Which libraries do you need to link against for a clang program using blocks.

Question

I've discovered (below) that I need to use -fblocks when compiling code which uses blocks.

What library do I need to link against to let the linker resolve _NSConcreteStackBlock? (On Ubuntu 9.10 AMD64.)

Thanks,

Chris.

chris@chris-desktop:~$ clang ctest.c 

ctest.c:3:25: error: blocks support disabled - compile with -fblocks or pick a
      deployment target that supports them
void call_a_block(void (^blockptr)(int)) {
                        ^
ctest.c:11:19: error: blocks support disabled - compile with -fblocks or pick a
      deployment target that supports them
    call_a_block( ^(int y) { 
                  ^
2 diagnostics generated.
chris@chris-desktop:~$ clang ctest.c -fblocks
/tmp/cc-4sPSeO.o: In function `main':
ctest.c:(.text+0x79): undefined reference to `_NSConcreteStackBlock'
collect2: ld returned 1 exit status
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Answer 1

Clang doesn't yet provide an easy way to use blocks on platforms that don't have built-in operating system support (e.g., SnowLeopard). You can find some more information on the libdispatch project here: http://libdispatch.macosforge.org/ and on the compiler-rt project (which provides the blocks runtime) here: http://compiler-rt.llvm.org/ but this is not yet well packaged for Clang end users.

If you want to dig in a bit, the compiler-rt project does have the blocks runtime in it, and you can use that to build a library which will provide the NSConcreteStackBlock.