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objective-cnsstringdynamic-allocationcalloc

Why can NSString not take ownership of memory allocated with new?

The static analyzer in Xcode 8 (beta 1) is warning me that NSString's initWithBytesNoCopy:length:encoding:freeWhenDone: can't take ownership of memory allocated by new[]. Is this an error? If not, why is this the case?

If I change my allocation to use calloc instead of new[], the warning goes away.

Solution

  • The documentation says this about the freeWhenDone parameter:

    If YES, the receiver releases the memory with free() when it no longer needs the data; if NO it won’t.

    So freeWhenDone literally calls free() when done. To work with new[], it would have to delete[] when done. Hence, the warning message is correct. If you don't want to copy the bytes, then you'll need to set freeWhenDone to NO, and delete[] the bytes when no longer needed.