What does “typedef void (^Something)()” mean

Question

I was trying to compile stk. During the configuration I get the error

System/Library/Frameworks/CoreAudio.framework/Headers/AudioHardware.h:162:2: error: expected identifier or '(' before '^' token (^AudioObjectPropertyListenerBlock)(

When I see the code I see ^ inside the function pointer declaration at line 162 in here. I know we can have * but what does ^ mean?

Code snippet :

#if defined(__BLOCKS__)
typedef void
(^AudioObjectPropertyListenerBlock)(    UInt32                              inNumberAddresses,
                                        const AudioObjectPropertyAddress    inAddresses[]);

Answer 1

As other answerers here say, it could be in C++/CLI.

But also, if you are on a macOS (like you hinted in one comment), this is an Objective-C block.

Its syntax is very very weird.

The block is like a C++ closures and Java anonymous inner classes, it can capture variables.

__block int insider = 0;

void(^block)() = ^{
    // print insider here using your favourite method,  printf for example
};

This is a complete NSObject (base Objective-C class), but is callable, this is not a mere function pointer.

Refer to this Apple document: https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/WorkingwithBlocks/WorkingwithBlocks.html

Now, we go to the important question, I want to run this on Linux, how ???

LLVM supports block syntax, but you should refer to this StackOverflow question for more: Clang block in Linux?

So, you should compile your code in the LLVM compiler, and use -fblocks and -lBlocksRuntime.

Don't forget to install those Linux packages:

llvm clang libblocksruntime-dev

If you are already on macOS, just use -fblocks.