parse-integer

(parse-integer string &key start end radix junk-allowed)

Parses an integer from a string, skipping surrounding whitespace. :start/:end bound the parsed region, :radix selects the base (default 10) and :junk-allowed, when non-nil, stops at the first non-digit and returns the integer parsed so far (or nil if none). Without :junk-allowed, a region that is no integer -- a non-whitespace character after the digits, no digit at all, an empty region -- signals a parse-error. A nil :end means the length. A :radix that is not an integer from 2 to 36 signals a type-error of (INTEGER 2 36) before anything is read, digit-char-p's, even for an empty string or with :junk-allowed. A bound that is negative, not an integer (a nil :start included) or past the string's length, or a start past its end, signals the type-error subseq signals for the same range. The second return value is the position where parsing stopped, ready to feed back into :start. The full keyword set and both values work identically on every backend; usable as a first-class value (#'parse-integer).

(parse-integer "42") returns 42, and (parse-integer "x9x" :start 1 :end 2) returns 9 by parsing only the bounded region.