ICU 76.1 76.1
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Namespaces | Typedefs | Enumerations | Functions
unumberformatter.h File Reference

C API: Localized number formatting; not recommended for C++. More...

#include "unicode/utypes.h"
#include "unicode/parseerr.h"
#include "unicode/unumberoptions.h"
#include "unicode/uformattednumber.h"

Go to the source code of this file.

Namespaces

namespace  icu
 File coll.h.
 

Typedefs

typedef enum UNumberRoundingPriority UNumberRoundingPriority
 An enum declaring how to resolve conflicts between maximum fraction digits and maximum significant digits.
 
typedef enum UNumberUnitWidth UNumberUnitWidth
 An enum declaring how to render units, including currencies.
 
typedef enum UNumberSignDisplay UNumberSignDisplay
 An enum declaring how to denote positive and negative numbers.
 
typedef enum UNumberDecimalSeparatorDisplay UNumberDecimalSeparatorDisplay
 An enum declaring how to render the decimal separator.
 
typedef enum UNumberTrailingZeroDisplay UNumberTrailingZeroDisplay
 An enum declaring how to render trailing zeros.
 
typedef struct UNumberFormatter UNumberFormatter
 C-compatible version of icu::number::LocalizedNumberFormatter.
 

Enumerations

enum  UNumberRoundingPriority { UNUM_ROUNDING_PRIORITY_RELAXED , UNUM_ROUNDING_PRIORITY_STRICT }
 An enum declaring how to resolve conflicts between maximum fraction digits and maximum significant digits. More...
 
enum  UNumberUnitWidth {
  UNUM_UNIT_WIDTH_NARROW = 0 , UNUM_UNIT_WIDTH_SHORT = 1 , UNUM_UNIT_WIDTH_FULL_NAME = 2 , UNUM_UNIT_WIDTH_ISO_CODE = 3 ,
  UNUM_UNIT_WIDTH_FORMAL = 4 , UNUM_UNIT_WIDTH_VARIANT = 5 , UNUM_UNIT_WIDTH_HIDDEN = 6 , UNUM_UNIT_WIDTH_COUNT = 7
}
 An enum declaring how to render units, including currencies. More...
 
enum  UNumberSignDisplay {
  UNUM_SIGN_AUTO , UNUM_SIGN_ALWAYS , UNUM_SIGN_NEVER , UNUM_SIGN_ACCOUNTING ,
  UNUM_SIGN_ACCOUNTING_ALWAYS , UNUM_SIGN_EXCEPT_ZERO , UNUM_SIGN_ACCOUNTING_EXCEPT_ZERO , UNUM_SIGN_NEGATIVE ,
  UNUM_SIGN_ACCOUNTING_NEGATIVE , UNUM_SIGN_COUNT = 9
}
 An enum declaring how to denote positive and negative numbers. More...
 
enum  UNumberDecimalSeparatorDisplay { UNUM_DECIMAL_SEPARATOR_AUTO , UNUM_DECIMAL_SEPARATOR_ALWAYS , UNUM_DECIMAL_SEPARATOR_COUNT }
 An enum declaring how to render the decimal separator. More...
 
enum  UNumberTrailingZeroDisplay { UNUM_TRAILING_ZERO_AUTO , UNUM_TRAILING_ZERO_HIDE_IF_WHOLE }
 An enum declaring how to render trailing zeros. More...
 

Functions

U_CAPI UNumberFormatterunumf_openForSkeletonAndLocale (const UChar *skeleton, int32_t skeletonLen, const char *locale, UErrorCode *ec)
 Creates a new UNumberFormatter for the given skeleton string and locale.
 
U_CAPI UNumberFormatterunumf_openForSkeletonAndLocaleWithError (const UChar *skeleton, int32_t skeletonLen, const char *locale, UParseError *perror, UErrorCode *ec)
 Like unumf_openForSkeletonAndLocale, but accepts a UParseError, which will be populated with the location of a skeleton syntax error if such a syntax error exists.
 
U_CAPI void unumf_formatInt (const UNumberFormatter *uformatter, int64_t value, UFormattedNumber *uresult, UErrorCode *ec)
 Uses a UNumberFormatter to format an integer to a UFormattedNumber.
 
