iphone a little write files, read the specific contents of the document

iphone to file written characters, can have similar C # Append method, ie a little write files, each time having to write, first remove the contents of the file, save, add new content, and then written to the file . Also in reading, can not remove all the part and then read (subdataWithRange) they need, but directly read out the contents of their needs?
Reply:
Possible.
NSFileHandle
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NSFileHandle
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NSFileHandle

Reply:
Right, thank you