Code Point - Definition

Definition

The notion of a code point is used for abstraction, to distinguish both:

  • the number from an encoding as a sequence of bits, and
  • the abstract character from a particular graphical representation (glyph).

This is because one may wish to make these distinctions:

  • encode a particular code space in different ways, or
  • display a character via different glyphs.

For Unicode, the particular sequence of bits is called a code unit – for the UCS-4 encoding, any code point is encoded as 4-byte (octet) binary numbers, while in the UTF-8 encoding, different code points are encoded as sequences from one to four bytes long, forming a self-synchronizing code. See comparison of Unicode encodings for details. Code points are normally assigned to abstract characters. An abstract character is not a graphical glyph but a unit of textual data. However code points may also be left reserved for future assignment (most of the Unicode code space is unassigned), or given other designated functions.

The distinction between a code point and the corresponding abstract character is not pronounced in Unicode, but is evident for many other encoding schemes, where numerous code pages may exist for a single code space.

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