"C++ Example using CMake" in latest documentation and main branch is broken

[dok-net]

https://nuttx.apache.org/docs/latest/guides/cpp_cmake.html states:

Using the ‘build as a library’ procedure of NuttX, it is possible to build NuttX applications using C++ language and also the cmake build tool.

This is not correct, at least on Ubuntu "jammy" or "" (toolchain Ubuntu (deb) as per Installing/Toolchain).
Using pristine git checkouts (but "download stable release" fares no better), plus make distclean, then following the instructions to the word, there are multiple obvious issues.

The include files cstdio and string are not found.
The exported tar archive does not contain the libs board, gcc (IIRC), supc++.

At least the sim target should be supported for this out-of-tree CMake-based build procedure and documented in the step-by-step tutorial style.

With the later C++ releases, more exactly the standard library, I think they are a great showcase for the POSIX support in NUTTX.

[acassis]

@dok-net thank you for reporting the issue. This Guide was written by @fraviofii ! I'll ask him to review it.

[fdcavalcanti]

@dok-net did you manage to compile from a export? Just had the same issue as you.

[dok-net]

@fdcavalcanti Has there been any activity on this issue? I keep checking regularly. No changes, no improvement.

[fdcavalcanti]

Got it to work with a few modification for my board (TM4C):

• src/CMakeLists.txt:

1. • Commented the linking of supc++
2. • libgcc had to be linked with a harcoded path such as "/usr/lib/gcc/arm-none-eabi/10.3.1/thumb/v7e-m+fp/softfp/libgcc.a"
3. • libxx requires the user to activate the use of C++ on make menuconfig
4. • On "add_custom_command" I had to change the .elf directory that was missing /src/.

set(HEADER_FILES
    HelloWorld.h
)

set(SOURCE_FILES
    HelloWorld.cpp
)

link_directories(${EXE_NAME} ${NUTTX_PATH}/libs)

add_executable(${EXE_NAME} ${SOURCE_FILES} main.cpp ${HEADER_FILES})

add_custom_command(
        TARGET ${EXE_NAME}
        POST_BUILD
        COMMAND ${CMAKE_OBJCOPY} ARGS -S -O binary ${CMAKE_BINARY_DIR}/src/ ${EXE_NAME}.elf ${CMAKE_BINARY_DIR}/${EXE_NAME}.bin
)
message(CMAKE_BINARY_DIR=${CMAKE_BINARY_DIR})

target_link_libraries(${EXE_NAME} --start-group)

target_link_libraries(${EXE_NAME} sched)
target_link_libraries(${EXE_NAME} drivers)
target_link_libraries(${EXE_NAME} boards)
target_link_libraries(${EXE_NAME} c)
target_link_libraries(${EXE_NAME} mm)
target_link_libraries(${EXE_NAME} arch)
target_link_libraries(${EXE_NAME} xx)
target_link_libraries(${EXE_NAME} apps)
target_link_libraries(${EXE_NAME} fs)
target_link_libraries(${EXE_NAME} binfmt)
target_link_libraries(${EXE_NAME} board)
target_link_libraries(${EXE_NAME} net)
target_link_libraries(${EXE_NAME} "/usr/lib/gcc/arm-none-eabi/10.3.1/thumb/v7e-m+fp/softfp/libgcc.a")
# target_link_libraries(${EXE_NAME} supc++)

target_link_libraries(${EXE_NAME} --end-group)

• CMakeLists.txt:

1. Modified include/libcxx to include/cxx

I think that was it. I had some issues with linking to boards and net, but not sure why it works now.
I also could not get hard-abi to work.
Finally, had to comment the include of string because:

/home/filipe/hellonuttx/src/HelloWorld.cpp:2:10: fatal error: string: No such file or directory
    2 | #include <string>

[dok-net]

I think that was it. I had some issues with linking to boards and net, but not sure why it works now.
I also could not get hard-abi to work.

"Some issues" :-) I have adapted your changes but due to this problem the issue is still unresolved. It doesn't spontaneously succeed by random chance here.

libxx requires the user to activate the use of C++ on make menuconfig

Could you please be specific on this?

[fdcavalcanti]

Hey @dok-net, sorry to keep you waiting.
By activate C++ on menuconfig I meant to go in "Library Routines -> Have C++ compiler" and check this entry.

Regarding the "linking boards and net", I noticed the libboard.a was missing, however libboards.a was present. I had to go on the NuttX dir, compile everything as usual and copy the now available libboard.a file to the exported app.

filipe@fdcavalcanti:~/nuttxspace/nuttx$ find . -name "*board*.a"
./boards/libboards.a
./staging/libboards.a
filipe@fdcavalcanti:~/nuttxspace/nuttx$ make -j
CPP:  /home/filipe/nuttxspace/nuttx/boards/arm/tiva/tm4c1294-launchpad/scripts/ld.script-> /home/filipe/nuttxspace/nutLD: nuttx
CP: nuttx.bin
filipe@fdcavalcanti:~/nuttxspace/nuttx$ find . -name "*board*.a"
./boards/arm/tiva/tm4c1294-launchpad/src/libboard.a
./boards/libboards.a
./staging/libboards.a

[trns1997]

@fdcavalcanti i came across the exact same issue where libboard.a is missing. There seems to be a bug with make export when used directly after configuring your board. The way to by pass this bug (i am guessing it is a bug) for the moment is to to call make right before calling make export. The problem seems to have already been resolved in the past #7232 but i am guessing something changed since. Here is a link to my issue: #10388

[acassis]

@trns1997 @dok-net @fdcavalcanti I think we need to include "make export" in the CI and run some basic SIM build test using C++ to confirm it is working.

[trns1997]

@acassis if I understand correctly, you are suggesting we create a test cpp project that consumes the output (archive) generated by make export to test if the export was successful? Couldn't we simply check that the files generated from the export are all there? Just a suggestion not sure which one is a better approach.

[fdcavalcanti]

I think that would be a good approach. I would like to also point out that this is behaviour for the basic C++ compiler. When using LLVM there is another issue pointed in #5530 that I think is relevant to the discussion.

[trns1997]

@fdcavalcanti check out the following PR #10398. It automatically generates a cmake toolchainfile that you can use to build cpp applications. Note this does not solve the make export problem. I will look into that when i have the time.