U_CAPI void unumf_formatDouble (const UNumberFormatter *uformatter, double value, UFormattedNumber *uresult, UErrorCode *ec)
 Uses a UNumberFormatter to format a double to a UFormattedNumber.
 
U_CAPI void unumf_formatDecimal (const UNumberFormatter *uformatter, const char *value, int32_t valueLen, UFormattedNumber *uresult, UErrorCode *ec)
 Uses a UNumberFormatter to format a decimal number to a UFormattedNumber.
 
U_CAPI void unumf_close (UNumberFormatter *uformatter)
 Releases the UNumberFormatter created by unumf_openForSkeletonAndLocale().
 

Detailed Description

C API: Localized number formatting; not recommended for C++.

This is the C-compatible version of the NumberFormatter API introduced in ICU 60. C++ users should include unicode/numberformatter.h and use the proper C++ APIs.

The C API accepts a number skeleton string for specifying the settings for formatting, which covers a very large subset of all possible number formatting features. For more information on number skeleton strings, see unicode/numberformatter.h.

When using UNumberFormatter, which is treated as immutable, the results are exported to a mutable UFormattedNumber object, which you subsequently use for populating your string buffer or iterating over the fields.

Example code:

// Setup:
UErrorCode ec = U_ZERO_ERROR;
UNumberFormatter* uformatter = unumf_openForSkeletonAndLocale(u"precision-integer", -1, "en", &ec);
UFormattedNumber* uresult = unumf_openResult(&ec);
if (U_FAILURE(ec)) { return; }

// Format a double:
unumf_formatDouble(uformatter, 5142.3, uresult, &ec);
if (U_FAILURE(ec)) { return; }

// Export the string to a malloc'd buffer:
int32_t len = unumf_resultToString(uresult, NULL, 0, &ec);
// at this point, ec == U_BUFFER_OVERFLOW_ERROR
ec = U_ZERO_ERROR;
UChar* buffer = (UChar*) malloc((len+1)*sizeof(UChar));
unumf_resultToString(uresult, buffer, len+1, &ec);
if (U_FAILURE(ec)) { return; }
// buffer should equal "5,142"

// Cleanup:
unumf_close(uformatter);
unumf_closeResult(uresult);
free(buffer);

If you are a C++ user linking against the C libraries, you can use the LocalPointer versions of these APIs. The following example uses LocalPointer with the decimal number and field position APIs:

// Setup:
LocalUNumberFormatterPointer uformatter(unumf_openForSkeletonAndLocale(u"percent", -1, "en", &ec));
LocalUFormattedNumberPointer uresult(unumf_openResult(&ec));
if (U_FAILURE(ec)) { return; }

// Format a decimal number:
unumf_formatDecimal(uformatter.getAlias(), "9.87E-3", -1, uresult.getAlias(), &ec);
if (U_FAILURE(ec)) { return; }

// Get the location of the percent sign:
UFieldPosition ufpos = {UNUM_PERCENT_FIELD, 0, 0};
unumf_resultNextFieldPosition(uresult.getAlias(), &ufpos, &ec);
// ufpos should contain beginIndex=7 and endIndex=8 since the string is "0.00987%"

// No need to do any cleanup since we are using LocalPointer.

Definition in file unumberformatter.h.

Typedef Documentation

◆ UNumberDecimalSeparatorDisplay

An enum declaring how to render the decimal separator.

  • UNUM_DECIMAL_SEPARATOR_AUTO: "1", "1.1"
  • UNUM_DECIMAL_SEPARATOR_ALWAYS: "1.", "1.1"
Stable:
ICU 60

◆ UNumberFormatter

C-compatible version of icu::number::LocalizedNumberFormatter.

NOTE: This is a C-compatible API; C++ users should build against numberformatter.h instead.

Stable:
ICU 62

Definition at line 427 of file unumberformatter.h.

◆ UNumberRoundingPriority

An enum declaring how to resolve conflicts between maximum fraction digits and maximum significant digits.

There are two modes, RELAXED and STRICT:

  • RELAXED: Relax one of the two constraints (fraction digits or significant digits) in order to round the number to a higher level of precision.
  • STRICT: Enforce both constraints, resulting in the number being rounded to a lower level of precision.

The default settings for compact notation rounding are Max-Fraction = 0 (round to the nearest integer), Max-Significant = 2 (round to 2 significant digits), and priority RELAXED (choose the constraint that results in more digits being displayed).

