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Verg

using CRT with DLLs [RESOLVED, aka Verg is a dope]

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I've searched around... but can't seem to come up with a solution to this... Much of our base code is built into static .libs, with either the /MT or /MTd switch, depending on which type of configuration (Debug/Release/etc...) Naturally, these switches map directly to which version(s) of the CRT are linked in. Now, building a DLL using this code seems to be impossible; if I link with /MT or /MTd, the linker complains that it can't find a "main" (or symbol "_main")... this being a DLL, there isn't one... ... and if I link the DLL using /MD or /MDd, there are conflicts (symbols already being defined, etc...) ----------------- Does this mean: I have to build all the base code with the /MD and /MDd switches and link them in? Isn't linking with /MD(d) virtually guaranteeing I'll have to redistribute MSVCRT(71)(D).dll with any app that uses the .dll? ----------------- And... if I build the DLL with the /MD versions of the CRT... can it still be called from code built with the /MT versions? Thanks for any reply. Chad [EDIT TO ADD] I've seen this from MSDN... but it doesn't really answer the question... although I'm nearly positive I'll have to re-build each of the .libs just for the .dll... and almost sure the .dll would still work with /MT(d) code calling it... just not "positive". That's really the only question... hopefully, I don't have to build *everything* with /MD(d)... [Edited by - Verg on July 24, 2005 11:49:08 AM]

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Ah, nevermind... this seems to answer it:



You can link your DLL with CRTDLL.LIB/MSVCRT.LIB regardless of what your .EXE
is linked with if you avoid mixing CRT data structures and passing CRT file
handles or CRT FILE* pointers to other modules.

When mixing library types adhere to the following:

• CRT file handles may only be operated on by the CRT module that created them.

• CRT FILE* pointers may only be operated on by the CRT module that created them.

• Memory allocated with the CRT function malloc() may only be freed or
reallocated by the CRT module that allocated it.

To illustrate this, consider the following example:


- .EXE is linked with MSVCRT.LIB
- DLL A is linked with LIBCMT.LIB
- DLL B is linked with CRTDLL.LIB


If the .EXE creates a CRT file handle using _create() or _open(), this file
handle may only be passed to _lseek(), _read(), _write(), _close(), etc. in the
.EXE file. Do not pass this CRT file handle to either DLL. Do not pass a CRT
file handle obtained from either DLL to the other DLL or to the .EXE.


If DLL A allocates a block of memory with malloc(), only DLL A may call free(),
_expand(), or realloc() to operate on that block. You cannot call malloc() from
DLL A and try to free that block from the .EXE or from DLL B.


NOTE: If all three modules were linked with CRTDLL.LIB or all three were linked
with MSVCRT.LIb, these restrictions would not apply.

When linking DLLs with LIBC.LIB, be aware that if there is a possibility that
such a DLL will be called by a multithreaded program, the DLL will not support
multiple threads running in the DLL at the same time, which can cause major
problems. If there is a possibility that the DLL will be called by multithreaded
programs, be sure to link it with one of the libraries that support
multithreaded programs (LIBCMT.LIB, CRTDLL.LIB or MSVCRT.LIB).

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