Source: atoc.go in package strconv


package strconv

const fnParseComplex = "ParseComplex"

convErr splits an error returned by parseFloatPrefix into a syntax or range error for ParseComplex.

func convErr(err error, s string) (syntax, range_ error) {
	if x, ok := err.(*NumError); ok {
		x.Func = fnParseComplex
		x.Num = s
		if x.Err == ErrRange {
			return nil, x
		}
	}
	return err, nil
}

ParseComplex converts the string s to a complex number with the precision specified by bitSize: 64 for complex64, or 128 for complex128. When bitSize=64, the result still has type complex128, but it will be convertible to complex64 without changing its value. The number represented by s must be of the form N, Ni, or N±Ni, where N stands for a floating-point number as recognized by ParseFloat, and i is the imaginary component. If the second N is unsigned, a + sign is required between the two components as indicated by the ±. If the second N is NaN, only a + sign is accepted. The form may be parenthesized and cannot contain any spaces. The resulting complex number consists of the two components converted by ParseFloat. The errors that ParseComplex returns have concrete type *NumError and include err.Num = s. If s is not syntactically well-formed, ParseComplex returns err.Err = ErrSyntax. If s is syntactically well-formed but either component is more than 1/2 ULP away from the largest floating point number of the given component's size, ParseComplex returns err.Err = ErrRange and c = ±Inf for the respective component.

func ParseComplex(s string, bitSize int) (complex128, error) {
	size := 64
	if bitSize == 64 {
		size = 32 // complex64 uses float32 parts
	}

	orig := s

Remove parentheses, if any.

	if len(s) >= 2 && s[0] == '(' && s[len(s)-1] == ')' {
		s = s[1 : len(s)-1]
	}

	var pending error // pending range error, or nil

Read real part (possibly imaginary part if followed by 'i').

	re, n, err := parseFloatPrefix(s, size)
	if err != nil {
		err, pending = convErr(err, orig)
		if err != nil {
			return 0, err
		}
	}
	s = s[n:]

If we have nothing left, we're done.

	if len(s) == 0 {
		return complex(re, 0), pending
	}

Otherwise, look at the next character.

	switch s[0] {

Consume the '+' to avoid an error if we have "+NaNi", but do this only if we don't have a "++" (don't hide that error).

		if len(s) > 1 && s[1] != '+' {
			s = s[1:]
		}

If 'i' is the last character, we only have an imaginary part.

		if len(s) == 1 {
			return complex(0, re), pending
		}
		fallthrough
	default:
		return 0, syntaxError(fnParseComplex, orig)
	}

Read imaginary part.

	im, n, err := parseFloatPrefix(s, size)
	if err != nil {
		err, pending = convErr(err, orig)
		if err != nil {
			return 0, err
		}
	}
	s = s[n:]
	if s != "i" {
		return 0, syntaxError(fnParseComplex, orig)
	}
	return complex(re, im), pending