NSString（十六进制）到字节

Question

Objective-C 中是否有任何方法可以将十六进制字符串转换为字节？例如，@"1156FFCD3430AA22" 到 无符号字符数组 {0x11, 0x56, 0xFF, ...}。

Answer 1

我能想到的最快的 NSString 类别实现（一些示例的混合物）：

- (NSData *)dataFromHexString {
    const char *chars = [self UTF8String];
    int i = 0, len = self.length;

    NSMutableData *data = [NSMutableData dataWithCapacity:len / 2];
    char byteChars[3] = {'\0','\0','\0'};
    unsigned long wholeByte;

    while (i < len) {
        byteChars[0] = chars[i++];
        byteChars[1] = chars[i++];
        wholeByte = strtoul(byteChars, NULL, 16);
        [data appendBytes:&wholeByte length:1];
    }

    return data;
}

它比 wookay 的解决方案快了近 8 倍。 NSScanner 相当慢。

Answer 2

@interface NSString (NSStringHexToBytes)
-(NSData*) hexToBytes ;
@end



@implementation NSString (NSStringHexToBytes)
-(NSData*) hexToBytes {
  NSMutableData* data = [NSMutableData data];
  int idx;
  for (idx = 0; idx+2 <= self.length; idx+=2) {
    NSRange range = NSMakeRange(idx, 2);
    NSString* hexStr = [self substringWithRange:range];
    NSScanner* scanner = [NSScanner scannerWithString:hexStr];
    unsigned int intValue;
    [scanner scanHexInt:&intValue];
    [data appendBytes:&intValue length:1];
  }
  return data;
}
@end



/// example
unsigned char bytes[] = { 0x11, 0x56, 0xFF, 0xCD, 0x34, 0x30, 0xAA, 0x22 };
NSData* expectedData = [NSData dataWithBytes:bytes length:sizeof(bytes)];
NSLog(@"data %@", [@"1156FFCD3430AA22" hexToBytes]);
NSLog(@"expectedData isEqual:%d", [expectedData isEqual:[@"1156FFCD3430AA22" hexToBytes]]);

Answer 3

scanHexInt: 和 NSScanner 的类似方法可能有助于执行您想要的操作，但您可能需要打破首先将其串成较小的块，在这种情况下，手动进行翻译可能比使用 NSScanner 更简单。

Answer 4

不是以你正在做的方式。您需要编写自己的方法来获取每两个字符，将它们解释为 int，并将它们存储在数组中。

Answer 5

修改方法，

/* Converts a hex string to bytes.
 Precondition:
 . The hex string can be separated by space or not.
 . the string length without space or 0x, must be even. 2 symbols for one byte/char
 . sample input: 23 3A F1 OR 233AF1, 0x23 0X231f 2B
 */

+ (NSData *) dataFromHexString:(NSString*)hexString
{
    NSString * cleanString = [Util cleanNonHexCharsFromHexString:hexString];
    if (cleanString == nil) {
        return nil;
    }

    NSMutableData *result = [[NSMutableData alloc] init];

    int i = 0;
    for (i = 0; i+2 <= cleanString.length; i+=2) {
        NSRange range = NSMakeRange(i, 2);
        NSString* hexStr = [cleanString substringWithRange:range];
        NSScanner* scanner = [NSScanner scannerWithString:hexStr];
        unsigned int intValue;
        [scanner scanHexInt:&intValue];
        unsigned char uc = (unsigned char) intValue;
        [result appendBytes:&uc length:1];
    }
    NSData * data = [NSData dataWithData:result];
    [result release];
    return data;
}

/* Clean a hex string by removing spaces and 0x chars.
 . The hex string can be separated by space or not.
 . sample input: 23 3A F1; 233AF1; 0x23 0x3A 0xf1
 */

+ (NSString *) cleanNonHexCharsFromHexString:(NSString *)input
{
    if (input == nil) {
        return nil;
    }

    NSString * output = [input stringByReplacingOccurrencesOfString:@"0x" withString:@""
                                    options:NSCaseInsensitiveSearch range:NSMakeRange(0, input.length)];
    NSString * hexChars = @"0123456789abcdefABCDEF";
    NSCharacterSet *hexc = [NSCharacterSet characterSetWithCharactersInString:hexChars];
    NSCharacterSet *invalidHexc = [hexc invertedSet];
    NSString * allHex = [[output componentsSeparatedByCharactersInSet:invalidHexc] componentsJoinedByString:@""];
    return allHex;
}

Answer 6

Swift 2.2 中的首次尝试：

func hexStringToBytes(hexString: String) -> NSData? {
    guard let chars = hexString.cStringUsingEncoding(NSUTF8StringEncoding) else { return nil}
    var i = 0
    let length = hexString.characters.count

    let data = NSMutableData(capacity: length/2)
    var byteChars: [CChar] = [0, 0, 0]

    var wholeByte: CUnsignedLong = 0

    while i < length {
        byteChars[0] = chars[i]
        i+=1
        byteChars[1] = chars[i]
        i+=1
        wholeByte = strtoul(byteChars, nil, 16)
        data?.appendBytes(&wholeByte, length: 1)
    }

    return data
}

或者，作为 String 的扩展：

extension String {

    func dataFromHexString() -> NSData? {
        guard let chars = cStringUsingEncoding(NSUTF8StringEncoding) else { return nil}
        var i = 0
        let length = characters.count

        let data = NSMutableData(capacity: length/2)
        var byteChars: [CChar] = [0, 0, 0]

        var wholeByte: CUnsignedLong = 0

        while i < length {
            byteChars[0] = chars[i]
            i+=1
            byteChars[1] = chars[i]
            i+=1
            wholeByte = strtoul(byteChars, nil, 16)
            data?.appendBytes(&wholeByte, length: 1)
        }

        return data
    }
}

这是一项持续进行中的工作，但到目前为止似乎运行良好。

进一步的优化和更深入的讨论可以在代码审查中找到。

Answer 7

如果字符串像这样返回错误值的几种解决方案
“DBA”

“DBA”字符串的正确数据为 “\x0D\xBA”（int 值：3514）

如果您获得了数据， 不是这样的“\x0D\xBA”这意味着你得到了一个错误的字节，因为值会不同，例如你得到了这样的数据“\xDB\x0A” > int 值为 56074

这里重写解决方案：

+ (NSData *)dataFromHexString:(NSString *) string {
    if([string length] % 2 == 1){
        string = [@"0"stringByAppendingString:string];
    }

    const char *chars = [string UTF8String];
    int i = 0, len = (int)[string length];

    NSMutableData *data = [NSMutableData dataWithCapacity:len / 2];
    char byteChars[3] = {'\0','\0','\0'};
    unsigned long wholeByte;

    while (i < len) {
        byteChars[0] = chars[i++];
        byteChars[1] = chars[i++];
        wholeByte = strtoul(byteChars, NULL, 16);
        [data appendBytes:&wholeByte length:1];
    }
    return data;

}