I thought that after I did undef, Perl could reuse the memory that was freed.

It does.

However, it looks like after freeing memory, the program still causes Perl to run out of memory.

Because the second structure uses more memory (to build if not when complete) than the first.

In reply to Re: out of memory problem after undef by ikegami
in thread out of memory problem after undef by sduser81

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