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    <p>Ruby FFI tries to be symmetric about who owns memory - if you allocate it (i.e. the C code), you have to free it. Conversely, if FFI allocates it, it alone can free it.</p> <p>You didn't post your FreeStrings() function, but assuming it looks a bit like:</p> <pre><code>void FreeStringArray(char **strings, int len) { for (int i = 0; i &lt; len; ++i) { delete[] strings[i]; } // Do _NOT_ free 'strings' itself, that is managed by FFI } </code></pre> <p>And you use it thusly:</p> <pre><code>module SomeDll extend FFI::Library ffi_lib 'SomeDll.dll' attach_function :get_strings, :ReturnAnArrayOfStrings, [:pointer], :int attach_function :free_strings, :FreeStringArray, [ :pointer, :int ], :void end include SomeDll count = get_strings(nil) strings = FFI::MemoryPointer.new :pointer, count get_strings strings strings.get_array_of_string(0, count).each do |value| puts value end # free each element of the array free_strings(strings, count) </code></pre> <p>Then that should work. </p> <p>The equivalent C code would be:</p> <pre><code>int count = ReturnArrayOfStrings(NULL); // Allocate an array for the pointers. i.e. FFI::MemoryPointer.new :pointer, count char **ptr_array = (char **) calloc(count, sizeof(char *)); ReturnArrayOfStrings(ptr_array); for (int i = 0; i &lt; count; ++i) { printf("string[%d]=%s\n", i, ptr_array[i]); } // Free each element of the array (but not the array itself) FreeStringArray(ptr_array, count); // free the array itself. i.e FFI::MemoryPointer garbage-collecting its memory free(ptr_array); </code></pre>
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    1. COyep, that's exactly what I ended up doing. Thanks for the clear code explanation!
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