# Compiling Crystal shared libary on Windows **URL:** \ **Category:** Help & Support\ **Created:** [May 23, 2023, 8:10pm UTC](https://forum.crystal-lang.org/t/compiling-crystal-shared-libary-on-windows/5700 "2023-05-23T20:10:30Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Jay1](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/jay1/32/1486_2.png) [@Jay1](https://forum.crystal-lang.org/u/Jay1)\ **Post date:** [May 23, 2023, 8:10pm UTC](https://forum.crystal-lang.org/t/compiling-crystal-shared-libary-on-windows/5700/1 "2023-05-23T20:10:30Z")
I can compile a shared library for use in C using an example from stack overflow (questions/32916684) on Linux. For the life of me I can’t do the same on Windows using the Windows Crystal implementation and MSVC 2022 (cl.exe). Anyone any ideas if this is possible? The command on Linux is: crystal build --single-module --link-flags=“-shared” -o liblogger.so none of the cl.exe flags work in place of “-shared” though, and the various other approaches I tried. ---
**Author:** ![HertzDevil](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/hertzdevil/32/1023_2.png) [@HertzDevil](https://forum.crystal-lang.org/u/HertzDevil)\ **Post date:** [May 23, 2023, 8:28pm UTC](https://forum.crystal-lang.org/t/compiling-crystal-shared-libary-on-windows/5700/2 "2023-05-23T20:28:26Z")
`--link-flags=/DLL -o logger.dll` However, as you might have noticed, the Crystal runtime is not really prepared for use as a shared library yet. Additionally, currently this will build a DLL that links to the Microsoft C runtime statically (i.e. `/MT`), which is discouraged. ---
**Author:** ![Jay1](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/jay1/32/1486_2.png) [@Jay1](https://forum.crystal-lang.org/u/Jay1)\ **Post date:** [May 23, 2023, 8:59pm UTC](https://forum.crystal-lang.org/t/compiling-crystal-shared-libary-on-windows/5700/3 "2023-05-23T20:59:40Z")
It does produce a DLL, I tried this flag earlier. A dumpbin /EXPORTS liblogger.dll shows no exported functions strangely. A lib file is also not produced which can be linked against it. There doesn’t seem to be any compiler flags for crystal build to pass “/LD” to get a lib file. ---
**Author:** ![HertzDevil](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/hertzdevil/32/1023_2.png) [@HertzDevil](https://forum.crystal-lang.org/u/HertzDevil)\ **Post date:** [May 23, 2023, 9:18pm UTC](https://forum.crystal-lang.org/t/compiling-crystal-shared-libary-on-windows/5700/4 "2023-05-23T21:18:03Z")
Exactly. If `-shared` produces a file that exports something on Linux that is also by sheer coincidence rather than by design. ---
**Author:** ![Jay1](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/jay1/32/1486_2.png) [@Jay1](https://forum.crystal-lang.org/u/Jay1)\ **Post date:** [May 23, 2023, 9:26pm UTC](https://forum.crystal-lang.org/t/compiling-crystal-shared-libary-on-windows/5700/5 "2023-05-23T21:26:07Z")
Fixed it. If I use --verbose I can see the command it is running with cl.exe - I can then modify that and add /LD and /DEF:liblogger.def on the end. I had to create a def file manually. I got the functions to use in the def file from nm liblogger.obj | grep crystal\_ in WSL. Complete command is: C:\Program Files (x86)\Microsoft Visual Studio\2022\BuildTools\VC\Tools\MSVC\14.36.32532\bin\Hostx64\x64\cl.exe" /nologo /LD liblogger.obj /link “/LIBPATH:C:\Program