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PONew NSData with range of old NSData maintaining bytes
 

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    <p>I have a fairly large NSData (or NSMutableData if necessary) object which I want to take a small chunk out of and leave the rest. Since I'm working with large amounts of NSData bytes, I don't want to make a big copy, but instead just truncate the existing bytes. Basically:</p> <ul> <li>NSData *source: &lt; a few bytes I want to discard > + &lt; big chunk of bytes I want to keep ></li> <li>NSData *destination: &lt; big chunk of bytes I want to keep ></li> </ul> <p>There are truncation methods in NSMutableData, but they only truncate the end of it, whereas I want to truncate the beginning. My thoughts are to do this with the methods:</p> <p><strong><em>Note that I used the wrong (copying) method in the original posting. I've edited and fixed it</em></strong></p> <pre><code>- (const void *)bytes </code></pre> <p>and</p> <pre><code>- initWithBytesNoCopy:length:freeWhenDone: </code></pre> <p>However, I'm trying to figure out how to manage memory with these. I'm guessing the process will be like this (I've placed ????s where I don't know what to do):</p> <pre><code>// Get bytes const unsigned char *bytes = (const unsigned char *)[source bytes]; // Offset the start bytes += myStart; // Somehow (m)alloc the memory which will be freed up in the following step ????? // Release the source, now that I've allocated the bytes [source release]; // Create a new data, recycling the bytes so they don't have to be copied NSData destination = [[NSData alloc] initWithBytesNoCopy:bytes length:myLength freeWhenDone:YES]; </code></pre> <p>Thanks for the help!</p>
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    1. COI suppose this is more of a malloc question?
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