The C Character Set – part 4.
The C Character Set – part 4.
Here’s Part 4 of an overview of the C character set, assuming you’re continuing a breakdown of the C programming language’s fundamental elements. If you’d like this to match a previous format or style, feel free to share that.
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The C Character Set – Part 4: Trigraphs and Digraphs
What are Trigraphs?
Trigraphs are sequences of three characters that represent a single character not easily available on some keyboards. Although rarely used today, they are part of the C standard for backward compatibility with older systems.
Trigraph Sequences
| Trigraph | Replaces | Description |
|---|---|---|
??= |
# |
Hash / Pound sign |
??/ |
\ |
Backslash |
??' |
^ |
Caret |
??( |
[ |
Left square bracket |
??) |
] |
Right square bracket |
??! |
` | ` |
??< |
{ |
Left curly brace |
??> |
} |
Right curly brace |
??- |
~ |
Tilde |
Example:
Warning: Trigraphs are considered obsolete and can confuse readers. Most compilers disable them by default or issue warnings.
What are Digraphs?
Digraphs are two-character sequences that provide alternate ways to write some punctuation characters, particularly useful on systems where those characters are difficult to type.
Digraph Sequences
| Digraph | Replaces | Description |
|---|---|---|
<: |
[ |
Left square bracket |
:> |
] |
Right square bracket |
<% |
{ |
Left curly brace |
%> |
} |
Right curly brace |
%: |
# |
Hash / Pound sign |
Example:
Note: Unlike trigraphs, digraphs are more accepted but still uncommon in modern codebases.
Summary
-
Trigraphs: Deprecated and rarely used; composed of
??followed by a third character. -
Digraphs: Two-character alternatives for braces, brackets, and the hash sign; supported but rarely necessary.
-
Modern usage: Most modern systems and editors support all characters directly. These constructs mainly exist for compatibility.
Would you like Part 5 to cover character classification (e.g., letters, digits, etc.), or something else like escape sequences, keywords, or operators?