unresolved external symbol, but dumpbin says it's ok

问题

I downloaded Crypto++ 5.62 and built it with default project settings. In my project I set up the path to cryptopp.lib and defined its name in "Additional Dependencies". Both Crypto++ and my project - VS 2008.

During building of my project I get:

main.obj : error LNK2001: unresolved external symbol 
  "class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const CryptoPP::DEFAULT_CHANNEL" (?DEFAULT_CHANNEL@CryptoPP@@3V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@B)

main.obj : error LNK2001: unresolved external symbol 
  "bool (__cdecl* CryptoPP::g_pAssignIntToInteger)(class type_info const &,void *,void const *)" (?g_pAssignIntToInteger@CryptoPP@@3P6A_NABVtype_info@@PAXPBX@ZA)

dumpbin /all cryptopp.lib shows me in the public symbols section

19471C _imp_?DEFAULT_CHANNEL@CryptoPP@@3V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@B

1D6F30 __imp_?g_pAssignIntToInteger@CryptoPP@@3P6A_NABVtype_info@@PAXPBX@ZA

What's wrong then? Why the linker can't find the symbols?

upd:

linker command line from my project settings

/OUT:"C:\Projects\crypto_hash\Debug\crypto_hash.exe" /NOLOGO /LIBPATH:"e:\libs\cryptopp\cryptopp562\cryptopp\Win32\DLL_Output\Debug" /MANIFEST /MANIFESTFILE:"Debug\crypto_hash.exe.intermediate.manifest" /MANIFESTUAC:"level='asInvoker' uiAccess='false'" /DEBUG /PDB:"C:\Projects\crypto_hash\Debug\crypto_hash.pdb" /DYNAMICBASE /NXCOMPAT /MACHINE:X86 /ERRORREPORT:PROMPT cryptopp.lib kernel32.lib user32.lib gdi32.lib winspool.lib comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib uuid.lib odbc32.lib odbccp32.lib

回答1:

Try adding CRYPTOPP_IMPORTS to your project defines.

From config.h:

#ifdef CRYPTOPP_EXPORTS
# define CRYPTOPP_IS_DLL
# define CRYPTOPP_DLL __declspec(dllexport)
#elif defined(CRYPTOPP_IMPORTS)
# define CRYPTOPP_IS_DLL
# define CRYPTOPP_DLL __declspec(dllimport)
#else
# define CRYPTOPP_DLL
#endif

Or include Crypto++'s dll.h. It sets CRYPTOPP_IMPORTS:

#if !defined(CRYPTOPP_IMPORTS) && !defined(CRYPTOPP_EXPORTS) && !defined(CRYPTOPP_DEFAULT_NO_DLL)
# ifdef CRYPTOPP_CONFIG_H
#  error To use the DLL version of Crypto++, this file must be included before any other Crypto++ header files.
# endif
# define CRYPTOPP_IMPORTS
#endif

If that does not work...

g_pAssignIntToInteger is from algparams.cpp:

$ grep -R g_pAssignIntToInteger *
algparam.cpp:PAssignIntToInteger g_pAssignIntToInteger = NULL;
algparam.h:CRYPTOPP_DLL extern PAssignIntToInteger g_pAssignIntToInteger;
algparam.h:     if (!(g_pAssignIntToInteger != NULL && typeid(T) == typeid(int) && g_pAssignIntToInteger(valueType, pValue, &m_value)))
integer.cpp:    if (!g_pAssignIntToInteger)
integer.cpp:        g_pAssignIntToInteger = AssignIntToInteger;

Looking at the declaration in algparam.h:

// to allow the linker to discard Integer code if not needed.
typedef bool (CRYPTOPP_API * PAssignIntToInteger)(const std::type_info &valueType, void *pInteger, const void *pInt);
CRYPTOPP_DLL extern PAssignIntToInteger g_pAssignIntToInteger;

And the implementation in algparam.cpp:

#ifndef CRYPTOPP_IMPORTS
...

NAMESPACE_BEGIN(CryptoPP)    
PAssignIntToInteger g_pAssignIntToInteger = NULL;
...

So you might need to change the implementation to ensure the code uses g_pAssignIntToInteger (to keep it from being discarded). Unfortunately, nothing comes to mind at the moment.

DEFAULT_CHANNEL is declared in cryptlib.h and has storage allocated in cryptolib.cpp:

$ grep -R DEFAULT_CHANNEL *
...
cryptlib.cpp:const std::string DEFAULT_CHANNEL;
...
cryptlib.h:extern CRYPTOPP_DLL const std::string DEFAULT_CHANNEL;
...

This might be a different problem since I'm not used to seeing issues with DEFAULT_CHANNEL. See how CRYPTOPP_IMPORTS works for you, and then ask a different question since this might be a different problem.

来源：https://stackoverflow.com/questions/22686709/unresolved-external-symbol-but-dumpbin-says-its-ok

标签

c++

unresolved-external

crypto++