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I have a few simple C files that I would like to compile and use with cinterop, and I have a few que...
# multiplatform
c
I have a few simple C files that I would like to compile and use with cinterop, and I have a few questions 1. Is it possible to actually compile those C files as a part of my Gradle build? If so, what is the best way to go about it? 2. Assuming these C files compile to a static library and I include them in my Kotlin target, will they work on Android? Or do I need to write separate JNI bindings for Android, and then merge the interfaces into a cross-platform abstraction?
j
1. Yes, you create a cinterop setup as displayed here: https://kotlinlang.org/docs/native-app-with-c-and-libcurl.html#add-interoperability-to-the-build-process one thing should be noted, this will only work with native targets 2. They will work on android, but there is a lot of gotchas. You can't use the most heavy weight kotlin multiplatform libraries if you create a pure android native application (such as coroutines or atomicfu) or for obvious reasons, make use of the traditional android libraries. If you want to use jvm yes, your only choice here is to setup a separate JNI binding
c
@Joakim Forslund in that example 
libcurl
is not compiled as a part of the build, but rather the system 
libcurl
is linked from Kotlin
j
It sure is, they get compiled as a part of the cinterop setup
You will find the compiled files under build/cinterop, but maybe you mean something else.
c
From the link:
You need to have the 
curl
library binaries on your system to make the sample work.
It does not use Clang or GCC to compile 
libcurl
as a part of the Gradle build
j
Yes? And you just want to compile some files, the setup is still the same. Put the c files into the cinterop folder, but without the need to setup the obvious curl linking or include
Yeah, I'm not sure what you mean with Gradle build here.
The cinterop binaries will be located in the build folder as a part of the normal gradle build process
And the notion that it does not use clang to compile libcurl is just wrong
c
Okay, put another way Inside of the 
def
file, 
curl/curl.h
is put into the 
headers
field. If I have 
hello.c
and 
hello.h
, can I put a 
.c
file into the 
headers
field?
j
In that case your 
def
file would contain
Copy code
package = hello
headers = hello.h
headerFilter = hello.h
---
One way is to put your 
.c
code under the 
---
in the def file
If you want to keep your 
.c
file intact, you simply pass the folder where the c files is located to compilerOpts
c
I am able to get it working if the c code is below the 
---
, but I am unable to get it to work any other way
It fails with 
CXError_ASTReadError
if I put the 
.c
file in the arguments
I could use Gradle’s 
cpp-library
plugin to do the compile, and then 
cinterop
just for the headers
As most examples I have seen online either a) bundle a static library (
.a
) or b) link a system library
j
I have several projects there the folder of the c files gets passed in as compilerOpts. Try placing the 
.c
and the 
.h
file in the same folder i.e 
nativeInterop/cinterop/c
. Keep the same def file
c
actually, it worked if I just passed the 
.c
file in the 
headers
array
j
Sure, but interlinking issues might come from that
At any case, what I wrote above works, that I know.
c
Sweet, I will fiddle with it. Further question, if I want to use 
cinterop
on Android, I assume I need to use 
androidNativeArm64
and not just 
android
?
j
Yes
c
Because the functions are not 
static
(they are from an external library), I either get “symbol multiply defined” if I include the 
c
file or “symbol not found” if I do not
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