UTF-32 (or UCS-4) is a protocol for encoding Unicode characters that uses exactly 32 bits for each Unicode code point. All other Unicode transformation formats use variable-length encodings. The UTF-32 form of a character is a direct representation of its codepoint.
Because UTF-32 uses 4 bytes for every character it is quite space inefficient. Specifically, non-BMP characters are so rare in most texts, they may as well be considered non-existent for sizing discussions, making UTF-32 between two and four times the size of other encodings.
Though a fixed number of bytes per code point seems convenient, it is not used as much as the other Unicode encodings. It makes truncation slightly easier but not significantly so compared to UTF-8 and UTF-16. It does not make calculating the displayed width of a string any easier except in very limited cases, since even with a “fixed width” font there may be more than one code point per character position (combining marks) or more than one character position per code point (for example CJK ideographs). Combining marks also mean editors cannot treat one code point as being the same as one unit for editing.
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