6.2.6 Numerical input and output

procedure: number->string z

procedure: number->string z radix

Radix must be an exact integer, either 2, 8, 10, or 16. If omitted, radix defaults to 10. The procedure ‘number->string’ takes a number and a radix and returns as a string an external representation of the given number in the given radix such that

(let ((number number)
      (radix radix))
  (eqv? number
        (string->number (number->string number
                                        radix)
                        radix)))

is true. It is an error if no possible result makes this expression true.

If z is inexact, the radix is 10, and the above expression can be satisfied by a result that contains a decimal point, then the result contains a decimal point and is expressed using the minimum number of digits (exclusive of exponent and trailing zeroes) needed to make the above expression true [howtoprint], [howtoread]; otherwise the format of the result is unspecified.

The result returned by ‘number->string’ never contains an explicit radix prefix.

Note: The error case can occur only when z is not a complex number or is a complex number with a non-rational real or imaginary part.

Rationale: If z is an inexact number represented using flonums, and the radix is 10, then the above expression is normally satisfied by a result containing a decimal point. The unspecified case allows for infinities, NaNs, and non-flonum representations.

procedure: string->number string

procedure: string->number string radix

Returns a number of the maximally precise representation expressed by the given string. Radix must be an exact integer, either 2, 8, 10, or 16. If supplied, radix is a default radix that may be overridden by an explicit radix prefix in string (e.g. "#o177"). If radix is not supplied, then the default radix is 10. If string is not a syntactically valid notation for a number, then ‘string->number’ returns #f.

(string->number "100")                 ⇒  100
(string->number "100" 16)              ⇒  256
(string->number "1e2")                 ⇒  100.0
(string->number "15##")                ⇒  1500.0

Note: The domain of ‘string->number’ may be restricted by implementations in the following ways. ‘String->number’ is permitted to return #f whenever string contains an explicit radix prefix. If all numbers supported by an implementation are real, then ‘string->number’ is permitted to return #f whenever string uses the polar or rectangular notations for complex numbers. If all numbers are integers, then ‘string->number’ may return #f whenever the fractional notation is used. If all numbers are exact, then ‘string->number’ may return #f whenever an exponent marker or explicit exactness prefix is used, or if a # appears in place of a digit. If all inexact numbers are integers, then ‘string->number’ may return #f whenever a decimal point is used.

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