_CFPreferencesCopyApplicationMap example

app_map.c

/* re-implementation of the behaviour that the /usr/bin/defaults application
 * uses to read sandboxed preference data */

#include <CoreFoundation/CoreFoundation.h>

#define EX_BUNDLE_ID "com.apple.mail"
#define EX_KEY "JunkMailBehavior"

// undocumented, internal CFPreferences API call
extern CFDictionaryRef _CFPreferencesCopyApplicationMap(CFStringRef userName, CFStringRef hostName);

int main()
{
	CFPropertyListRef app_map;
	CFArrayRef bundle_urls;
	CFURLRef current_url;
	CFStringRef path;
	CFMutableStringRef plist_path;
	CFPropertyListRef value;

	app_map = _CFPreferencesCopyApplicationMap(kCFPreferencesCurrentUser, kCFPreferencesAnyHost);

	if (app_map == NULL)
	{
		printf("problem getting ApplicationMap\n");
		return -1;
	}

	if (true != CFDictionaryGetValueIfPresent(app_map, CFSTR(EX_BUNDLE_ID), (const void**)&bundle_urls))
	{
		printf("no matching bundle ID found in ApplicationMap: %s\n", EX_BUNDLE_ID);
		return -2;
	}

	if (CFArrayGetCount(bundle_urls) < 1)
	{
		printf("no URLs returned by ApplicationMap for given bundle ID\n");
		return -3;
	}

	/* the dictionary returned by _CFPreferencesCopyApplicationMap is keyed
	 * by bundle id and contains an array CFURLs. it's listed by (all) 
	 * sandbox locations first, then typical ~/Library/Preferences. for this
	 * example only take the first (possibly sandboxed) location */
	current_url = CFArrayGetValueAtIndex(bundle_urls, 0);
	path = CFURLCopyPath(current_url);

	// create and assemble our plist path
	plist_path = CFStringCreateMutable(kCFAllocatorDefault, 0);
	CFStringAppend(plist_path, path);
	CFStringAppend(plist_path, CFSTR(EX_BUNDLE_ID));

	value = CFPreferencesCopyValue(CFSTR(EX_KEY), plist_path, kCFPreferencesCurrentUser, kCFPreferencesAnyUser);

	printf("result of CFPreferencesCopyValue on %s of %s via ApplicationMap at path:\n", EX_KEY, EX_BUNDLE_ID);

	CFShow(plist_path);
	CFShow(value);

	CFRelease(value);
	CFRelease(plist_path);
	CFRelease(path);
	CFRelease(app_map);

	return 0;
}

See also this tweet. It talks about _CFPreferences*WithContainer().