `drwav__on_read':
C:\Users\njyou\school\s22\490B\490b_ws\490b_ws\490b_app\src\dr_wav.h:3734: undefined reference to `__assert_func'
c:/users/njyou/ncs/v1.9.0/toolchain/opt/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/bin/ld.exe: app/libapp.a(main.c.obj): in function `drwav_fopen':
C:\Users\njyou\school\s22\490B\490b_ws\490b_ws\490b_app\src\dr_wav.h:3742: undefined reference to `__errno'
c:/users/njyou/ncs/v1.9.0/toolchain/opt/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/bin/ld.exe: app/libapp.a(main.c.obj): in function `drwav__metadata_get_memory':
C:\Users\njyou\school\s22\490B\490b_ws\490b_ws\490b_app\src\dr_wav.h:3804: undefined reference to `__assert_func'
c:/users/njyou/ncs/v1.9.0/toolchain/opt/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/bin/ld.exe: app/libapp.a(main.c.obj): in function `drwav__metadata_process_info_text_chunk':
C:\Users\njyou\school\s22\490B\490b_ws\490b_ws\490b_app\src\dr_wav.h:3826: undefined reference to `__assert_func'
c:/users/njyou/ncs/v1.9.0/toolchain/opt/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/bin/ld.exe: app/libapp.a(main.c.obj): in function `drwav__metadata_copy_string':
C:\Users\njyou\school\s22\490B\490b_ws\490b_ws\490b_app\src\dr_wav.h:3832: undefined reference to `__assert_func'
c:/users/njyou/ncs/v1.9.0/toolchain/opt/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/bin/ld.exe: app/libapp.a(main.c.obj): in function `drwav_buffer_reader_read':
C:\Users\njyou\school\s22\490B\490b_ws\490b_ws\490b_app\src\dr_wav.h:3893: undefined reference to `__assert_func'
c:/users/njyou/ncs/v1.9.0/toolchain/opt/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/bin/ld.exe: app/libapp.a(main.c.obj): in function `drwav_buffer_reader_read_u16':
C:\Users\njyou\school\s22\490B\490b_ws\490b_ws\490b_app\src\dr_wav.h:3936: undefined reference to `__assert_func'
c:/users/njyou/ncs/v1.9.0/toolchain/opt/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/bin/ld.exe: app/libapp.a(main.c.obj):C:\Users\njyou\school\s22\490B\490b_ws\490b_ws\490b_app\src\dr_wav.h:3946: more undefined references to `__assert_func' follow
c:/users/njyou/ncs/v1.9.0/toolchain/opt/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/bin/ld.exe: app/libapp.a(main.c.obj): in function `drwav_init_file__internal_FILE':
C:\Users\njyou\school\s22\490B\490b_ws\490b_ws\490b_app\src\dr_wav.h:4825: undefined reference to `fclose'
c:/users/njyou/ncs/v1.9.0/toolchain/opt/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/bin/ld.exe: app/libapp.a(main.c.obj): in function `drwav_fopen':
C:\Users\njyou\school\s22\490B\490b_ws\490b_ws\490b_app\src\dr_wav.h:4673: undefined reference to `fopen'
collect2.exe: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.
FATAL ERROR: command exited with status 1: 'c:\Users\njyou\ncs\v1.9.0\toolchain\opt\bin\cmake.EXE' --build 'c:\Users\njyou\school\s22\490B\490b_ws\490b_ws\490b_app\build'
The terminal process terminated with exit code: 1.

My question is then, what is the appropriate way to enable use of some of the standard C libraries in my project and remove these dependency issues? Any guidance is greatly appreciated, and please let me know if I can provide any more information to help.

[Susheel Nuguru]

These seems like linker error. So most likely the compiler found the declarations from your C files, but is not able to find the definitions of those while linking.
Check the example \zephyr\samples\application_development\external_lib and check the CMakeLists.txt file. You will have to use add_library to import external library and not just the header files.

[nateyoung]

Hello, thank you for the reply. I have looked into your suggestion. Do you mean to follow the application_development example and import the dr_wav.h external library or import the C stdio.h as an external library? I have tried both but am not sure where to point the src_dir because in the case of dr_wav.h there is no other source, and in the case of the C standard lib I am not sure where to find the actual definitions in the toolchain.

[Susheel Nuguru]

Those libraries seems to be outside the scope our solutions so I am guessing that you need to install/include this library from other sources. I can see that MinGW or GLFW might have these libraries included. Once you have install them, 

[nateyoung]

Hi, the fix I found was to set

CONFIG_NEWLIB_LIBC=y in proj.conf to enable use of the non-minimal c functionality. Although I ended up not needing this functionality. Thank you for the help.