Conflicting minimum fraction and significant digits are always resolved in the direction that results in more trailing zeros.

Example 1: Consider the number 3.141, with various different settings:

  • Max-Fraction = 1: "3.1"
  • Max-Significant = 3: "3.14"

The rounding priority determines how to resolve the conflict when both Max-Fraction and Max-Significant are set. With RELAXED, the less-strict setting (the one that causes more digits to be displayed) will be used; Max-Significant wins. With STRICT, the more-strict setting (the one that causes fewer digits to be displayed) will be used; Max-Fraction wins.

Example 2: Consider the number 8317, with various different settings:

  • Max-Fraction = 1: "8317"
  • Max-Significant = 3: "8320"

Here, RELAXED favors Max-Fraction and STRICT favors Max-Significant. Note that this larger number caused the two modes to favor the opposite result.

Stable:
ICU 69

◆ UNumberSignDisplay

An enum declaring how to denote positive and negative numbers.

Example outputs when formatting 123, 0, and -123 in en-US:

  • AUTO: "123", "0", and "-123"
  • ALWAYS: "+123", "+0", and "-123"
  • NEVER: "123", "0", and "123"
  • ACCOUNTING: "$123", "$0", and "($123)"
  • ACCOUNTING_ALWAYS: "+$123", "+$0", and "($123)"
  • EXCEPT_ZERO: "+123", "0", and "-123"
  • ACCOUNTING_EXCEPT_ZERO: "+$123", "$0", and "($123)"

The exact format, including the position and the code point of the sign, differ by locale.

Stable:
ICU 60

◆ UNumberTrailingZeroDisplay

An enum declaring how to render trailing zeros.

  • UNUM_TRAILING_ZERO_AUTO: 0.90, 1.00, 1.10
  • UNUM_TRAILING_ZERO_HIDE_IF_WHOLE: 0.90, 1, 1.10

    Stable:
    ICU 69

◆ UNumberUnitWidth

An enum declaring how to render units, including currencies.

Example outputs when formatting 123 USD and 123 meters in en-CA:

  • NARROW*: "$123.00" and "123 m"
  • SHORT: "US$ 123.00" and "123 m"
  • FULL_NAME: "123.00 US dollars" and "123 meters"
  • ISO_CODE: "USD 123.00" and undefined behavior
  • HIDDEN: "123.00" and "123"

This enum is similar to UMeasureFormatWidth.

Stable:
ICU 60

Enumeration Type Documentation

◆ UNumberDecimalSeparatorDisplay

An enum declaring how to render the decimal separator.

  • UNUM_DECIMAL_SEPARATOR_AUTO: "1", "1.1"
  • UNUM_DECIMAL_SEPARATOR_ALWAYS: "1.", "1.1"
Stable:
ICU 60
Enumerator
UNUM_DECIMAL_SEPARATOR_AUTO 

Show the decimal separator when there are one or more digits to display after the separator, and do not show it otherwise.

This is the default behavior.

Stable:
ICU 60
UNUM_DECIMAL_SEPARATOR_ALWAYS 

Always show the decimal separator, even if there are no digits to display after the separator.

Stable:
ICU 60
UNUM_DECIMAL_SEPARATOR_COUNT 

One more than the highest UNumberDecimalSeparatorDisplay value.

Internal:
Do not use. This API is for internal use only. ICU 60: The numeric value may change over time; see ICU ticket #12420.

Definition at line 369 of file unumberformatter.h.

◆ UNumberRoundingPriority

An enum declaring how to resolve conflicts between maximum fraction digits and maximum significant digits.

There are two modes, RELAXED and STRICT:

  • RELAXED: Relax one of the two constraints (fraction digits or significant digits) in order to round the number to a higher level of precision.
  • STRICT: Enforce both constraints, resulting in the number being rounded to a lower level of precision.

The default settings for compact notation rounding are Max-Fraction = 0 (round to the nearest integer), Max-Significant = 2 (round to 2 significant digits), and priority RELAXED (choose the constraint that results in more digits being displayed).

Conflicting minimum fraction and significant digits are always resolved in the direction that results in more trailing zeros.

