CH>
  > My thinking is that the run-time library in the DLL doesn't
  > share it's [sic] memory arena information with the RTL in the
  > main EXE.
CH>

  This is indeed what is happening.

CH>
  >           If this is the case, the I believe that I have
  > found a workaround: use a function pointer to pass the
  > DLL's malloc calls back to the EXE so it can call malloc
  > directly.  I can use the workaround, but I'd rather fix
  > this problem properly, say, by using only one copy of the
  > RTL.
CH>

  That is not the correct solution.

  A DLL that allocates a resource, such as memory from a heap, and then
  passes that memory to its caller *must* provide a function to release
  that resource.

  It's symmetrical; it's neat.  Most of all, it reduces the coupling
  between the client and the DLL.

  Your solution (using a global C++ RTL) restricts your DLL to only being
  usable in applications written with *one* version of *one* C++ compiler.

  > JdeBP <
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