unresolved external symbol, but dumpbin says it's ok

Question

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,class std::allocator > 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 ``` Wha…

Accepted Answer

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.

unresolved external symbol, but dumpbin says it's ok

Solution

Problem