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POHow could pairing new[] with delete possibly lead to memory leak only?
 

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  1. POHow could pairing new[] with delete possibly lead to memory leak only?
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    <p>First of all, using <code>delete</code> for anything allocated with <code>new[]</code> is undefined behaviour according to C++ standard.</p> <p>In Visual C++ 7 such pairing can lead to one of the two consequences.</p> <p>If the type new[]'ed has trivial constructor and destructor VC++ simply uses <code>new</code> instead of <code>new[]</code> and using <code>delete</code> for that block works fine - <code>new</code> just calls "allocate memory", <code>delete</code> just calls "free memory".</p> <p>If the type new[]'ed has a non-trivial constructor or destructor the above trick can't be done - VC++7 has to invoke exactly the right number of destructors. So it prepends the array with a <code>size_t</code> storing the number of elements. Now the address returned by <code>new[]</code> points onto the first element, not onto the beginning of the block. So if <code>delete</code> is used it only calls the destructor for the first element and the calls "free memory" with the address different from the one returned by "allocate memory" and this leads to some error indicaton inside HeapFree() which I suspect refers to heap corruption.</p> <p>Yet every here and there one can read false statements that using <code>delete</code> after <code>new[]</code> leads to a memory leak. I suspect that anything size of heap corruption is much more important than a fact that the destructor is called for the first element only and possibly the destructors not called didn't free heap-allocated sub-objects.</p> <p>How could using <code>delete</code> after <code>new[]</code> possibly lead only to a memory leak on some C++ implementation?</p>
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    1. USKevin Panko
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    1. COTo all answerers: the question is how it can lead to **only** a memory leak, i.e., how it can possibly **not** cause heap corruption.
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      1. USThomas
    2. COQuite easily. It all depends on how the memory management is written. Since this is undefined by the standard all answers are just speculation (but I am sure that I could write a version that would not crash the heap but did leak memory). The memory management sub-sytem is as fast and efficient as possible. The standard has given them a set of pre and post conditions under which the sub-system can be optimized. Break these conditions and you have undefined behavior (probably heap corruption). In debug, stability not speed is the goal of the memory sub-system. Hence leaking is more likely.
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      1. USMartin York
    3. COhttp://stackoverflow.com/questions/1553382/pod-freeing-memory-is-delete-equal-to-delete/1553407#1553407
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