Format Date and Time Examples

Overview

The ICU DateFormat interface enables you to format a date in milliseconds into a string representation of the date. Also, the interface enables you to parse the string back to the internal date representation in milliseconds.

C++

DateFormat* df = DateFormat::createDateInstance();
UnicodeString myString;
UDate myDateArr[] = { 0.0, 100000000.0, 2000000000.0 }; 
for (int32_t i = 0; i < 3; ++i) {
  myString.remove();
  cout << df->format( myDateArr[i], myString ) << endl;
}

/* 1st example: format the dates in millis 100000000 and
2000000000 */
UErrorCode status=U_ZERO_ERROR;
int32_t i, myStrlen=0;
UChar* myString;
UDate myDateArr[] = { 0.0, 100000000.0, 2000000000.0 }; // test values
UDateFormat* df = udat_open(UCAL_DEFAULT, UCAL_DEFAULT, NULL, "GMT", &status);
for (i = 0; i < 3; ++i) {
  myStrlen = udat_format(df, myDateArr[i], NULL, myStrlen, NULL, &status);
  if(status==U_BUFFER_OVERFLOW_ERROR){
    status=U_ZERO_ERROR;
    myString=(UChar*)malloc(sizeof(UChar) * (myStrlen+1) );
    udat_format(df, myDateArr[i], myString, myStrlen+1, NULL, &status);
    printf("%s\n", austrdup(myString) ); 
    /* austrdup( a function used to convert UChar* to char*) */
    free(myString);
  }
}

To parse a date for a different locale, specify it in the locale call. This call creates a formatting object.

C++

DateFormat* df = DateFormat::createDateInstance
  ( DateFormat::SHORT, Locale::getFrance());

/* 2nd example: parse a date with short French date/time
formatter */
UDateFormat* df = udat_open(UDAT_SHORT, UDAT_SHORT, "fr_FR", "GMT", &status);
UErrorCode status = U_ZERO_ERROR;
int32_t parsepos=0;     
UDate myDate = udat_parse(df, myString, u_strlen(myString), &parsepos,
&status);

To get specific fields of a date, you can use the FieldPosition function for C++ or UFieldPosition function for C.

C++

UErrorCode status = U_ZERO_ERROR;
FieldPosition pos(DateFormat::YEAR_FIELD)
UDate myDate = Calendar::getNow();
UnicodeString str;
DateFormat* df = DateFormat::createDateInstance
  ( DateFormat::LONG, Locale::getFrance());

df->format(myDate, str, pos, status);
cout << pos.getBeginIndex() << "," << pos. getEndIndex() << endl;

UErrorCode status = U_ZERO_ERROR;
  UFieldPosition pos;
  UChar *myString;
  int32_t myStrlen = 0;
  char buffer[1024];


  pos.field = 1; /* Same as the DateFormat::EField enum */
  UDateFormat* dfmt = udat_open(UCAL_DEFAULT, UCAL_DEFAULT, NULL, "PST",
&status);
  myStrlen = udat_format(dfmt, myDate, NULL, myStrlen, &pos, &status);
  if (status==U_BUFFER_OVERFLOW_ERROR){
      status=U_ZERO_ERROR;
      myString=(UChar*)malloc(sizeof(UChar) * (myStrlen+1) );
      udat_format(dfmt, myDate, myString, myStrlen+1, &pos, &status);
  }
  printf("date format: %s\n", u_austrcpy(buffer, myString));
  buffer[pos.endIndex] = 0;   // NULL terminate the string.
  printf("UFieldPosition position equals %s\n", &buffer[pos.beginIndex]);

DateTimePatternGenerator

This class lets you get a different variety of patterns, such as month+day. The following illustrates this in Java.

        // set up the generator
        DateTimePatternGenerator generator
          = DateTimePatternGenerator.getInstance(locale);
        
        // get a pattern for an abbreviated month and day
        final String pattern = generator.getBestPattern("MMMd");
        SimpleDateFormat formatter = new SimpleDateFormat(pattern, locale);
        
        // use it to format (or parse)
        String formatted = formatter.format(new Date());
        // for French, the result is "13 sept."

It also contains some helper functions for parsing patterns. Here's an example of replacing the kind of timezone used in a pattern.

    /**
     * Replace the zone string with a different type, eg v's for z's, etc.
     * <p>Called with a pattern, such as one gotten from 
     * <pre>
     * String pattern = ((SimpleDateFormat)
     * DateFormat.getTimeInstance(style, locale)).toPattern();
     * </pre>
     * @param pattern original pattern to change, such as "HH:mm zzzz"
     * @param newZone Must be: z, zzzz, Z, ZZZZ, v, vvvv, V, or VVVV
     * @return
     */
    public String replaceZoneString(String pattern, String newZone) {
        final List itemList = formatParser.set(pattern).getItems();
        boolean found = false;
        for (int i = 0; i < itemList.size(); ++i) {
            Object item = itemList.get(i);
            if (item instanceof VariableField) {
                // the first character of the variable field determines the type,
                // according to CLDR.
                String variableField = item.toString();
                switch (variableField.charAt(0)) {
                case 'z': case 'Z': case 'v': case 'V':
                    if (!variableField.equals(newZone)) {
                        found = true;
                        itemList.set(i, new VariableField(newZone));
                    }
                    break;
                }
            }
        }
        return found ? formatParser.toString() : pattern;
    }

User Guide for ICU v3.8 Generated 2007-09-14.