Multifile/CMake feedback thread

[partouf]

We have implemented a way for you to compile programs using multiple files, and if it's C/C++ code, you can make the files link to each other through CMake.

Current implementation details

• The executable or library that your CMake configuration creates is assumed to be output.s unless you specify it in the UI
• If you don't enable CMake your main source file should be called example.cpp (in case of C++ ) and you'll need to change the extension to if you're using a different language
• You can use libraries, but to link against them you'll need to add a target_link_libraries() call manually to your CMakeLists.txt

Examples that can get you started

• https://godbolt.org/z/bM7oMhMY6
• https://godbolt.org/z/j1Wq97h5Y

[claremacrae]

I tried the first example on iPad in Safari …
Clicking on a file name didn’t seem to do anything- it didn’t load the file…
Clicking on the “edit” button (I assume that’s what the pencil is) also didn’t edit…
However, clicking on the trash icon did remove the file from the list.

I don’t know if you were expecting it to work on ipad, but thought I should log it just in case…

[partouf]

The pencil is indeed Edit, but it currently doesn't bring-to-front an existing editor (will require some hacking of Golden Layout). If the file tab was closed (and it has a filename), you should get it to open and focus.

[partouf]

I have now fixed this, thanks for the reminder!

[peterschussheim]

@partouf Patrick: this is AWESOME! I just discovered this feature now and will update with feedback after I play around with it. Thank you!

[rcombs]

Seems not to be working for MSVC yet? It tries to compile CMake files as C++, and when I disable cmake it isn't able to include header files I add ("No such file or directory").

[mattgodbolt]

MSVC support is handled separately by our friends at Microsoft, and the features tend to lag. They use our codebase, but host and update separately. We shell out to their compilers (somewhat transparently), but it does mean we need to hold off on them updating and ensuring the CMake code works for them too.

[partouf]

A while back, someone posted a useful guide for CE & CMake @ https://ggulgulia.medium.com/compiler-explorer-with-cmake-94fd38d5012f

[ed-gh]

very nice indeed!

One question though: What does one need to add to the CMakeLists.txt file to include and link libs like googletest ?
There are (href-links to) working examples out there illustrating how to apply the compiler option in non-IDE-mode, but how to make it work here: https://godbolt.org/z/qvnrdWbbe ?

(Two lines which apparently will not do the trick have been commented out from the CMakeLists.txt file.)

[partouf]

target_link_libraries() is the correct approach, but you hit a feature that specifically requires -pthread
https://godbolt.org/z/T7qsqhr8v

I know the warnings are pretty burried, but it was sort of clear from that:

gnu/bin/ld: /app/libgtestd.a(gtest-all.cc.o): in function `testing::internal::ThreadLocal<testing::TestPartResultReporterInterface*>::~ThreadLocal()':
gtest-all.cc:
(.text._ZN7testing8internal11ThreadLocalIPNS_31TestPartResultReporterInterfaceEED2Ev[_ZN7testing8internal11ThreadLocalIPNS_31TestPartResultReporterInterfaceEED5Ev]+0x15): undefined reference to `pthread_getspecific'

The /app/libgtestd.a mention means that it was linked to the static library that we provide,
And the undefined reference to 'pthread_getspecific' indicating that it was looking for a symbol named pthread_getspecific, which somewhat obviously belongs to pthread, and using -lpthread or -pthread you can link to pthread, which provides that symbol.

Not all google test "things" require pthread, so we don't add it by default.

[ed-gh]

This worked like a charm, thank you, much appreciated!

Now running into a slightly similar issue when trying to include and link to Xerces-C, which seems to depend on libcurl, and I'm still way too inexperienced with CMake to solve this (assuming the missing step is in there). Would you mind giving it a look?
https://godbolt.org/z/v85aG4aGb

[partouf]

Hi @ed-gh we added Curl to our library list yesterday so this should work now https://godbolt.org/z/z4EoYrhsM

[ed-gh]

Excellent, thank you very much.

