C等价于Java"Character.digit(hexText.charAt(i),16)"

Question

我正在尝试使用C将十六进制字符串解码回二进制数据.我在Java中完成了这项工作,并且在C中具有等效的编码功能,但无法完全解码.看哪...

Java代码:

private static String encodeToHex(byte[] bytes) {
    StringBuilder stringBuilder = new StringBuilder();
    for (byte b : bytes) {
        stringBuilder.append(String.format("%02x", b & 0xff));
    }
    return stringBuilder.toString();
}

private static byte[] decodeFromHex(String hexText) {
    int length = hexText.length();
    byte[] data = new byte[length / 2];
    for (int i = 0; i < length; i += 2) {
        data[i / 2] = (byte) ((Character.digit(hexText.charAt(i), 16) << 4) + Character.digit(hexText.charAt(i + 1), 16));
    }
    return data;
}

C代码:

void encodeToHex(const unsigned char *encryptedText, const size_t length, char *hexEncodedText) {
    for (int i = 0; i < length; i++) {
        if (i == 0) {
            sprintf(hexEncodedText, "%02x", encryptedText[i] & 0xff);
        } else {
            sprintf(hexEncodedText + strlen(hexEncodedText), "%02x", encryptedText[i] & 0xff);
        }
    }
}

// The poor attempt. Note, I do not write C like a native
void hexDecode(char *hexEncodedText, unsigned char *decodedCipherText) {
    int length = strlen(hexEncodedText);
    unsigned char data[length / 2];
    for (int i = 0; i < length; i += 2) {
        data[i / 2] = (char) ((hexEncodedText[i] << 4) + (hexEncodedText[i + 1]));
    }
    memcpy(decodedCipherText, data, length / 2);
}

我想我想要寻找的是Java的C等价物Character.digit(hexText.charAt(i), 16).任何有关如何做到这一点的想法？

提前致谢.

Answer 1

C没有直接等价的Character.digit,但由于您的基数硬编码为16,您可以自己编写一个:

int hexDigit(char digit) {
    static const char *hexDigits = "0123456789ABCDEF";
    return strchr(hexDigits, toupper(digit)) - hexDigits;
}