ICU 74.2: common/unicode/utf.h File Reference

ICU 74.2 74.2

Macros
utf.h File Reference

C API: Code point macros. More...

`#include "unicode/umachine.h"`
`#include "unicode/utf8.h"`
`#include "unicode/utf16.h"`
`#include "unicode/utf_old.h"`

Go to the source code of this file.

## Macros
#define | U_IS_UNICODE_NONCHAR(c)
| Is this code point a Unicode noncharacter?
#define | U_IS_UNICODE_CHAR(c)
| Is c a Unicode code point value (0..U+10ffff) that can be assigned a character?
#define | U_IS_BMP(c) ((uint32_t)(c)<=0xffff)
| Is this code point a BMP code point (U+0000..U+ffff)?
#define | U_IS_SUPPLEMENTARY(c) ((uint32_t)((c)-0x10000)<=0xfffff)
| Is this code point a supplementary code point (U+10000..U+10ffff)?
#define | U_IS_LEAD(c) (((c)&0xfffffc00)==0xd800)
| Is this code point a lead surrogate (U+d800..U+dbff)?
#define | U_IS_TRAIL(c) (((c)&0xfffffc00)==0xdc00)
| Is this code point a trail surrogate (U+dc00..U+dfff)?
#define | U_IS_SURROGATE(c) (((c)&0xfffff800)==0xd800)
| Is this code point a surrogate (U+d800..U+dfff)?
#define | U_IS_SURROGATE_LEAD(c) (((c)&0x400)==0)
| Assuming c is a surrogate code point (U_IS_SURROGATE(c)), is it a lead surrogate?
#define | U_IS_SURROGATE_TRAIL(c) (((c)&0x400)!=0)
| Assuming c is a surrogate code point (U_IS_SURROGATE(c)), is it a trail surrogate?

## Detailed Description

C API: Code point macros.

This file defines macros for checking whether a code point is a surrogate or a non-character etc.

If U_NO_DEFAULT_INCLUDE_UTF_HEADERS is 0 then utf.h is included by utypes.h and itself includes utf8.h and utf16.h after some common definitions. If U_NO_DEFAULT_INCLUDE_UTF_HEADERS is 1 then each of these headers must be included explicitly if their definitions are used.

utf8.h and utf16.h define macros for efficiently getting code points in and out of UTF-8/16 strings. utf16.h macros have "U16_" prefixes. utf8.h defines similar macros with "U8_" prefixes for UTF-8 string handling.

ICU mostly processes 16-bit Unicode strings. Most of the time, such strings are well-formed UTF-16. Single, unpaired surrogates must be handled as well, and are treated in ICU like regular code points where possible. (Pairs of surrogate code points are indistinguishable from supplementary code points encoded as pairs of supplementary code units.)

In fact, almost all Unicode code points in normal text (>99%) are on the BMP (<=U+ffff) and even <=U+d7ff. ICU functions handle supplementary code points (U+10000..U+10ffff) but are optimized for the much more frequently occurring BMP code points.

umachine.h defines UChar to be an unsigned 16-bit integer. Since ICU 59, ICU uses char16_t in C++, UChar only in C, and defines UChar=char16_t by default. See the UChar API docs for details.

UChar32 is defined to be a signed 32-bit integer (int32_t), large enough for a 21-bit Unicode code point (Unicode scalar value, 0..0x10ffff) and U_SENTINEL (-1). Before ICU 2.4, the definition of UChar32 was similarly platform-dependent as the definition of UChar. For details see the documentation for UChar32 itself.

utf.h defines a small number of C macros for single Unicode code points. These are simple checks for surrogates and non-characters. For actual Unicode character properties see uchar.h.

By default, string operations must be done with error checking in case a string is not well-formed UTF-16 or UTF-8.

The U16_ macros detect if a surrogate code unit is unpaired (lead unit without trail unit or vice versa) and just return the unit itself as the code point.

The U8_ macros detect illegal byte sequences and return a negative value. Starting with ICU 60, the observable length of a single illegal byte sequence skipped by one of these macros follows the Unicode 6+ recommendation which is consistent with the W3C Encoding Standard.

There are ..._OR_FFFD versions of both U16_ and U8_ macros that return U+FFFD for illegal code unit sequences.

The regular "safe" macros require that the initial, passed-in string index is within bounds. They only check the index when they read more than one code unit. This is usually done with code similar to the following loop:

    while(i<length) {
      U16_NEXT(s, i, length, c);
      // use c
    }

When it is safe to assume that text is well-formed UTF-16 (does not contain single, unpaired surrogates), then one can use U16_..._UNSAFE macros. These do not check for proper code unit sequences or truncated text and may yield wrong results or even cause a crash if they are used with "malformed" text. In practice, U16_..._UNSAFE macros will produce slightly less code but should not be faster because the processing is only different when a surrogate code unit is detected, which will be rare.

