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What is Hight and Low surrogate character in .NET?

ICSM Computer 738 03 Jun 2025

Ask by ICSM Computer

Updated 03 Jun 2025

1 Answers

ICSM Computer 03 Jun 2025

In .NET (and Unicode in general), high and low surrogate characters are used to represent Unicode code points that cannot be represented in a single 16-bit char (i.e., characters beyond the Basic Multilingual Plane, BMP — those with code points above U+FFFF).

Surrogate Pairs: What They Are

.NET uses UTF-16 encoding for strings. UTF-16 represents:

Code points from U+0000 to U+FFFF (BMP) in a single char (16-bit).
Code points from U+10000 to U+10FFFF using a pair of char values — one high surrogate and one low surrogate.

This pair is called a surrogate pair.

High Surrogate

Unicode range: U+D800 to U+DBFF
Decimal range: 55296 to 56319
Always appears first in a surrogate pair

Low Surrogate

Unicode range: U+DC00 to U+DFFF
Decimal range: 56320 to 57343
Always appears second in a surrogate pair

Example

Consider the emoji 😁 (Unicode code point U+1F601):

In UTF-16, this is encoded as:

High Surrogate: \uD83D
Low Surrogate: \uDE01

string emoji = "😁";
char highSurrogate = emoji[0]; // '\uD83D'
char lowSurrogate  = emoji[1]; // '\uDE01'

.NET API Methods Related to Surrogates

You can use these static methods from the Char class:

bool isHigh = Char.IsHighSurrogate(char c);
bool isLow = Char.IsLowSurrogate(char c);
bool isSurrogatePair(char high, char low);

Example:

char hs = '\uD83D';
char ls = '\uDE01';

bool valid = Char.IsSurrogatePair(hs, ls); // true

Summary Table

Type	Unicode Range	Decimal Range	Notes
High Surrogate	U+D800–U+DBFF	55296–56319	First char in a pair
Low Surrogate	U+DC00–U+DFFF	56320–57343	Second char in a pair

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