Files (x86)\Microsoft Visual Studio\2022\BuildTools\VC\Tools\MSVC\14.36.32532\atlmfc\lib\x64” “/LIBPATH:C:\Program Files (x86)\Microsoft Visual Studio\2022\BuildTools\VC\Tools\MSVC\14.36.32532\lib\x64” “/LIBPATH:C:\Program Files (x86)\Windows Kits\10\Lib\10.0.22000.0\ucrt\x64” “/LIBPATH:C:\Program Files (x86)\Windows Kits\10\Lib\10.0.22000.0\um\x64” /DEBUG:FULL /PDBALTPATH:%\_PDB% /INCREMENTAL:NO /STACK:0x800000 /LIBPATH:C:\Users\jools\scoop\apps\crystal\current\lib pcre2-8.lib gc.lib libcmt.lib iconv.lib advapi32.lib Kernel32.lib shell32.lib ole32.lib WS2\_32.lib kernel32.lib legacy\_stdio\_definitions.lib DbgHelp.lib libucrt.lib /DEF:liblogger.def Churns out: Creating library liblogger.lib and object liblogger.exp Then: C:\Users\jools\tmp\crystal\>main.exe Hello world! ---
**Author:** ![Jay1](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/jay1/32/1486_2.png) [@Jay1](https://forum.crystal-lang.org/u/Jay1)\ **Post date:** [May 23, 2023, 9:28pm UTC](https://forum.crystal-lang.org/t/compiling-crystal-shared-libary-on-windows/5700/6 "2023-05-23T21:28:10Z")
And for anyone else: C:\Users\jools\tmp\crystal\>more liblogger.def LIBRARY liblogger EXPORTS \_\_crystal\_main \_\_crystal\_malloc \_\_crystal\_malloc64 \_\_crystal\_malloc\_atomic \_\_crystal\_malloc\_atomic64 \_\_crystal\_once \_\_crystal\_once\_init \_\_crystal\_raise \_\_crystal\_raise\_overflow \_\_crystal\_raise\_string \_\_crystal\_realloc \_\_crystal\_realloc64 crystal\_init crystal\_log C:\Users\jools\tmp\crystal\>more logger.cr fun init = crystal\_init : Void GC.init LibCrystalMain.\_\_crystal\_main(0, Pointer(Pointer(UInt8)).null) end fun log = crystal\_log(text: UInt8\*): Void puts String.new(text) end C:\Users\jools\tmp\crystal\>more logger.h #ifndef \_CRYSTAL\_LOGGER\_H #define \_CRYSTAL\_LOGGER\_H void crystal\_init(void); void crystal\_log(char\* text); #endif C:\Users\jools\tmp\crystal\>more main.c #include “logger.h” int main(void) { crystal\_init(); crystal\_log(“Hello world!”); } ---
**Author:** ![Jay1](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/jay1/32/1486_2.png) [@Jay1](https://forum.crystal-lang.org/u/Jay1)\ **Post date:** [May 23, 2023, 9:39pm UTC](https://forum.crystal-lang.org/t/compiling-crystal-shared-libary-on-windows/5700/7 "2023-05-23T21:39:43Z")
A complete run: crystal build logger.cr --single-module --emit obj --verbose mv logger.obj liblogger.obj Copy command and remove /ENTRY:wmainCRTStartup ; add /LD and /DEF:liblogger.def ; to get: “C:\Program Files (x86)\Microsoft Visual Studio\2022\BuildTools\VC\Tools\MSVC\14.36.32532\bin\Hostx64\x64\cl.exe” /nologo /LD liblogger.obj /link “/LIBPATH:C:\Program Files (x86)\Microsoft Visual Studio\2022\BuildTools\VC\Tools\MSVC\14.36.32532\atlmfc\lib\x64” “/LIBPATH:C:\Program Files (x86)\Microsoft Visual Studio\2022\BuildTools\VC\Tools\MSVC\14.36.32532\lib\x64” “/LIBPATH:C:\Program Files (x86)\Windows Kits\10\Lib\10.0.22000.0\ucrt\x64” “/LIBPATH:C:\Program Files (x86)\Windows Kits\10\Lib\10.0.22000.0\um\x64” /DEBUG:FULL /PDBALTPATH:%\_PDB% /INCREMENTAL:NO /STACK:0x800000 /LIBPATH:C:\Users\jools\scoop\apps\crystal\current\lib pcre2-8.lib gc.lib libcmt.lib iconv.lib advapi32.lib Kernel32.lib shell32.lib ole32.lib WS2\_32.lib kernel32.lib legacy\_stdio\_definitions.lib DbgHelp.lib libucrt.lib /DEF:liblogger.def cl main.c /link liblogger.lib C:\Users\jools\tmp\crystal\>main.exe Hello world!