Commodore 64 ?STRING TOO LONG ERROR — How to Fix

What Does This Error Mean?

C64 BASIC strings have a 255-character maximum.
?STRING TOO LONG happens when concatenation or LEFT$/MID$/RIGHT$ produces a result longer than 255.
Split your data into multiple strings (A1$, A2$, A3$) or use a string array.
For very long text, store it in DATA statements and read in chunks.

Affected Models

Commodore 64
Commodore 64C
Commodore 128 in C64 mode
Commodore VIC-20

Common Causes

Concatenation pushed length past 255 — A$ = A$ + B$ in a loop
INPUT or GET concatenated into a single growing string
MID$ produced a result over 255 characters (rare)
Reading a long sequential file into one string

How to Fix It

Find the offending statement.

Run the program, note the line number printed with the error.
LIST that line and look for + on strings, or INPUT inside a loop.
Break the string into pieces.

Replace A$ = A$ + B$ with an array: DIM A$(20).
Each element holds up to 255 chars.
Index them as A$(0), A$(1), A$(2).
Track length before appending.

Add a check: IF LEN(A$)+LEN(B$) > 255 THEN ... do something different.
Either skip, truncate, or move to the next array slot.
For text editors or long buffers: use multiple variables.

Old C64 word processors got around this by chaining strings — line 1 in L1$, line 2 in L2$, etc.
Or by using the cassette buffer and screen memory directly via PEEK and POKE.

Frequently Asked Questions

Why 255 — couldn't they have made it longer?

C64 BASIC was a tight port of Microsoft BASIC.
String length is stored in a single byte, which maxes out at 255.
Some third-party BASIC extensions (Simon's BASIC, BASIC 7.0 on the C128) have the same limit — it's not really fixable without rewriting the interpreter.