objective-c - 如何将十六进制字符串转换为字节

Question

如何将十六进制字符串转字节和字节转十六进制字符串？我有 oc 代码，但我不能快速编写你能帮我吗 ？非常感谢

+ (NSData *)convertHexToDataBytes:(NSString *)hexStr {
    NSMutableData *dataBytes = [NSMutableData data];
    int idx;
    for (idx = 0; idx + 2 <= hexStr.length; idx += 2) {
        NSRange range = NSMakeRange(idx, 2);
        NSString *singleHexStr = [hexStr substringWithRange:range];
        NSScanner *scanner = [NSScanner scannerWithString:singleHexStr];
        unsigned int intValue;
        [scanner scanHexInt:&intValue];
        [dataBytes appendBytes:&intValue length:1];
    }
    return dataBytes;
}

+ (NSString *)convertDataBytesToHex:(NSData *)dataBytes {
    if (!dataBytes || [dataBytes length] == 0) {
        return @"";
    }
    NSMutableString *hexStr = [[NSMutableString alloc] initWithCapacity:[dataBytes length]];
    [dataBytes enumerateByteRangesUsingBlock:^(const void *bytes, NSRange byteRange, BOOL *stop) {
        unsigned char *dataBytes = (unsigned char *)bytes;
        for (NSInteger i = 0; i < byteRange.length; i ++) {
            NSString *singleHexStr = [NSString stringWithFormat:@"%x", (dataBytes[i]) & 0xff];
            if ([singleHexStr length] == 2) {
                [hexStr appendString:singleHexStr];
            } else {
                [hexStr appendFormat:@"0%@", singleHexStr];
            }
        }
    }];
    return hexStr;
}

我是这样写的 swift

    class func convertHex(toDataBytes hexStr: String?) -> Data? {
        var dataBytes = Data()
        var idx: Int
        idx = 0
        while idx + 2 <= (hexStr?.count ?? 0) {
            let range = NSRange(location: idx, length: 2)
            let singleHexStr = (hexStr as NSString?)?.substring(with: range)
            let scanner = Scanner(string: singleHexStr ?? "")
            var intValue: UInt
            scanner.scanHexInt32(&UInt32(intValue))
            dataBytes.append(&intValue, count: 1)
            idx += 2
        }
        return dataBytes
    }

它的错误是:无法将不可变值作为 inout 参数传递:函数调用返回不可变值如何解决？

Answer 1

回答您的直接问题:UInt32(intValue) 创建一个新的(常量)值，其地址不能用 & 获取。所以

var intValue: UInt
scanner.scanHexInt32(&UInt32(intValue))

应该是

var intValue: UInt32 = 0
scanner.scanHexInt32(&intValue)

和

dataBytes.append(&intValue, count: 1)

无法编译，因为 &intValue 是一个指向整数的指针，而不是指向 UInt8 的指针。在这里你可以做

dataBytes.append(UInt8(intValue))

因为该值已知适合单个字节。

话虽如此，所有从 String 到 NSString 的转换都是不需要的。将该 Objective-C 代码更“swift ”地转换为 Swift 将是

func convertHex(toDataBytes hexStr: String) -> Data {
    var dataBytes = Data()
    var startPos = hexStr.startIndex
    while let endPos = hexStr.index(startPos, offsetBy: 2, limitedBy: hexStr.endIndex) {
        let singleHexStr = hexStr[startPos..<endPos]
        let scanner = Scanner(string: String(singleHexStr))
        var intValue: UInt32 = 0
        scanner.scanHexInt32(&intValue)
        dataBytes.append(UInt8(intValue))
        startPos = endPos
    }
    return dataBytes
}

另一种方法(包括错误检查)参见示例 hex/binary string conversion in Swift