Example 1: Consider the number 3.141, with various different settings:

  • Max-Fraction = 1: "3.1"
  • Max-Significant = 3: "3.14"

The rounding priority determines how to resolve the conflict when both Max-Fraction and Max-Significant are set. With RELAXED, the less-strict setting (the one that causes more digits to be displayed) will be used; Max-Significant wins. With STRICT, the more-strict setting (the one that causes fewer digits to be displayed) will be used; Max-Fraction wins.

Example 2: Consider the number 8317, with various different settings:

  • Max-Fraction = 1: "8317"
  • Max-Significant = 3: "8320"

Here, RELAXED favors Max-Fraction and STRICT favors Max-Significant. Note that this larger number caused the two modes to favor the opposite result.

Stable:
ICU 69
Enumerator
UNUM_ROUNDING_PRIORITY_RELAXED 

Favor greater precision by relaxing one of the rounding constraints.

Stable:
ICU 69
UNUM_ROUNDING_PRIORITY_STRICT 

Favor adherence to all rounding constraints by producing lower precision.

Stable:
ICU 69

Definition at line 118 of file unumberformatter.h.

◆ UNumberSignDisplay

An enum declaring how to denote positive and negative numbers.

Example outputs when formatting 123, 0, and -123 in en-US:

  • AUTO: "123", "0", and "-123"
  • ALWAYS: "+123", "+0", and "-123"
  • NEVER: "123", "0", and "123"
  • ACCOUNTING: "$123", "$0", and "($123)"
  • ACCOUNTING_ALWAYS: "+$123", "+$0", and "($123)"
  • EXCEPT_ZERO: "+123", "0", and "-123"
  • ACCOUNTING_EXCEPT_ZERO: "+$123", "$0", and "($123)"

The exact format, including the position and the code point of the sign, differ by locale.

Stable:
ICU 60
Enumerator
UNUM_SIGN_AUTO 

Show the minus sign on negative numbers, and do not show the sign on positive numbers.

This is the default behavior.

If using this option, a sign will be displayed on negative zero, including negative numbers that round to zero. To hide the sign on negative zero, use the NEGATIVE option.

Stable:
ICU 60
UNUM_SIGN_ALWAYS 

Show the minus sign on negative numbers and the plus sign on positive numbers, including zero.

To hide the sign on zero, see UNUM_SIGN_EXCEPT_ZERO.

Stable:
ICU 60
UNUM_SIGN_NEVER 

Do not show the sign on positive or negative numbers.

Stable:
ICU 60
UNUM_SIGN_ACCOUNTING 

Use the locale-dependent accounting format on negative numbers, and do not show the sign on positive numbers.

The accounting format is defined in CLDR and varies by locale; in many Western locales, the format is a pair of parentheses around the number.

Note: Since CLDR defines the accounting format in the monetary context only, this option falls back to the AUTO sign display strategy when formatting without a currency unit. This limitation may be lifted in the future.

Stable:
ICU 60
UNUM_SIGN_ACCOUNTING_ALWAYS 

Use the locale-dependent accounting format on negative numbers, and show the plus sign on positive numbers, including zero.

For more information on the accounting format, see the ACCOUNTING sign display strategy. To hide the sign on zero, see UNUM_SIGN_ACCOUNTING_EXCEPT_ZERO.

Stable:
ICU 60
UNUM_SIGN_EXCEPT_ZERO 

Show the minus sign on negative numbers and the plus sign on positive numbers.

Do not show a sign on zero, numbers that round to zero, or NaN.

Stable:
ICU 61
UNUM_SIGN_ACCOUNTING_EXCEPT_ZERO 

Use the locale-dependent accounting format on negative numbers, and show the plus sign on positive numbers.

Do not show a sign on zero, numbers that round to zero, or NaN. For more information on the accounting format, see the ACCOUNTING sign display strategy.

Stable:
ICU 61
UNUM_SIGN_NEGATIVE 

Same as AUTO, but do not show the sign on negative zero.

Stable:
ICU 69
UNUM_SIGN_ACCOUNTING_NEGATIVE 

Same as ACCOUNTING, but do not show the sign on negative zero.

Stable:
ICU 69
UNUM_SIGN_COUNT 

One more than the highest UNumberSignDisplay value.

Internal:
Do not use. This API is for internal use only. ICU 60: The numeric value may change over time; see ICU ticket #12420.

Definition at line 264 of file unumberformatter.h.

◆ UNumberTrailingZeroDisplay

An enum declaring how to render trailing zeros.

