NSData and its mutable subclass NSMutableData provide
data objects, object-oriented wrappers for byte buffers. Data objects let simple allocated buffers (that is, data with no embedded pointers) take on the behavior of Foundation objects.
NSData creates static data objects, and NSMutableData creates
dynamic data objects. NSData and NSMutableData are typically used for data storage and are
also useful in Distributed Objects applications, where data contained in data objects can be copied or moved between applications.
The size of the data is subject to a theoretical limit of about 8 ExaBytes (in practice, the limit should not be a factor).
NSData is “toll-free bridged” with its Core Foundation counterpart, CFDataRef.
See “Toll-Free
Bridging” for more information on toll-free bridging.
+ data+ dataWithBytes:length:+ dataWithBytesNoCopy:length:+ dataWithBytesNoCopy:length:freeWhenDone:+ dataWithContentsOfFile:+ dataWithContentsOfFile:options:error:+ dataWithContentsOfURL:+ dataWithContentsOfURL:options:error:+ dataWithData:– initWithBase64EncodedData:options:– initWithBase64EncodedString:options:– initWithBytes:length:– initWithBytesNoCopy:length:– initWithBytesNoCopy:length:deallocator:– initWithBytesNoCopy:length:freeWhenDone:– initWithContentsOfFile:– initWithContentsOfFile:options:error:– initWithContentsOfURL:– initWithContentsOfURL:options:error:– initWithData:– initWithBase64Encoding: Deprecated
in iOS 7.0+ dataWithContentsOfMappedFile: Deprecated
in iOS 5.0– initWithContentsOfMappedFile: Deprecated
in iOS 5.0– bytes– description– enumerateByteRangesUsingBlock:– getBytes:length:– getBytes:range:– subdataWithRange:– rangeOfData:options:range:– getBytes: Deprecated
in iOS 4.0– base64EncodedDataWithOptions:– base64EncodedStringWithOptions:– base64Encoding Deprecated
in iOS 7.0
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iOS 基础类解析 - NSData,布布扣,bubuko.com
原文：http://blog.csdn.net/opengl_es/article/details/24838161