For a small, fixed Morse alphabet in C, use a table of strings when clarity matters most; consider packed bytes when table size is a real constraint. For decoding incoming dots and dashes, a trie-shaped state machine is usually a more natural fit than either character-to-code table. The right choice depends on whether you are encoding or decoding, what characters you support, and what your target actually needs.
Choose a representation for the direction of conversion
A Morse encoder starts with a character and looks up its dot-and-dash pattern. A decoder starts with dots and dashes and follows them until it can identify a character. Those are different lookup problems, so one data structure need not serve both.
- Character to Morse: use a string table for a clear, direct mapping; use packed bytes if compact table data is important.
- Morse to character: use a binary trie or equivalent state machine that branches on each dot or dash.
- Both directions: keep separate structures or generate them from a shared definition if that makes the supported alphabet easier to maintain. This is a design inference from the different lookup directions, not a measured performance result.
Compare the main approaches
| Representation | Natural use | Strength | Trade-off |
|---|---|---|---|
| Array of string literals | Encoding a known character | Readable, easy to inspect, and straightforward to pass to formatting or signal-output code. | Stores pattern characters and string terminators; requires a defined indexing and unsupported-character policy. Embedded.com |
| Packed byte per character | Compact fixed encoding table | Combines symbol count and dot/dash data; shifts and masks recover the pattern. | Less obvious to read and debug; the bit layout must be documented precisely. Embedded.com |
| Binary trie or state machine | Decoding dots and dashes | Each signal selects a branch toward a character; implementations can use a compact table. One published implementation uses a 100-byte trie table, not counting any broader program costs. Nullprogram, 2020 | It solves the reverse lookup problem, and the decoder must define invalid paths and how it recognizes the end of a character. |
| Switch or generated table | Small fixed character sets or generated implementations | Can make supported characters and exceptions explicit. | No comparative benchmark establishes a general speed or size advantage over the other approaches. |
Use a string table when readability is the priority
An array of pointers to NUL-terminated strings makes the mapping visible: each supported character refers to a literal pattern such as .-. That directness helps when the table is small, when values are likely to be reviewed or edited, and when downstream code already accepts strings.
Plan the lookup policy alongside the table. For example, an implementation can normalize lowercase ASCII letters to uppercase and report unsupported characters through an error path. That is one possible policy, not a universal Morse or C requirement. A table also needs deliberate indexing: decide whether entries are indexed by an alphabet offset, a character value, or another mapping, and validate input before indexing.
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Pack patterns only with an explicit bit convention
A packed representation can put a symbol count and the dot/dash pattern into one byte, then recover symbols using shifts and masks. This avoids storing each pattern as a sequence of character bytes and a terminator, but it exchanges easy inspection for compactness.
Document the representation next to its encoder and decoder. At minimum, specify:
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- Which bits encode the number of Morse symbols.
- Which bit represents a dot and which represents a dash.
- The order in which the first symbol and later symbols occupy the pattern bits.
- What unused or padding bits mean, and how the code handles the longest supported pattern.
Without those rules, a byte value is difficult to verify by sight and fragile to change. Do not assume packed storage is faster: the cited example reports a faster byte version in its particular program, but does not establish a portable result across C compilers, processors, or workloads. Embedded.com’s comparison describes the performance explanation as uncertain.
Use a trie or state machine to decode
For decoding, treat each dot and dash as a branch. Starting at the root, consume one signal at a time; when the path reaches a terminal entry, the entry identifies a character. A compact implementation can encode the branch transitions and terminal values in tables rather than searching every possible Morse string. Nullprogram’s C-oriented example demonstrates this shape.
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The input stream still needs boundaries. Morse patterns alone do not identify where one letter ends and the next begins, so the decoder must receive or infer character and word gaps. It must also decide what to do when a dot or dash follows a path with no valid continuation, or when a character boundary arrives at a nonterminal path.
Keep Morse timing out of the lookup table
If the program only prints textual patterns, its stored strings or packed values need not include timing delays. Put timing in the signal-output layer instead. International Morse timing is expressed in multiples of the dot unit:
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| Signal or gap | Duration |
|---|---|
| Dot | 1 unit |
| Dash | 3 units |
| Gap between elements of one character | 1 unit |
| Gap between letters | 3 units |
| Gap between words | 7 units |
Under the PARIS timing convention, a word occupies 50 timing units; a 2026 tutorial states the dot duration in milliseconds as 1200 / WPM under that convention. These figures describe signal timing, not the speed of a C lookup routine. Embedded.com; Morse Tools, 2026
Define the supported alphabet and error behavior
Do not let the data structure silently define your input contract. State which characters the program accepts, how it handles letter case, and what happens on unsupported input. International Morse includes 26 letters, 10 digits, and 12 standard punctuation characters under ITU-R M.1677-1; charts may list additional familiar punctuation as common additions rather than part of that standard set. Morse Code Team’s chart, updated August 2026
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A recent C tutorial describes a 36-entry lookup table for A–Z and digits, which is a useful scope for a simple encoder, but it is not a complete punctuation table. Morse Tools, 2026
Benchmark the target before optimizing
There is no source-backed, portable speed ranking for string tables, packed bytes, tries, and switches. The older comparison reports that its byte version ran faster in its own program, while leaving the reason uncertain. Treat that as an observation about that example—not a rule for other targets.
If size or execution time is binding, compare implementations using the same supported alphabet, compiler settings, target processor, and workload. Measure the whole relevant cost: table storage, code size, conversion work, and any output or input processing that dominates the lookup itself. Otherwise, choose the representation that makes the supported behavior easiest to verify and maintain.
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