[MySQL-plusplus] Compiling under Win32 as Multithreaded-Non-DLL?

Hi,

thank You very much for Your quick reply!

Please find some comments on Your answers inline.

2008/4/22, Warren Young <[email protected]>:
You mean, that building MySQL++ with /MT generates a static library?
This is not the case, as the mysqlpp[_d].dll in that case still is
generated (and needed by the executable). I think the determination
whether to build a dll or lib takes place in the "common" tab of the
project properties where you need to select "static lib" as
"configuration type"...
I do not want to link statically due to LGPL.
Thank You for this hin, but I know this, and we already own a
commercial MySQL license (which I also wrote in my first mail).
That's what I also thought before I tried the following:
* open the mysql++.sln workspace from the vc2003 directory in my VC7.1;
* compile (debug build) without changing settings;
* works w/o linker errors; can execute binaries like simple1.exe etc.;
* change Code Generation for "mysqlpp" project from "Multithreaded
Debug DLL (/MDd)" to "Multithreaded Debug (/MTd)", rebuild all; (note
that simple1 project is still configured as /MDd so I mixed the
flags!)
* works w/o linker errors, can execute binaries like simple1.exe w/o problems;
* change Code Generation for "excommon" to /MTd;
* rebuilding "excommon" results in 3 linker warnings, although mysqlpp
and excommon have now the same /MTd flag: they look like
---8<-------
cmdline.obj : warning LNK4006: '"public: class
std::basic_ostream<char,struct std::char_traits<char> > & __thiscall
std::basic_ostream<char,struct std::char_traits<char>
(??6?$b[email protected]?$[email protected]@std@@@std@@[email protected]@Z)'
bereits in 'mysqlpp_d.lib(mysqlpp_d.dll)' definiert; zweite Definition
wird ignoriert
--->8-------
(have a German VS, message in English means "already defined in
mysqlpp_d.dll, ignoring 2nd definition")
* change Code Generation for "simple1" to /MTd;
* rebuilding "simple1" results in 5 linker errors:
---8<-------
mysqlpp_excommon.lib(mysqlpp_d.dll) : error LNK2005: "public: class
std::basic_ostream<char,struct std::char_traits<char> > & __thiscall
std::basic_ostream<char,struct std::char_traits<char> >::flush(void)"
(?flush@?$[email protected]?$[email protected]@std@@@std@@[email protected])
bereits in mysqlpp_excommon.lib(cmdline.obj) definiert
mysqlpp_excommon.lib(mysqlpp_d.dll) : error LNK2005: "public: class
std::basic_ostream<char,struct std::char_traits<char> > & __thiscall
std::basic_ostream<char,struct std::char_traits<char> >::put(char)"
(?put@?$[email protected]?$[email protected]@std@@@std@@[email protected]@Z)
bereits in mysqlpp_excommon.lib(cmdline.obj) definiert
libcpmtd.lib(cerr.obj) : error LNK2005: "public: void __thiscall
std::basic_ios<char,struct std::char_traits<char>
(?setstate@?$[email protected]?$[email protected]@std@@@std@@[email protected]) bereits
in mysqlpp_excommon.lib(mysqlpp_d.dll) definiert
libcpmtd.lib(cout.obj) : error LNK2005: "public: void __thiscall
std::basic_ios<char,struct std::char_traits<char>
(?setstate@?$[email protected]?$[email protected]@std@@@std@@[email protected]) bereits
in mysqlpp_excommon.lib(mysqlpp_d.dll) definiert
E:\develop\LEOS_SRV\_new\mysql++-3.0.2\vc2003\Debug\simple1.exe :
fatal error LNK1169: Ein oder mehrere mehrfach definierte Symbole
gefunden
--->8-------
(last one meaning "one or more multiple defined symbols found")

I have configured all projects with the same code generation option
(/MTd) and it does *not* work. Any ideas on that?

Thanks for your help in advance.

Best regards,

-oli-
(O. Baum)

Hi again,

in the last days I did some extensive investigations on my problem.

Let me first mention some facts about /MT and /MD and DLL creation:
* It is normally no problem to create a DLL compiled with /MT.
* The EXE which uses this DLL *should* be then also compiled with /MT
to prevent strange effects from happening. These effects are described
here <http://msdn2.microsoft.com/en-us/library/ms235460.aspx>.
* A DLL interface can be designed in a way these effects do not occur.

HOWEVER, one will run into a huge linkage problem IF one compiles a
DLL with /MT AND the DLL interface contains classes which are derived
from C(++)-std-lib's classes (like std::string, std::ostream etc.).
Exactly this is the case in MySQL++: The Query class is derived from
std::ostream, which leads to linkage errors LNK2005 and LNK1169 when
trying to link the MySQL++ DLL with the main program's EXE.
(All links and works correctly if all is compiled with /MD.)

Could anybody help me please?
I am not able to compile my main program's EXE with /MD, because I
need to link MFC statically.
I cannot compile MySQL++ with /MT because then the described "strange
effects" (including corrupt stack, crash when calling CDateTime::str()
etc.) occur.

When I link MySQL++ statically all works, but this is not allowed due
to LGPL restrictions.

Thank you for help in advance!

With best regards,

O. Baum


2008/4/22 O. Baum <[email protected]>:

I don't know of any easy answers. You could:

1. Change the parentage of Query and a whole lot of other classes (Row,
Fields, etc.) If you provided the patches, at best they would be
accepted no earlier than v4, which could be years away. More likely,
this would cause a development fork.

2. Switch to MinGW, which shouldn't have these limitations, but you'd
have to change GUI frameworks, too. If you don't have much code written
yet, this may be practical, but probably not otherwise.

3. Find some other C++ wrapper for MySQL.

4. Forget C++ wrappers, and use the underlying MySQL C API instead.

I am not sure why you insist on having MFC statically linked, while you
don't mind linking MySQL++ dynamically.
I haven't programmed with MFC, but theoretically it should be possible
to link MFC statically to a program compiled with /MD. In that case,
MFC needs to be compiled with /MD as well, but not as a DLL, but as a
static library.