如何将本地 C 库构建为静态库并与 Swift 链接？

Question

As the title suggests, I am having a bit of trouble creating a static library from C code and having it used in a Swift project.

Here is the make process for the C-Code:

make
# Making the static library
clang -c Sources/nuklear.c -o nuklear.o
clang -c Sources/test.c -o test.o
libtool -static nuklear.o test.o -o libNuklear.a
cp libNuklear.a /usr/local/lib
❯ ls /usr/local/lib | grep Nuk
libNuklear.a

Here is the error:

swift build -Xlinker -L/usr/local/lib
'CNuklear' /Users/pprovins/Projects/CNuklearTest/.build/checkouts/CNuklear: warning: system packages are deprecated; use system library targets instead
ld: warning: Could not find or use auto-linked library 'libNuklear'
Undefined symbols for architecture x86_64:
  "_test_doit", referenced from:
      _main in main.swift.o
ld: symbol(s) not found for architecture x86_64
[0/1] Linking CNuklearTest

The error suggests the library cannot be found or the library is not usable (unable to determine which).

Running nm on libNuklear.a reveals:

libNuklear.a(test.o):
                 U _printf
0000000000000000 T _test_doit

It appears the symbols do exist, so I am leaning toward the possibility of it being an issue finding the library to link against so I shall describe my bridging process next. The C-Code is placed in a system-library module/package separate from the executable being built. It contains a bridging header and package definition. Here is the module.modulemap definition:

module CNuklear [system] {
  header "Includes/CNuklear.h"
  link "libNuklear"
  export *
}

The bridging header ( CNuklear.h ):

#import "Includes/nuklear.h"
#import "Includes/test.h"

I currently make the static library, then attempt to build the swift executable; however, it is having trouble linking against the static library I have made. Here is how I am attempting to include and execute the code in main.swift :

import CNuklear

test_doit()

print("Hello, world!")

Is there a way to further debug the issue with linking that I am having? Thanks in advance!

Answer 1

In the module.modulemap file:

If the static library being built is named libNuklear.a , the link specification for the module must be:

module CNuklear [system] {
  header "Includes/CNuklear.h"
  link "Nuklear"
  export *
}

You must also run swift build with -Xlinker -L/usr/local/lib or -Xlinker -L/dir/which/lib/resides