Why does C have these weird translation limits (section 2.2.4.1)?

Question

I was just browsing the C standard the other day, and the chapter about translation limits really had me stumped. Why are some translation limits 2^n, others 2^n+1 and others 2^n-k (for some small k)?

Here are just some examples:

• 15 nesting levels of compound statements, iteration control structures, and selection control structures

• 31 declarators nested by parentheses within a full declarator

• 32 expressions nested by parentheses within a full expression

• 31 significant initial characters in an internal identifier or a macro name

• 511 external identifiers in one translation unit

• 509 characters in a logical source line

• 257 case labels for a switch statement (excluding those for any nested switch statements)

Why isn't everything simply a power of two?

Answer 1

Why isn't everything simply a power of two?

To me, most of them look like 2ⁿ - 1, even the line length, once you add carriage return and line feed.

These are minimum limits, by the way. Compilers are allowed to exceed them.