PreferencesExample.c

/*
     File: PreferencesExample.c
 Abstract: Simple CFPreferences example program; reads/writes a preference.
  Version: 1.1
 
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 */
 
#include <CoreFoundation/CoreFoundation.h>
#include <stdio.h>
#include <stdlib.h>
 
 
// This function will print the provided arguments (printf style varargs) out to the console.
// Note that the CFString formatting function accepts "%@" as a way to display CF types.
// For types other than CFString and CFNumber, the result of %@ is mostly for debugging
// and can differ between releases and different platforms.
 
void show(CFStringRef formatString, ...) {
    CFStringRef resultString;
    CFDataRef data;
    va_list argList;
 
    va_start(argList, formatString);
    resultString = CFStringCreateWithFormatAndArguments(NULL, NULL, formatString, argList);
    va_end(argList);
 
    data = CFStringCreateExternalRepresentation(NULL, resultString, CFStringGetSystemEncoding(), '?');
 
    if (data != NULL) {
        printf ("%.*s\n\n", (int)CFDataGetLength(data), CFDataGetBytePtr(data));
        CFRelease(data);
    }
       
    CFRelease(resultString);
}
 
 
/* Read old high score, which is saved as a CFNumber under the key "High Score"; bump it up and save it.
*/
void simplePreferencesExample(void) {
    
    CFStringRef appName = CFSTR("A Game");
    CFStringRef highScoreKey = CFSTR("High Score");
    CFNumberRef value;
    int highScore;
 
    // First retrieve the previous value...
 
    // CFPreferencesCopyAppValue() and CFPreferencesSetAppValue() are the most straightforward way
    // for an app to read/write preferences that are per user and per app; they will apply on all 
    // machines (on which this user can log in, of course --- for users who are local to a machine,
    // the preferences will end up being restricted to that host). These functions also do a search 
    // through the various cases; if a preference has been set in a less-specific domain (for 
    // instance, "all apps"), its value will be retrieved with this call. This allows globally 
    // setting some preference values (which makes more sense for some preferences than others).
 
    // Note that you can read/write any "property list" type in preferences; these are
    // CFArray, CFDictionary, CFNumber, CFBoolean, CFData, and CFString.
    // This example just shows CFNumber.
 
    value = CFPreferencesCopyAppValue(highScoreKey, appName);   
 
    if (value) {
    // Numbers come out of preferences as CFNumbers.
    if (!CFNumberGetValue(value, kCFNumberIntType, &highScore)) highScore = 0;
    CFRelease(value);
 
    show(CFSTR("The old high score was %d."), highScore);
    } else {
    // No previous value
    show(CFSTR("There is no old high score."));
    highScore = 0;
    }
 
    highScore += 5;
 
    show(CFSTR("Recording new high score, %d"), highScore);
 
    value = CFNumberCreate(NULL, kCFNumberIntType, &highScore); 
 
    CFPreferencesSetAppValue(highScoreKey, value, appName);
 
    CFRelease(value);
 
    // Without an explicit synchronize, the saved values actually do not get written out.
    // If you are writing multiple preferences, you might want to sync only after the last one.
    // A preference panel might want to synchronize when the user hits "OK".
    // In some cases you might not want to sync at all until the app quits.
    // The AppKit automatically synchronizes on app termination, so Cocoa apps don't need to do this.
 
    (void)CFPreferencesAppSynchronize(appName);
}
 
 
int main (int argc, const char *argv[]) {
    simplePreferencesExample();
    
    return 0;
}