Link errors with Boost port of header-only libraries for Emscripten in C++ / Wasm

Question

I'm trying to compile a cpp file to make some tests with the Boost library in a Wasm project by using the existing Emscripten port:

https://github.com/emscripten-ports/boost

When I use some of the Boost modules it works properly, like lambda in this example:

https://www.boost.org/doc/libs/1_75_0/more/getting_started/windows.html#build-a-simple-program-using-boost

But when I use other modules like locale in this example, I get compilation errors:

https://www.boost.org/doc/libs/1_48_0/libs/locale/doc/html/hello_8cpp-example.html

 D:\DANI\wasm\boostsuite>emcc boost_suite.cpp -s USE_BOOST_HEADERS=1 -s LLD_REPORT_UNDEFINED -o target/boost_suite.html
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::generator::generator()
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::generator::~generator()
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::generator::generate(std::__2::basic_string<char, std::__2::char_traits<char>, std::__2::allocator<char> > const&) const
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::ios_info::get(std::__2::ios_base&)
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::ios_info::display_flags(unsigned long long)
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::ios_info::get(std::__2::ios_base&)
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::ios_info::display_flags(unsigned long long)
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::ios_info::get(std::__2::ios_base&)
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::ios_info::display_flags(unsigned long long)
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::ios_info::get(std::__2::ios_base&)
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::ios_info::display_flags(unsigned long long)
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::ios_info::get(std::__2::ios_base&)
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::ios_info::domain_id() const
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::converter<char>::id
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::details::format_parser::format_parser(std::__2::ios_base&, void*, void (*)(void*, std::__2::locale const&))
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::details::format_parser::set_one_flag(std::__2::basic_string<char, std::__2::char_traits<char>, std::__2::allocator<char> > const&, std::__2::basic_string<char, std::__2::char_traits<char>, std::__2::allocator<char> > const&)
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::details::format_parser::get_position()
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::details::format_parser::~format_parser()
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::ios_info::get(std::__2::ios_base&)
    wasm-ld: error: C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o: undefined symbol: boost::locale::details::format_parser::restore()
    wasm-ld: error: too many errors emitted, stopping now (use -error-limit=0 to see all errors)
    emcc: error: 'D:/DANI/wasm/emsdk/upstream/bin\wasm-ld.exe -o target/boost_suite.wasm C:\Users\dani\AppData\Local\Temp\emscripten_temp_7wl1l58q\boost_suite_0.o -LD:\DANI\wasm\emsdk\upstream\emscripten\cache\sysroot\lib\wasm32-emscripten D:\DANI\wasm\emsdk\upstream\emscripten\cache\sysroot\lib\wasm32-emscripten\libboost_headers.a D:\DANI\wasm\emsdk\upstream\emscripten\cache\sysroot\lib\wasm32-emscripten\libgl.a D:\DANI\wasm\emsdk\upstream\emscripten\cache\sysroot\lib\wasm32-emscripten\libal.a D:\DANI\wasm\emsdk\upstream\emscripten\cache\sysroot\lib\wasm32-emscripten\libhtml5.a D:\DANI\wasm\emsdk\upstream\emscripten\cache\sysroot\lib\wasm32-emscripten\libc.a D:\DANI\wasm\emsdk\upstream\emscripten\cache\sysroot\lib\wasm32-emscripten\libcompiler_rt.a D:\DANI\wasm\emsdk\upstream\emscripten\cache\sysroot\lib\wasm32-emscripten\libc++-noexcept.a D:\DANI\wasm\emsdk\upstream\emscripten\cache\sysroot\lib\wasm32-emscripten\libc++abi-noexcept.a D:\DANI\wasm\emsdk\upstream\emscripten\cache\sysroot\lib\wasm32-emscripten\libdlmalloc.a D:\DANI\wasm\emsdk\upstream\emscripten\cache\sysroot\lib\wasm32-emscripten\libc_rt_wasm.a D:\DANI\wasm\emsdk\upstream\emscripten\cache\sysroot\lib\wasm32-emscripten\libsockets.a -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr --allow-undefined-file=C:\Users\dani\AppData\Local\Temp\tmp2cj831u_.undefined --strip-debug --export main --export emscripten_stack_get_end --export emscripten_stack_get_free --export emscripten_stack_init --export stackSave --export stackRestore --export stackAlloc --export __wasm_call_ctors --export fflush --export __errno_location --export malloc --export free --export setThrew --export-table -z stack-size=5242880 --initial-memory=16777216 --entry=main --max-memory=16777216 --global-base=1024' failed (1)

(both examples taken from the official documentation)

I compile the file with the -s USE_BOOST_HEADERS=1, which is the most straightforward way to do it as I have read in Emscripten ports documentation:

https://emscripten.org/docs/compiling/Building-Projects.html#emscripten-ports

https://emscripten.org/docs/getting_started/FAQ.html#how-do-i-link-against-system-libraries-like-sdl-boost-etc

emcc boost_suite.cpp -s USE_BOOST_HEADERS=1 -s LLD_REPORT_UNDEFINED -o target/boost_suite.html

It seems I'm missing some includes or links but I don't know how to add them to the emcc command so that the compilation works. I already have the Boost library installed in my computer.

Thanks in advance!

Dani P.

EDIT: I just opened an issue in GitHub if is a port problem:

https://github.com/emscripten-ports/boost/issues/3

~~EDIT 2: The problem has to do with the Boost libraries that are not header-only, this is why lambda example works but locale not:~~

https://www.boost.org/doc/libs/1_55_0/more/getting_started/windows.html#header-only-libraries

The no header-only libraries have to be compiled before included, but I don't know how to do it so it works with the emcc command. Any help please?

EDIT 2: I have checked that there is a locale.hpp file in the Boost folder so that it should work with the headers -s USE_BOOST_HEADERS=1.

I have tried adding this file and the locale folder to the compilation with -I but it doesn't work either, so I think it could be a port issue.

The goal is to have the compiled boost library in a `.a` file (or a bunch of `.o` files), then add that as a source file along with `boost_suite.cpp`. To get that static archive will depend on the library, but `emcmake cmake .. && emmake make` will often work. See https://emscripten.org/docs/compiling/Building-Projects.html#using-libraries — cajomar, Feb 25 '21 at 13:47
Thanks for your comment. I expected the whole Boost suite with all its libraries to be available in the Emscripten port but it only includes the headers, so I will have to compile and link the rest as you explain. I'm going to give it a try and I'll come back ;-) — Dani P., Feb 25 '21 at 21:24
I have come back to this issue and I have double checked that there is a file boost/locale.hpp which includes other hpp files in boost/locale. Therefore I assume I don't have to compile it and it should work with the `USE_BOOST_HEADERS=1`. Anyway I have tried adding it to the includes manually when compiling with `-I ../boost -I ../boost/locale` and it doesn't work either. More ideas? — Dani P., Mar 07 '21 at 11:59
Considering that the error is in the linking stage, it looks like boost locale library uses .cpp as well as the .hpp headers, so you'll need to compile the cpp files as well. — cajomar, Mar 07 '21 at 16:50

Link errors with Boost port of header-only libraries for Emscripten in C++ / Wasm

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