TheAlgorithms/Go · error

invalid hexadecimal string:

Error message

invalid hexadecimal string: 

What it means

hexToBinary validates the string with isValidHex and returns this error (with the offending input appended) when the string is not valid hexadecimal. The dynamic message embeds the rejected value to ease debugging. It precedes the per-character parse loop.

Source

Thrown at conversion/hexadecimaltobinary.go:35

	"strings"
)

var isValidHex = regexp.MustCompile("^[0-9A-Fa-f]+$").MatchString

// hexToBinary() function that will take Hexadecimal number as string,
// and return its Binary equivalent as a string.
func hexToBinary(hex string) (string, error) {
	// Trim any leading or trailing whitespace
	hex = strings.TrimSpace(hex)

	// Check if the hexadecimal string is empty
	if hex == "" {
		return "", errors.New("input string is empty")
	}

	// Check if the hexadecimal string is valid
	if !isValidHex(hex) {
		return "", errors.New("invalid hexadecimal string: " + hex)
	}

	// Parse the hexadecimal string to an integer
	var decimal int64
	for i := 0; i < len(hex); i++ {
		char := hex[i]
		var value int64
		if char >= '0' && char <= '9' {
			value = int64(char - '0')
		} else if char >= 'A' && char <= 'F' {
			value = int64(char - 'A' + 10)
		} else if char >= 'a' && char <= 'f' {
			value = int64(char - 'a' + 10)
		} else {
			return "", errors.New("invalid character in hexadecimal string: " + string(char))
		}
		decimal = decimal*16 + value
	}

View on GitHub (pinned to 5ba447ec5f)

Solutions

1. Strip a leading "0x"/"0X" prefix and remove whitespace/separators before calling.
2. Pre-validate with a regexp ^[0-9a-fA-F]+$ and reject early.
3. Parse the error message to identify the offending string and fix the input source.

Example fix

// before
out, err := conversion.HexToBinary("0x1A3F") // invalid hexadecimal string: 0x1A3F
// after
clean := strings.TrimPrefix(strings.TrimPrefix(raw, "0x"), "0X")
out, err = conversion.HexToBinary(clean)

var hexRe = regexp.MustCompile(`^[0-9a-fA-F]+$`)
func isHex(s string) bool {
    s = strings.TrimPrefix(strings.TrimPrefix(s, "0x"), "0X")
    return hexRe.MatchString(s)
}

out, err := conversion.HexToBinary(hex)
if err != nil {
    if strings.HasPrefix(err.Error(), "invalid hexadecimal string:") {
        return fmt.Errorf("bad hex input: %w", err)
    }
    return err
}

When it happens

Trigger: Calling the hex conversion with strings like "0x1A" (prefix not stripped), "GG", "12 34", or hex with a sign or decimal point.

Common situations: Copy-pasting hex values that include the "0x"/"0X" prefix, whitespace, or byte separators (":" or "-") from dump tools.

Related errors

• invalid character in hexadecimal string:
• not a valid binary string
• input string is empty
• binary number must be in range 0 to 2^(31-1)
• integer must have +ve value

AI-assisted analysis of TheAlgorithms/Go@5ba447ec5f (2026-09-02). Data as JSON: /api/errors/a5cc64eb6247f474. Report an issue: GitHub.