Base class for all formats.
This is an abstract base class which specifies the protocol for classes which convert other objects or values, such as numeric values and dates, and their string representations. In some cases these representations may be localized or contain localized characters or strings. For example, a numeric formatter such as DecimalFormat may convert a numeric value such as 12345 to the string "$12,345". It may also parse the string back into a numeric value. A date and time formatter like SimpleDateFormat may represent a specific date, encoded numerically, as a string such as "Wednesday, February 26, 1997 AD".
Many of the concrete subclasses of Format employ the notion of a pattern. A pattern is a string representation of the rules which govern the interconversion between values and strings. For example, a DecimalFormat object may be associated with the pattern "$#,##0.00;($#,##0.00)", which is a common US English format for currency values, yielding strings such as "$1,234.45" for 1234.45, and "($987.65)" for 987.6543. The specific syntax of a pattern is defined by each subclass.
Even though many subclasses use patterns, the notion of a pattern is not inherent to Format classes in general, and is not part of the explicit base class protocol.
Two complex formatting classes bear mentioning. These are MessageFormat and ChoiceFormat. ChoiceFormat is a subclass of NumberFormat which allows the user to format different number ranges as strings. For instance, 0 may be represented as "no files", 1 as "one file", and any number greater than 1 as "many files". MessageFormat is a formatter which utilizes other Format objects to format a string containing with multiple values. For instance, A MessageFormat object might produce the string "There are no files on the disk MyDisk on February 27, 1997." given the arguments 0, "MyDisk", and the date value of 2/27/97. See the ChoiceFormat and MessageFormat headers for further information.
If formatting is unsuccessful, a failing UErrorCode is returned when the Format cannot format the type of object, otherwise if there is something illformed about the the Unicode replacement character 0xFFFD is returned.
If there is no match when parsing, a parse failure UErrorCode is returned for methods which take no ParsePosition. For the method that takes a ParsePosition, the index parameter is left unchanged.
User subclasses are not supported. While clients may write subclasses, such code will not necessarily work and will not be guaranteed to work stably from release to release.
Definition at line 99 of file format.h.
Parse a string to produce an object.
This is a pure virtual method which subclasses must implement. This method allows polymorphic parsing of strings into Formattable objects.
Before calling, set parse_pos.index to the offset you want to start parsing at in the source. After calling, parse_pos.index is the end of the text you parsed. If error occurs, index is unchanged.
When parsing, leading whitespace is discarded (with successful parse), while trailing whitespace is left as is.
Example:
Parsing "_12_xy" (where _ represents a space) for a number, with index == 0 will result in the number 12, with parse_pos.index updated to 3 (just before the second space). Parsing a second time will result in a failing UErrorCode since "xy" is not a number, and leave index at 3.
Subclasses will typically supply specific parse methods that return different types of values. Since methods can't overload on return types, these will typically be named "parse", while this polymorphic method will always be called parseObject. Any parse method that does not take a parse_pos should set status to an error value when no text in the required format is at the start position.
Implemented in icu::TimeUnitFormat, icu::MessageFormat, icu::TimeZoneFormat, icu::SelectFormat, icu::PluralFormat, icu::NumberFormat, icu::DateIntervalFormat, icu::DateFormat, and icu::MeasureFormat.
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