  • UNUM_TRAILING_ZERO_AUTO: 0.90, 1.00, 1.10
  • UNUM_TRAILING_ZERO_HIDE_IF_WHOLE: 0.90, 1, 1.10

    Stable:
    ICU 69
Enumerator
UNUM_TRAILING_ZERO_AUTO 

Display trailing zeros according to the settings for minimum fraction and significant digits.

Stable:
ICU 69
UNUM_TRAILING_ZERO_HIDE_IF_WHOLE 

Same as AUTO, but hide trailing zeros after the decimal separator if they are all zero.

Stable:
ICU 69

Definition at line 403 of file unumberformatter.h.

◆ UNumberUnitWidth

An enum declaring how to render units, including currencies.

Example outputs when formatting 123 USD and 123 meters in en-CA:

  • NARROW*: "$123.00" and "123 m"
  • SHORT: "US$ 123.00" and "123 m"
  • FULL_NAME: "123.00 US dollars" and "123 meters"
  • ISO_CODE: "USD 123.00" and undefined behavior
  • HIDDEN: "123.00" and "123"

This enum is similar to UMeasureFormatWidth.

Stable:
ICU 60
Enumerator
UNUM_UNIT_WIDTH_NARROW 

Print an abbreviated version of the unit name.

Similar to SHORT, but always use the shortest available abbreviation or symbol. This option can be used when the context hints at the identity of the unit. For more information on the difference between NARROW and SHORT, see SHORT.

In CLDR, this option corresponds to the "Narrow" format for measure units and the "¤¤¤¤¤" placeholder for currencies.

Stable:
ICU 60
UNUM_UNIT_WIDTH_SHORT 

Print an abbreviated version of the unit name.

Similar to NARROW, but use a slightly wider abbreviation or symbol when there may be ambiguity. This is the default behavior.

For example, in es-US, the SHORT form for Fahrenheit is "{0} °F", but the NARROW form is "{0}°", since Fahrenheit is the customary unit for temperature in that locale.

In CLDR, this option corresponds to the "Short" format for measure units and the "¤" placeholder for currencies.

Stable:
ICU 60
UNUM_UNIT_WIDTH_FULL_NAME 

Print the full name of the unit, without any abbreviations.

In CLDR, this option corresponds to the default format for measure units and the "¤¤¤" placeholder for currencies.

Stable:
ICU 60
UNUM_UNIT_WIDTH_ISO_CODE 

Use the three-digit ISO XXX code in place of the symbol for displaying currencies.

The behavior of this option is currently undefined for use with measure units.

In CLDR, this option corresponds to the "¤¤" placeholder for currencies.

Stable:
ICU 60
UNUM_UNIT_WIDTH_FORMAL 

Use the formal variant of the currency symbol; for example, "NT$" for the New Taiwan dollar in zh-TW.

Behavior of this option with non-currency units is not defined at this time.

Stable:
ICU 68
UNUM_UNIT_WIDTH_VARIANT 

Use the alternate variant of the currency symbol; for example, "TL" for the Turkish lira (TRY).

Behavior of this option with non-currency units is not defined at this time.

Stable:
ICU 68
UNUM_UNIT_WIDTH_HIDDEN 

Format the number according to the specified unit, but do not display the unit.

For currencies, apply monetary symbols and formats as with SHORT, but omit the currency symbol. For measure units, the behavior is equivalent to not specifying the unit at all.

Stable:
ICU 60
UNUM_UNIT_WIDTH_COUNT 

One more than the highest UNumberUnitWidth value.

Internal:
Do not use. This API is for internal use only. ICU 60: The numeric value may change over time; see ICU ticket #12420.

Definition at line 152 of file unumberformatter.h.

Function Documentation

◆ unumf_close()

U_CAPI void unumf_close ( UNumberFormatter uformatter)

Releases the UNumberFormatter created by unumf_openForSkeletonAndLocale().

Parameters
uformatterAn object created by unumf_openForSkeletonAndLocale().
Stable:
ICU 62

◆ unumf_formatDecimal()

U_CAPI void unumf_formatDecimal ( const UNumberFormatter uformatter,
const char *  value,
int32_t  valueLen,
UFormattedNumber uresult,
UErrorCode ec 
)

Uses a UNumberFormatter to format a decimal number to a UFormattedNumber.

