How do I check whether an NSData object contains a sub-NSData?

问题

I have an NSData object which contains some data I need. What I wanted to do is to find out the position of data "FF D8" (start of JPEG data)

How can I achieve work like this?

回答1:

First get the range, then get the data:

// 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)];
}

回答2:

Try 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);
    }

来源：https://stackoverflow.com/questions/18477710/how-do-i-check-whether-an-nsdata-object-contains-a-sub-nsdata

标签

cocoa

nsdata