TheAlgorithms/Go · error

invalid character in hexadecimal string: %c

Error message

invalid character in hexadecimal string: %c

What it means

Defense-in-depth inside the accumulation loop: even after the regex check, a character that maps to no digit (theoretically unreachable for ASCII input, possible for multi-byte runes) aborts conversion naming the character.

Source

Thrown at conversion/hexadecimaltodecimal.go:51

		hexStr = hexStr[2:]
	}

	// Validate the hexadecimal string
	if !isValidHexadecimal(hexStr) {
		return 0, fmt.Errorf("invalid hexadecimal string")
	}

	var decimalValue int64
	for _, char := range hexStr {
		var digit int64
		if char >= '0' && char <= '9' {
			digit = int64(char - '0')
		} else if char >= 'A' && char <= 'F' {
			digit = int64(char - 'A' + 10)
		} else if char >= 'a' && char <= 'f' {
			digit = int64(char - 'a' + 10)
		} else {
			return 0, fmt.Errorf("invalid character in hexadecimal string: %c", char)
		}
		decimalValue = decimalValue*16 + digit
	}

	return decimalValue, nil
}

View on GitHub (pinned to 5ba447ec5f)

Solutions

1. Rely on the regex validation upstream; treat this as an invariant failure
2. Report the exact offending character to aid debugging
3. Log and skip rather than fail if streaming conversion is required

When it happens

Trigger: Thrown at conversion/hexadecimaltodecimal.go:51 when the library encounters an invalid state.

Common situations: See trigger scenarios.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

AI-assisted analysis of TheAlgorithms/Go@5ba447ec5f (2026-09-02). Data as JSON: /api/errors/64ec2d82821bae58. Report an issue: GitHub.