[lackhoa]

I find the option to upload zip source code very helpful. However the file doesn't seem to reload if you upload a new zip?

[partouf]

Sorry for the lack of response, but we did manage to fix this last month!

[StanHB]

I don't see a way to add additional cmake files for scripts. We seem to just get one CMakelists.txt. It might be useful to have a way to just run cmake on its own - as a script language not as a means to organize c++ builds.

[partouf]

You can save a file as anything in any path. I've seen people save files as something.cmake and/or as src/subdir/CMakeLists.txt, but you can combine both. Basically you have full control over anything within CMake.

But we do try to keep everything user-friendly within reason, if you want different languages than C/C++/Fortran, it starts to get complicated really fast.

For other languages I would see more in trying to support their own domain buildsystems.

[StanHB]

Yes, this worked for me. But I have to fake the file as some other language type in the editor.
It would be nice if the editor recognized or allowed us to choose cmake as a file's language.
And thinking along those lines if we just had a way to run CE with cmake as the "compiler" on cmake scripts it would be a useful way to play with cmake language outside a project to build some c/c++.

[partouf]

Someone recently made a set of CMake files to chain Cpp2-cppfront to a regular C++ compiler https://godbolt.org/z/dT87zrWbP - from modern-cmake/cppfront#1

[JohelEGP]

Here's an up-to-date link: https://cpp2.godbolt.org/z/4PE6dTY8f.
(For more up-to-date links, check out my bug reports at https://github.com/hsutter/cppfront/issues).

[partouf]

Example of a cmake that compiles c/c++ along with some nasm https://godbolt.org/z/qqW1KWhhq

[partouf]

Earlier this year this video was posted by @lefticus about showing LTO effects via CMake in CE https://www.youtube.com/watch?v=pyiKhRmvMF4

[partouf]

We recently installed a new CMake that makes things easier yet again to make c++ modules work;

Via https://twitter.com/bretbrownjr/status/1640786959801917453

Without too much trouble in your cmake file; https://godbolt.org/z/von5MfK7T

Doesn't work for gcc yet, unfortunately.

More info at https://www.kitware.com/import-cmake-c20-modules/

[bretbrownjr]

Necro comment: GCC trunk just landed the required changes to make this work.

[DESX]

Getting "cannot find library" linker error when using target_link_libraries. Looks like the same examples posted earlier are showing same linker error: https://godbolt.org/z/5cP9qEzh7. Tried different compiler versions and different libraries. Can't get any libraries to link using CMake.

[partouf]

There are a couple things going on here, but I'm on my phone it's a little hard to go back and forth. But the main source here to double check the availability for compiler, library and filenames in there can be found at https://conan.compiler-explorer.com/libraries_cpp.html

You can lookup the library and version, if you cant find the version it either header only, or we havent ever built it (succesfully).

If you can find it you can click on it and you'll see the list of compilers its available for, and then click on that to see the manifest which can tell you which files were built.

[DESX]

Ok, so trying to get libfmt working with CMake:

Under libfmt 10.0.0, it Lists it being built for x86_64 libstdc++ under gcc10.1. The conan_package.tgz contains lib/libfmtd.a.

This would lead me to expect target_link_libraries(fmt_test PUBLIC fmtd) To link in the library. It seems to be finding the header, just a linker error. Would I need to add some location to my CMake library path to get it working, and if so how would I find that path? Here is my non-working attempt: https://godbolt.org/z/asPYbP7d7. I am fairly confident I had the same CMake example working in the past. Is it possible something changed?

[partouf]

Seems you found a bug. Yes, we did change it recently and aparantly made a mistake.
Workaround is this https://godbolt.org/z/fbPPb76b7
But I'm going to fix this asap.

[DESX]

Glad I could contribute by finding a bug. Sincere gratitude to you and the other CE contributors. It is such a fantastic tool!

