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qt5crypto++unresolved-external

Correct way of linking crypto++ library with my application

I am trying to use Crypto++ library in my Qt application.

Qt version is 5.3.0 Compiled with VS2013 running on Windows 8.1

Crypto++ Lib compiled with VS2013

Here is the section of my .pro file which links the lib

win32: LIBS += -L$$PWD/cryptopp562/Win32/DLL_Output/Release/ -lcryptopp

INCLUDEPATH += $$PWD/cryptopp562
DEPENDPATH += $$PWD/cryptopp562

Everything appears to be fine. However I get two issues.

  • I am unable to compile the debug version. I assume that this is because I have release version of .lib file

  • When I try to compile my application, I get the following errors

crypto.obj:-1: error: LNK2019: unresolved external symbol "class std::basic_string,class std::allocator > const CryptoPP::DEFAULT_CHANNEL" (?DEFAULT_CHANNEL@CryptoPP@@3V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@B) referenced in function "public: virtual bool __thiscall CryptoPP::Unflushable::Flush(bool,int,bool)" (?Flush@?$Unflushable@VFilter@CryptoPP@@@CryptoPP@@UAE_N_NH0@Z)

I get two such errors and I assume that this is due to two functions which calls the lib which are not getting compiled.

Edit

My observations:

  • It seems like I am linking to correct static lib, i.e. libcrypt.lib and I have used dumpbin utility to ensure that the missing symbols specified by the error are there in the lib file.

  • It appears that though I am specifying in the .pro file, some how the lib is not being referenced by the project. I have put the following line in my .pro file to reference to static lib

    win32: LIBS += -L$$PWD/cryptopp562/Win32/Output/Release/ -lcryptlib

    INCLUDEPATH += $$PWD/cryptopp562 DEPENDPATH += $$PWD/cryptopp562

    win32:!win32-g++ PRE_TARGETDEPS += $$PWD/cryptopp562/Win32/Output/Release/cryptlib.lib else:win32-g++: PRE_TARGETDEPS += $$PWD/cryptopp562/Win32/Output/Release/libcryptlib.a

My question is,

What mistake I am making ?

What is the correct way to link the Crypto++ lib to Qt project.

Solution

  • I'm going to answer the Edit and Comments in a second block.

    After many attempts, finally I am getting this error - cryptlib.lib(cryptlib.obj):-1: error: LNK2038: mismatch detected for 'RuntimeLibrary': value 'MT_StaticRelease' doesn't match value 'MD_DynamicRelease' in main.obj

    Right click on the cryptlib project, and then select Properties.

    Notice the Runtime Library. Crypto++ uses the non-DLL runtime libraries by default; and I suspect QT uses the DLL versions of the runtime library by default. Put another way, Crypto++ uses /MT or /MTd by default. And you need /MD or /MDd for Qt integration.

    enter image description here

    To fix this, have Crypto++ use the DLL version of the runtime library for each Configuration (Debug and Release) and each Platform (Win32 and x64). So your new settings would look like so (notice the addition of DLL):

    enter image description here

    After making the changes, do a Build → Batch Build → Clean and then a Build → Batch Build → [four static LIBs] as described in the other answer.

    Or, you can tell QT to use the non-DLL versions of the runtime library. But nowadays, its usually easiest to use the DLL version of the runtime library for everything.

    In either case (change Crypto++ or change Qt), you will still be using the Crypto++ static LIB. The only difference is the static LIB will be built using the DLL version of the runtime library, and not the non-DLL version of the runtime library.

    By the way, this was documented some time ago at Static Versus Dynamic Linking at Compiling and Integrating Crypto++ into the Microsoft Visual C++ Environment. But I think the solution is unclear.