4 ms·

I realize you're joking, but probably some of it came from limitations of the Era. As recently as early 2000s, I had to use a 68k assembler that had a limit of

I realize you're joking, but probably some of it came from limitations of the Era. As recently as early 2000s, I had to use a 68k assembler that had a limit of something like 8 or 10 characters for a label. The really annoying part was you could have longer names, but it would silently ignore any extra. We're still stuck with other decisions that were driven by size constraints (like the separation of /bin and /usr/bin, IIRC).

int_19h 6y ago
It comes from the limitations of some early pre-standard C compilers. It was fairly common to use fixed-length arrays, to avoid heap allocations for perf and memory usage reasons. This included identifiers; but then you had to decide on the maximum size - since most identifiers would be fairly short anyway, so a large array would be wasted space. Since the first edition of ANSI/ISO C was trying to codify the already-existing common practices for maximum portability, it reflects those existing limits (5.2.4.1 "Translation limits"): "The implementation shall be able to translate and execute at least one program that contains at least one instance of every one of the following limits: ... 31 significant initial characters in an internal identifier or a macro name 6 significant initial characters in an external identifier" If you look at many abbreviated function names from the C stdlib, they are specifically 6 characters long - strcpy etc. I wouldn't be surprised if the 6-char external identifier limit goes all the way back to the first K&R C compilers.