I have 2 MFC projects.
A library project uses Multi-byte Character set.
An executable project uses Unicode Character set.
I only wrote the library project and have to use it in the executable.
One of the library's functions returns a CString.
When I try to put that CString into a variable in my unicode project and compile
I get this:
Error 3 error LNK2001: unresolved external symbol "public: class
ATL::CStringT<wchar_t,class StrTraitMFC_DLL<wchar_t,class
ATL::ChTraitsCRT<wchar_t> > > __thiscall CTextDisplay::GetString(void)"
(?GetString#CTextDisplay##QAE?AV?$CStringT#_WV? $StrTraitMFC_DLL#_WV?
$ChTraitsCRT#_W#ATL#####ATL##XZ)
I don't mind converting on any of the projects. I just want a way for the library to be able to return a string to the executable project.
Switching either project to the other character set is not an option as they are both gigantic.
Thanks in advance.
There is really no such thing as returning a CString. There are CStringA's and CStringW's and it sounds like you are receiving one and want the other. You will need to use MultiByteToWideChar and/or WideCharToMultiByte to convert.
http://msdn.microsoft.com/en-us/library/windows/desktop/dd319072(v=vs.85).aspx
Related
I am getting this error as part of my VC C++ project.
libcmtd.lib(exe_main.obj) error lnk2001 unresolved external symbol main
It's simple Hello world project for now which I am trying to build in Release mode in x64. I am using MTd as runtime library.
Did you use Unicode for this project? Look into the project properties. If you used Unicode the function should be "wmain" instead of "main", I believe. And also if you used the typed version for strings regarding Unicode you should use "_tmain".
The same rule applies to string operations, iostream etc. E.g. "_ftprint" instead of "fprint" etc.
I'm new to MFC.
I'm trying to make a DLL in MFC, which links to another DLL.
The problem is when I try and compile, I get a LNK2019 error thrown at me for a function present in the DLL which I'm trying to link.
LNK2019 is when the DLL or the function inside the DLL is not being found.
I've taken all steps, the DLL is placed in a known location, the lib is placed in a known location too, it's been added in the additional dependencies, all correct switches have been applied ( ones I know of anyway ).
I've used Dependency walker and I know the DLL, to which I'm trying to link, exposes this function.
I've other examples of use of the function, and I'm trying to use it exactly like it.
The .lib and .dll are in agreement, i.e., they're consistent with each other.
But still the error persists.
EDIT
This is the error message :
Error 2 error LNK2019: unresolved external symbol
"__declspec(dllimport) public: bool __thiscall
PwServer::Connect(wchar_t const *,unsigned long,unsigned long *)"
(_imp?Connect#PwServer##QAE_NPB_WKPAK#Z) referenced in function
"public: bool __thiscall CPwServer::Connect(class
ATL::CStringT > >,unsigned long,unsigned long *)"
(?Connect#CPwServer##QAE_NV?$CStringT#_WV?$StrTraitMFC_DLL#_WV?$ChTraitsCRT#_W#ATL#####ATL##KPAK#Z)
And this is the call I use to access the DLL.
bool conn = PwSrv->Connect(_T(""));
Dumpbin Export of the function :
25BE6 ?Connect#PwServer##QAE_NPBGKPAK#Z 25BE6 __imp_?Connect#PwServer##QAE_NPBGKPAK#Z
Is there something else which needs to be dine in case of linking a MFC DLL with a regular one, like adding AFX_EXT_ or something?
Kindly advise in this.
Thank you.
UPDATE
Seems all that was required was to toggle the flag set in Project Properties>>C/C++>>Language>>Treat wchar_t as a built in type to NO. I'd never bothered with the flag before, so didn't know. The Linker error was there...
OK. Now I've another problem. The toggling of wchar_t solved the problem of the DLL linking with another MFC DLL, but now my application cannot find the entry point in my DLL. In dependency walker, it shows a mismatch between CString which the application is sending, and the Unsigned Short..which my DLL is accepting ( as a result of thewchar_t turned off, presumably )
Assuming you correctly included the .lib file for the DLL (most of the time this is down to differences in the compiler settings. e.g. UNICODE setting).
Check that the .lib is actually being loaded by setting the 'Show Progress' Linker settings to VERBOSE.
Run DUMPBIN on the LIB file to check that the exported functions are the same as the ones the linker is trying to import.
ie
dumpbin /ALL mylib.lib > exports.txt
If the name decoration is slightly different that'll give you a clue as to the problem.
