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Using Dates

This task contains examples on creating, comparing, and converting dates. Listing 1 shows you how to get the current absolute time and convert it into a CFDate object.

Listing 1 Creating a CFDate object

CFAbsoluteTime      absTime;

CFDateRef           aCFDate;

absTime = CFAbsoluteTimeGetCurrent();

aCFDate = CFDateCreate(kCFAllocatorDefault, absTime);

To compare two dates, use the compare function CFDateCompare as shown in Listing 2.

Listing 2 Comparing two CFDate objects

// Standard Core Foundation comparison result.

CFComparisonResult result;

// Create two CFDates from absolute time.

date1 = CFDateCreate(kCFAllocatorDefault, CFAbsoluteTimeGetCurrent());

date2 = CFDateCreate(kCFAllocatorDefault, CFAbsoluteTimeGetCurrent());

// Pass NULL for the context param.

result = CFDateCompare(date1, date2, NULL);

switch (result) {

    case kCFCompareLessThan:

        printf("date1 is before date2!\n");

        break;

    case kCFCompareEqualTo:

        printf("date1 is the same as date2!\n");

        break;

    case kCFCompareGreaterThan:

        printf("date1 is after date2!\n");

        break;

The CFDateCompare function performs exact comparisons, which means it detects sub-second differences between dates. You might want to compare dates with a less fine granularity. For example, you might want to consider two dates equal if they are within one minute of each other. This can be accomplished by simply converting the CFDates to absolute time and comparing the two floating-point values using your fuzziness factor. To compare Gregorian units like month or week, you can convert both CFDates to CFGregorianDate and compare the appropriate fields. Converting absolute time to and from Gregorian dates is quite simple. Listing 3 demonstrates how to do this.

Listing 3 Working with Gregorian dates

Boolean             status;

CFGregorianDate     gregDate;

CFAbsoluteTime      absTime;

// Construct a Gregorian date.

gregDate.year = 1999;

gregDate.month = 11;

gregDate.day = 23;

gregDate.hour = 17;

gregDate.minute = 33;

gregDate.second = 22.7;

// Check the validity of the date.

status = CFGregorianDateIsValid(gregDate, kCFGregorianAllUnits);

printf("Is my Gregorian date valid? %d\n", status);

// Convert the Gregorian date to absolute time.

absTime = CFGregorianDateGetAbsoluteTime(gregDate, NULL);

printf("The Absolute Time from a Gregorian date is: %d\n", absTime);

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