Similarly for UTF-8, there are "safe" macros without a suffix, and U8_..._UNSAFE versions. The performance differences are much larger here because UTF-8 provides so many opportunities for malformed sequences. The unsafe UTF-8 macros are entirely implemented inside the macro definitions and are fast, while the safe UTF-8 macros call functions for some complicated cases.

Unlike with UTF-16, malformed sequences cannot be expressed with distinct code point values (0..U+10ffff). They are indicated with negative values instead.

For more information see the ICU User Guide Strings chapter (https://unicode-org.github.io/icu/userguide/strings).

Usage: ICU coding guidelines for if() statements should be followed when using these macros. Compound statements (curly braces {}) must be used for if-else-while... bodies and all macro statements should be terminated with semicolon.

Stable:
  ICU 2.4

Definition in file utf.h.

## Macro Definition Documentation

## ◆ U_IS_BMP

#define U_IS_BMP | ( |  | c | ) | ((uint32_t)(c)<=0xffff)

Is this code point a BMP code point (U+0000..U+ffff)?

Parameters

  c | 32-bit code point

Returns
  true or false

Stable:
  ICU 2.8

Definition at line 161 of file utf.h.

## ◆ U_IS_LEAD

#define U_IS_LEAD | ( |  | c | ) | (((c)&0xfffffc00)==0xd800)

Is this code point a lead surrogate (U+d800..U+dbff)?

Parameters

  c | 32-bit code point

Returns
  true or false

Stable:
  ICU 2.4

Definition at line 177 of file utf.h.

## ◆ U_IS_SUPPLEMENTARY

#define U_IS_SUPPLEMENTARY | ( |  | c | ) | ((uint32_t)((c)-0x10000)<=0xfffff)

Is this code point a supplementary code point (U+10000..U+10ffff)?

Parameters

  c | 32-bit code point

Returns
  true or false

Stable:
  ICU 2.8

Definition at line 169 of file utf.h.

## ◆ U_IS_SURROGATE

#define U_IS_SURROGATE | ( |  | c | ) | (((c)&0xfffff800)==0xd800)

Is this code point a surrogate (U+d800..U+dfff)?

Parameters

  c | 32-bit code point

Returns
  true or false

Stable:
  ICU 2.4

Definition at line 193 of file utf.h.

## ◆ U_IS_SURROGATE_LEAD

#define U_IS_SURROGATE_LEAD | ( |  | c | ) | (((c)&0x400)==0)

Assuming c is a surrogate code point (U_IS_SURROGATE(c)), is it a lead surrogate?

Parameters

  c | 32-bit code point

Returns
  true or false

Stable:
  ICU 2.4

Definition at line 202 of file utf.h.

## ◆ U_IS_SURROGATE_TRAIL

#define U_IS_SURROGATE_TRAIL | ( |  | c | ) | (((c)&0x400)!=0)

Assuming c is a surrogate code point (U_IS_SURROGATE(c)), is it a trail surrogate?

Parameters

  c | 32-bit code point

Returns
  true or false

Stable:
  ICU 4.2

Definition at line 211 of file utf.h.

## ◆ U_IS_TRAIL

#define U_IS_TRAIL | ( |  | c | ) | (((c)&0xfffffc00)==0xdc00)

Is this code point a trail surrogate (U+dc00..U+dfff)?

Parameters

  c | 32-bit code point

Returns
  true or false

Stable:
  ICU 2.4

Definition at line 185 of file utf.h.

## ◆ U_IS_UNICODE_CHAR

#define U_IS_UNICODE_CHAR | ( |  | c | ) |

Value:
((uint32_t)(c)<0xd800 || \
(0xdfff<(c) && (c)<=0x10ffff && !U_IS_UNICODE_NONCHAR(c)))
U_IS_UNICODE_NONCHAR
#define U_IS_UNICODE_NONCHAR(c)
Is this code point a Unicode noncharacter?
Definition utf.h:130

Is c a Unicode code point value (0..U+10ffff) that can be assigned a character?

Code points that are not characters include:

- single surrogate code points (U+d800..U+dfff, 2048 code points)
- the last two code points on each plane (U+__fffe and U+__ffff, 34 code points)
- U+fdd0..U+fdef (new with Unicode 3.1, 32 code points)
- the highest Unicode code point value is U+10ffff

This means that all code points below U+d800 are character code points, and that boundary is tested first for performance.

Parameters

  c | 32-bit code point

Returns
  true or false

Stable:
  ICU 2.4

Definition at line 151 of file utf.h.

## ◆ U_IS_UNICODE_NONCHAR

#define U_IS_UNICODE_NONCHAR | ( |  | c | ) |

Value:
((c)>=0xfdd0 && \
((c)<=0xfdef || ((c)&0xfffe)==0xfffe) && (c)<=0x10ffff)

Is this code point a Unicode noncharacter?

Parameters

  c | 32-bit code point

Returns
  true or false

Stable:
  ICU 2.4

Definition at line 130 of file utf.h.