A string, field position, and other information can be retrieved from the UFormattedNumber.

The UNumberFormatter can be shared between threads. Each thread should have its own local UFormattedNumber, however, for storing the result of the formatting operation.

The syntax of the unformatted number is a "numeric string" as defined in the Decimal Arithmetic Specification, available at http://speleotrove.com/decimal

NOTE: This is a C-compatible API; C++ users should build against numberformatter.h instead.

Parameters
uformatterA formatter object created by unumf_openForSkeletonAndLocale or similar.
valueThe numeric string to be formatted.
valueLenThe length of the numeric string, or -1 if it is NUL-terminated.
uresultThe object that will be mutated to store the result; see unumf_openResult.
ecSet if an error occurs.
Stable:
ICU 62

◆ unumf_formatDouble()

U_CAPI void unumf_formatDouble ( const UNumberFormatter uformatter,
double  value,
UFormattedNumber uresult,
UErrorCode ec 
)

Uses a UNumberFormatter to format a double to a UFormattedNumber.

A string, field position, and other information can be retrieved from the UFormattedNumber.

The UNumberFormatter can be shared between threads. Each thread should have its own local UFormattedNumber, however, for storing the result of the formatting operation.

NOTE: This is a C-compatible API; C++ users should build against numberformatter.h instead.

Parameters
uformatterA formatter object created by unumf_openForSkeletonAndLocale or similar.
valueThe number to be formatted.
uresultThe object that will be mutated to store the result; see unumf_openResult.
ecSet if an error occurs.
Stable:
ICU 62

◆ unumf_formatInt()

U_CAPI void unumf_formatInt ( const UNumberFormatter uformatter,
int64_t  value,
UFormattedNumber uresult,
UErrorCode ec 
)

Uses a UNumberFormatter to format an integer to a UFormattedNumber.

A string, field position, and other information can be retrieved from the UFormattedNumber.

The UNumberFormatter can be shared between threads. Each thread should have its own local UFormattedNumber, however, for storing the result of the formatting operation.

NOTE: This is a C-compatible API; C++ users should build against numberformatter.h instead.

Parameters
uformatterA formatter object created by unumf_openForSkeletonAndLocale or similar.
valueThe number to be formatted.
uresultThe object that will be mutated to store the result; see unumf_openResult.
ecSet if an error occurs.
Stable:
ICU 62

◆ unumf_openForSkeletonAndLocale()

U_CAPI UNumberFormatter * unumf_openForSkeletonAndLocale ( const UChar skeleton,
int32_t  skeletonLen,
const char *  locale,
UErrorCode ec 
)

Creates a new UNumberFormatter for the given skeleton string and locale.

This is currently the only method for creating a new UNumberFormatter.

Objects of type UNumberFormatter returned by this method are threadsafe.

For more details on skeleton strings, see the documentation in numberformatter.h. For more details on the usage of this API, see the documentation at the top of unumberformatter.h.

For more information on number skeleton strings, see: https://unicode-org.github.io/icu/userguide/format_parse/numbers/skeletons.html

NOTE: This is a C-compatible API; C++ users should build against numberformatter.h instead.

Parameters
skeletonThe skeleton string, like u"percent precision-integer"
skeletonLenThe number of UChars in the skeleton string, or -1 if it is NUL-terminated.
localeThe NUL-terminated locale ID.
ecSet if an error occurs.
Stable:
ICU 62

◆ unumf_openForSkeletonAndLocaleWithError()

U_CAPI UNumberFormatter * unumf_openForSkeletonAndLocaleWithError ( const UChar skeleton,
int32_t  skeletonLen,
const char *  locale,
UParseError perror,
UErrorCode ec 
)

Like unumf_openForSkeletonAndLocale, but accepts a UParseError, which will be populated with the location of a skeleton syntax error if such a syntax error exists.

For more information on number skeleton strings, see: https://unicode-org.github.io/icu/userguide/format_parse/numbers/skeletons.html

Parameters
skeletonThe skeleton string, like u"percent precision-integer"
skeletonLenThe number of UChars in the skeleton string, or -1 if it is NUL-terminated.
localeThe NUL-terminated locale ID.
perrorA parse error struct populated if an error occurs when parsing. Can be NULL. If no error occurs, perror->offset will be set to -1.
ecSet if an error occurs.
Stable:
ICU 64