Documentation

FieldPosition is a simple class used by Format and its subclasses to identify fields in formatted output. Fields are identified by constants, whose names typically end with _FIELD, defined in the various subclasses of Format. See ERA_FIELD and its friends in DateFormat for an example.

FieldPosition keeps track of the position of the field within the formatted output with two indices: the index of the first character of the field and the index of the last character of the field.

One version of the format method in the various Format classes requires a FieldPosition object as an argument. You use this format method to perform partial formatting or to get information about the formatted output (such as the position of a field).

Below is an example of using FieldPosition to aid alignment of an array of formatted floating-point numbers on their decimal points:

.      double doubleNum[] = {123456789.0, -12345678.9, 1234567.89, -123456.789,
.                 12345.6789, -1234.56789, 123.456789, -12.3456789, 1.23456789};
.      int dNumSize = (int)(sizeof(doubleNum)/sizeof(double));
.      
.      UErrorCode status = U_ZERO_ERROR;
.      DecimalFormat* fmt = (DecimalFormat*) NumberFormat::createInstance(status);
.      fmt->setDecimalSeparatorAlwaysShown(true);
.      
.      const int tempLen = 20;
.      char temp[tempLen];
.      
.      for (int i=0; i<dNumSize; i++) {
.          FieldPosition pos(NumberFormat::INTEGER_FIELD);
.          UnicodeString buf;
.          char fmtText[tempLen];
.          ToCharString(fmt->format(doubleNum[i], buf, pos), fmtText);
.          for (int j=0; j<tempLen; j++) temp[j] = ' '; // clear with spaces
.          temp[__min(tempLen, tempLen-pos.getEndIndex())] = '\0';
.          cout << temp << fmtText   << endl;
.      }
.      delete fmt;

The code will generate the following output:

.          123,456,789.000
.          -12,345,678.900
.            1,234,567.880
.             -123,456.789
.               12,345.678
.               -1,234.567
.                  123.456
.                  -12.345
.                    1.234

This class has no child classes.