如何将NSData转换为NSString十六进制字符串？

Question

当我调用-description一个NSData对象时,我看到一个NSData对象字节的十六进制字符串,如:

<f6e7cd28 0fc5b5d4 88f8394b af216506 bc1bba86 4d5b483d>

我希望将数据的这种表示(减去lt/gt引号)放入内存中,NSString这样我就可以使用它.我不想调用-[NSData description]然后只修剪lt/gt引号(因为我认为这不是NSData公共界面的保证方面,并且将来会发生变化.

将NSData对象表示为NSString对象(除了调用之外-description)的最简单方法是什么？

Answer 1

请记住,任何String(format: ...)解决方案都会非常慢(对于大数据)

NSData *data = ...;
NSUInteger capacity = data.length * 2;
NSMutableString *sbuf = [NSMutableString stringWithCapacity:capacity];
const unsigned char *buf = data.bytes;
NSInteger i;
for (i=0; i<data.length; ++i) {
  [sbuf appendFormat:@"%02X", (NSUInteger)buf[i]];
}

如果你需要更高性能的东西试试这个:

static inline char itoh(int i) {
    if (i > 9) return 'A' + (i - 10);
    return '0' + i;
}

NSString * NSDataToHex(NSData *data) {
    NSUInteger i, len;
    unsigned char *buf, *bytes;

    len = data.length;
    bytes = (unsigned char*)data.bytes;
    buf = malloc(len*2);

    for (i=0; i<len; i++) {
        buf[i*2] = itoh((bytes[i] >> 4) & 0xF);
        buf[i*2+1] = itoh(bytes[i] & 0xF);
    }

    return [[NSString alloc] initWithBytesNoCopy:buf
                                          length:len*2
                                        encoding:NSASCIIStringEncoding
                                    freeWhenDone:YES];
}

Swift 4.2版本

extension Data {

    var hexString: String? {
        return withUnsafeBytes { (bytes: UnsafePointer<UInt8>) in
            let charA = UInt8(UnicodeScalar("a").value)
            let char0 = UInt8(UnicodeScalar("0").value)

            func itoh(_ value: UInt8) -> UInt8 {
                return (value > 9) ? (charA + value - 10) : (char0 + value)
            }

            let hexLen = count * 2
            let ptr = UnsafeMutablePointer<UInt8>.allocate(capacity: hexLen)

            for i in 0 ..< count {
                ptr[i*2] = itoh((bytes[i] >> 4) & 0xF)
                ptr[i*2+1] = itoh(bytes[i] & 0xF)
            }

            return String(bytesNoCopy: ptr,
                               length: hexLen,
                             encoding: .utf8,
                         freeWhenDone: true)
        }
    }
}

Answer 2

我同意解决方案不要调用description哪个是保留用于调试,所以好点和好问题:)

最简单的解决方案是循环遍历字节NSData并从中构造NSString.使用[yourData bytes]访问字节,并建立串入一个NSMutableString.

以下是使用NSData类别实现此示例的示例

@interface NSData(Hex)
-(NSString*)hexRepresentationWithSpaces_AS:(BOOL)spaces;
@end

@implementation NSData(Hex)
-(NSString*)hexRepresentationWithSpaces_AS:(BOOL)spaces
{
    const unsigned char* bytes = (const unsigned char*)[self bytes];
    NSUInteger nbBytes = [self length];
    //If spaces is true, insert a space every this many input bytes (twice this many output characters).
    static const NSUInteger spaceEveryThisManyBytes = 4UL;
    //If spaces is true, insert a line-break instead of a space every this many spaces.
    static const NSUInteger lineBreakEveryThisManySpaces = 4UL;
    const NSUInteger lineBreakEveryThisManyBytes = spaceEveryThisManyBytes * lineBreakEveryThisManySpaces;
    NSUInteger strLen = 2*nbBytes + (spaces ? nbBytes/spaceEveryThisManyBytes : 0);

    NSMutableString* hex = [[NSMutableString alloc] initWithCapacity:strLen];
    for(NSUInteger i=0; i<nbBytes; ) {
        [hex appendFormat:@"%02X", bytes[i]];
        //We need to increment here so that the every-n-bytes computations are right.
        ++i;

        if (spaces) {
            if (i % lineBreakEveryThisManyBytes == 0) [hex appendString:@"\n"];
            else if (i % spaceEveryThisManyBytes == 0) [hex appendString:@" "];
        }
    }
    return [hex autorelease];
}
@end

用法:

NSData* data = ...
NSString* hex = [data hexRepresentationWithSpaces_AS:YES];

Answer 3

只是想补充说@ PassKits的方法可以使用Swift 3非常优雅地编写,因为Data现在是一个集合.

extension Data { 
    var hex: String {
        var hexString = ""
        for byte in self {
            hexString += String(format: "%02X", byte)
        }

        return hexString
    }
}

要么 ...

extension Data {
    var hex: String {
        return self.map { b in String(format: "%02X", b) }.joined()
    }
}

甚至 ...

extension Data {
    var hex: String {
        return self.reduce("") { string, byte in
            string + String(format: "%02X", byte)
        }
    }
}

Answer 4

我最喜欢@ Erik_Aigner的答案.我只是重构了一下:

NSData *data = [NSMutableData dataWithBytes:"acani" length:5];
NSUInteger dataLength = [data length];
NSMutableString *string = [NSMutableString stringWithCapacity:dataLength*2];
const unsigned char *dataBytes = [data bytes];
for (NSInteger idx = 0; idx < dataLength; ++idx) {
    [string appendFormat:@"%02x", dataBytes[idx]];
}

Answer 5

在Swift中,您可以创建扩展.

extension NSData {

    func toHexString() -> String {

        var hexString: String = ""
        let dataBytes =  UnsafePointer<CUnsignedChar>(self.bytes)

        for (var i: Int=0; i<self.length; ++i) {
            hexString +=  String(format: "%02X", dataBytes[i])
        }

        return hexString
    }
}

然后你可以简单地使用:

let keyData: NSData = NSData(bytes: [0x00, 0xFF], length: 2)

let hexString = keyData.toHexString()
println("\(hexString)") // Outputs 00FF