NSString(十六进制)到字节

Question

Objective-C中是否有将十六进制字符串转换为字节的方法？例如@"1156FFCD3430AA22"一个unsigned char array {0x11, 0x56, 0xFF, ...}.

Answer 1

我能想到的最快的NSString类别实现(一些示例的鸡尾酒):

- (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8倍.NSScanner非常慢.

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

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。