Reserve contiguous space in memory with NSMutableData

Question

How can I force NSMutableData to reserve contiguous memory, in the same section? I have a fair amout of data arriving piece by piece, and the performance is not satisfactory. The total size of my data will be constant.

Create the `NSMutableData` object with either `dataWithCapacity:` or `initWithCapacity:`. — rmaddy, Jul 11 '13 at 16:39

score 2 · Accepted Answer · answered Jul 11 '13 at 16:37

2

NSMutableData should store all data contiguously. Internally it is using a "stretchy" buffer resized with realloc. You can create with [NSMutableData dataWithLength:];

Why not use an NSData if the size is constant?

Also why are you worrying about NSMutableData performance. Did instruments profile show a performance problem?

answered Jul 11 '13 at 16:37

Justin Meiners

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Hi @Justin, Ok I´ll explain a little more, the buffer size is constant but I write to this by parts, the data comes from an external accessory so each time I receive data I need to copy it into the rigth position. I´m worry about performance since I receive 64KB of information from the accessory and it is taking 3+ seconds (for me it is a lot) so I´m trying to optimize the code. – Jose Alberto Diaz Jul 11 '13 at 16:53
@JoseAlbertoDiaz write into the data using memcpy([data mutableBytes] + offset, source, size); or maybe the more cocoa friendly replaceBytesInRange:withBytes: – Justin Meiners Jul 11 '13 at 17:05

Reserve contiguous space in memory with NSMutableData

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