如何检查NSData对象是否包含子NSData？

Question

我有一个NSData对象，它包含我需要的一些数据。我想要做的是找出数据"FF D8“( JPEG数据的开始)的位置。

我怎样才能做到这样的工作呢？

Answer 1

首先得到范围，然后得到数据：

// The magic start data object is only created once safely and 
// then reused each time
static NSData* magicStartData = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
  static const uint8_t magic[] = { 0xff, 0xd8 };
  magicStartData = [NSData dataWithBytesNoCopy:(void*)magic length:2 freeWhenDone:NO];
});

// assume data is the NSData with embedded data
NSRange range = [data rangeOfData:magicStartData options:0 range:NSMakeRange(0, [data length])];
if (range.location != NSNotFound) {
  // This assumes the subdata doesn't have a specific range and is just everything
  // after the magic, otherwise adjust
  NSData* subdata = [data subdataWithRange:NSMakeRange(range.location, [data length] - range.location)];
}

Answer 2

试试NSData rangeOfData:options:range:

    NSData *data = /* Your data here */;

    UInt8 bytes_to_find[] = { 0xFF, 0xD8 };
    NSData *dataToFind = [NSData dataWithBytes:bytes_to_find
                                        length:sizeof(bytes_to_find)];

    NSRange range = [data rangeOfData:dataToFind
                              options:kNilOptions
                                range:NSMakeRange(0u, [data length])];

    if (range.location == NSNotFound) {
        NSLog(@"Bytes not found");
    }
    else {
        NSLog(@"Bytes found at position %lu", (unsigned long)range.location);
    }