NSData dataWithContentsOfFile与NSInputStream

Question

I have to process XML, now using NSInputStream breaks my code as I have to rewrite lots of things.

Will dataWithContentsOfFile entire file into memory, or only read contents requested for getBytes method?

I am using NSData as input parameter to NSXMLParser, I wonder is there any documentation regarding this?

There is no documentation on apple's doc regarding internals of NSData's dataWithContentsOfFile or its implementation.

Answer 1

When you allocating NSData for NSXMALParser ,it means creating data buffer for that object and every object occupy memory (RAM) ,because iPhone IOS know very well how to use virtual memory. When you reading entire data from the file, it occupying object data and if the data size is more than a few(depended upon OS algo) memory pages, the object uses virtual memory management. A data object can also wrap preexisting data, regardless of how the data was allocated. The object contains no information about the data itself (such as its type); the responsibility for deciding how to use the data lies with the client. In particular, it will not handle byte-order swapping when distributed between big-endian and little-endian machines.
I recommend you to read again this link https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/BinaryData/BinaryData.html#//apple_ref/doc/uid/10000037i its related to iOS. But yes one thing concern with you ….in IOS there is type of owner of object. One is user and another one is IOS object. if you creating NSData that means you allocating memory buffer and assigning data pointer to this veriable, but at that moment entire data is resides inside memory. Its our assumption, but during this period IOS know how to handle this scenario. IOS uses vertual memory technique to handle data pages.