Question

I'm writing a program in C for OS X (for the terminal). As mentioned in the title, just need the id and/or name of the application receiving the keystrokes i.e. the focused window.

I've found the you can use frontmostApplication but I can't use it in C or can't figure out how to do it. I'm new to writing stuff in macOS, any help much appreciated.

Answer 1

The UI layer on macOS is all written in Objective-C, which you can't easily call from straight C code (well, technically, you could use objc_msgSend(), but trust me, you don't want to do that). Fortunately, the amount of Objective-C code you'll need to do this is quite small, and you can separate it out into a separate file which you include from your C code:

GetFrontApplication.h:

#ifndef GETFRONTAPPLICATION_H
#define GETFRONTAPPLICATION_H

char *GetFrontmostApplication(void);

#endif /* GETFRONTAPPLICATION_H */

GetFrontApplication.m:

@import Cocoa;

char *GetFrontmostApplication(void) {
    @autoreleasepool {
        NSRunningApplication *frontApp = [[NSWorkspace sharedWorkspace] frontmostApplication];

        return strdup(frontApp.localizedName.UTF8String);
    }
}

Now you can just #include "GetFrontApplication.h" and call GetFrontmostApplication() from your C code, and you'll get a char * containing the name of the application. Make sure to free() the string after you're done with it.

How to get the id of the application receiving key strokes in C for macos?

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