NSData 和十六进制字符串

从十六进制字符串中获取 NSData

+ (NSData *)dataFromHexString:(NSString *)string
{
    string = [string lowercaseString];
    NSMutableData *data= [NSMutableData new];
    unsigned char whole_byte;
    char byte_chars[3] = {'\0','\0','\0'};
    int i = 0;
    int length = (int) string.length;
    while (i < length-1) {
        char c = [string characterAtIndex:i++];
        if (c < '0' || (c > '9' && c < 'a') || c > 'f')
            continue;
        byte_chars[0] = c;
        byte_chars[1] = [string characterAtIndex:i++];
        whole_byte = strtol(byte_chars, NULL, 16);
        [data appendBytes:&whole_byte length:1];
    }
    return data;
}

从数据中获取十六进制字符串：

+ (NSString *)hexStringForData:(NSData *)data
{
    if (data == nil) {
        return nil;
    }
    
    NSMutableString *hexString = [NSMutableString string];
    
    const unsigned char *p = [data bytes];
    
    for (int i=0; i < [data length]; i++) {
        [hexString appendFormat:@"%02x", *p++];
    }
    
    return hexString;
}