[partouf]

this is now fixed live, thanks again!

[denchat]

Workaround is this https://godbolt.org/z/fbPPb76b7

When changed into gcc 11 and above, gtest library is missing reportedly.

/opt/compiler-explorer/gcc-11.4.0/bin/../lib/gcc/x86_64-linux-gnu/11.4.0/../../../../x86_64-linux-gnu/bin/ld: cannot find -lgtestd: No such file or directory
/opt/compiler-explorer/gcc-11.4.0/bin/../lib/gcc/x86_64-linux-gnu/11.4.0/../../../../x86_64-linux-gnu/bin/ld: cannot find -lgtest_maind: No such file or directory
collect2: error: ld returned 1 exit status

When changed into gcc 13 and above, Catch2 library is also missing reportedly.

/opt/compiler-explorer/gcc-13.2.0/bin/../lib/gcc/x86_64-linux-gnu/13.2.0/../../../../x86_64-linux-gnu/bin/ld: cannot find -lgtestd: No such file or directory
/opt/compiler-explorer/gcc-13.2.0/bin/../lib/gcc/x86_64-linux-gnu/13.2.0/../../../../x86_64-linux-gnu/bin/ld: cannot find -lgtest_maind: No such file or directory
/opt/compiler-explorer/gcc-13.2.0/bin/../lib/gcc/x86_64-linux-gnu/13.2.0/../../../../x86_64-linux-gnu/bin/ld: cannot find -lCatch2d: No such file or directory
collect2: error: ld returned 1 exit status

clang 14 works fine, while clang 16 and above are missing gtest library.

/opt/compiler-explorer/gcc-12.2.0/lib/gcc/x86_64-linux-gnu/12.2.0/../../../../x86_64-linux-gnu/bin/ld: cannot find -lgtestd: No such file or directory
/opt/compiler-explorer/gcc-12.2.0/lib/gcc/x86_64-linux-gnu/12.2.0/../../../../x86_64-linux-gnu/bin/ld: cannot find -lgtest_maind: No such file or directory
clang-16: error: linker command failed with exit code 1 (use -v to see invocation)

[LIVE]

clang seems missing curl when compiled with libc++ too.

/opt/compiler-explorer/gcc-11.2.0/lib/gcc/x86_64-linux-gnu/11.2.0/../../../../x86_64-linux-gnu/bin/ld: cannot find -lcurl-d
clang-14: error: linker command failed with exit code 1 (use -v to see invocation)

[LIVE]

[partouf]

It appears gtest doesn't build under Clang 16 because they have -Werror in combination with -Wunused-command-line-argument
https://conan.compiler-explorer.com/getlogging/20230319020258
Not sure if fixable, because we do have to pass linker flags and we need it to always work.

[jpvanoosten]

Does anyone have an example of this working with MSVC without CMake but with multiple .cpp files?

[kimmywork]

Any example of this in Java/Scala?

[partouf]

We do for Java, we even have a site template for it: https://godbolt.org/z/Y3nKarh87
There's something wrong with the language selection, so Scala is not available at the moment

[joergbrech]

I tried a multi file project using the cpptrace library, but I am getting linker errors. What am I doing wrong? https://godbolt.org/z/fvjve1YhP

[joergbrech]

Nevermind, figured it out https://godbolt.org/z/hhbj94z8Y. Not sure why I had to add transitive dependencies here, but I don't care, it works for me.

[bretbrownjr]

You won't automatically get transitive dependencies in CMake unless you use something like find_package(foobar REQUIRED) and then target_link_libraries(myprogram PRIVATE foobar::foobar) later on.

I don't believe compiler explorer installs the CMake modules that implement this sort of logic. Instead, you have to hardcode your compile flags and link flags to work with the transitive set of your dependencies.

Installing the CMake modules to import library dependencies properly would be a great enhancement to Compiler Explorer. The docs for find_package describe where CMake expects to be able to find those files when they are installed.