I have two projects in one solution in Visual Studio. One of the projects (application) depends on another (library). The library has a method:
int foo(_TCHAR*);
It is properly defined in header and implemented. In the application I call the method like this:
int bar(_TCHAR* str) {
return foo(str);
}
The error I am getting is
error LNK2001: unresolved external symbol "public: int __cdecl
foo(char *)"
The method signature is exactly the same and the same type of variable is being used.
The reason behind the linker not being able to match the methods is the mismatched Character Set option in projects General Properties page.
The library project had this option set to Use Unicode Character Set and the application to Use Multi-Byte Character Set.
Unifying the Character Set in both projects fixed this error.
I have 2 projects in c++ (MFC)
One is a library project which im using in the second one (an executable one).
They work together great, until I call a function from the regular project that takes a CString as argument. I get a linker error like this
error LNK2019: unresolved external symbol "public: void __thiscall
CTextDisplay::SetText1(class ATL::CStringT<wchar_t,class StrTraitMFC_DLL<wchar_t,
class ATL::ChTraitsCRT<wchar_t> > >)" (?SetText1#CTextDisplay##QAEXV?$CStringT#_WV?
$StrTraitMFC_DLL#_WV?$ChTraitsCRT#_W#ATL#####ATL###Z) referenced in function
"public: void __thiscall CManualPane::SetBeadCountFor(int,double)"
(?SetBeadCountFor#CManualPane##QAEXHN#Z) C:\source\IQ-Project\IQ\ManualPane.obj IQ
The executable project has its character set to UNICODE but the Library has it set to Multy-Byte chatacter set. I really can't change them without getting ridiculous amounts of errors.
Any suggestions?
Edit: The reason we have different settings in these two projects is because the Executable project is basically an external project that my group didn't build or create. We just had to bring it in and use it. The library project is something we've all been working on for a couple years.
When you include the headers of the library project in the executable, there is likely a typedef which is used in the declaration of the function. Since the executable uses UNICODE, the declaration is now in UNICODE. However, the library implementation is still in MultiByte and so the definition doesn't match the declaration leading to the linker error.
Look into how these typedefs are being setup, and you might be able to do some special #define, #undef around the included header.
In the end it proved to be a better idea to avoid having unicode and multybyte projects in the same solution so I moved it all to unicode and went from there
I'm trying to write some simple test code for the Crypto++ library for a project. I have yet to manage to get my own code to build though. It compiles fine, the problem comes in linking. I'm still pretty new to Visual Studios, but I'm using VS10. The errors I'm getting are:
1>sec_test.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall CryptoPP::DES::Base::ProcessAndXorBlock(unsigned char const *,unsigned char const *,unsigned char *)const " (?ProcessAndXorBlock#Base#DES#CryptoPP##UBEXPBE0PAE#Z)
1>sec_test.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall CryptoPP::DES::Base::UncheckedSetKey(unsigned char const *,unsigned int,class CryptoPP::NameValuePairs const &)" (?UncheckedSetKey#Base#DES#CryptoPP##UAEXPBEIABVNameValuePairs#3##Z)
I've tried everything I can find in the documentation in terms of linking. I've never linked against a DLL before, but these are the errors I get when I try to. If I try to do what I think is linking against the static library version, I get even more.
I should note, I'm trying to test pure DES at the moment. In particular, here are the API calls I'm making, just to be safe:
DES::Encryption DES_encrypt;
DES_encrypt.SetKey(key, 64);
DES_encrypt.ProcessAndXorBlock(plaintext, NULL, ciphertext);
DES::Decryption DES_decrypt;
DES_decrypt.SetKey(key, 64);
DES_decrypt.ProcessAndXorBlock(ciphertext, NULL, decrypted);
If anyone can help, or point me in the right direction, I'd be much obliged.
First thing to check is your project properties (right click on project, click Properties).
External libraries need to be specified in the Linker->Input->Additional Dependencies field, either by absolute path or in conjunction with the other VS path properties.
You can look in Linker->Command Line and check that the .lib files you want are actually being passed to the linker.
An alternate method is to turn off the Suppress Startup Banner option in the Linker->General options, and then check the build output to make sure it has what you want.
If you know that the libraries you want are being linked, another useful trick is to check the output of the strings command (in linux or cygwin) or dumpbin /HEADERS in the VS command prompt. You can look through the output of these commands for the symbol VS claims is missing to verify that it really is defined in the .lib file. Sometimes larger software packages have multiple .lib files, so this can help make sure you are linking the one that has the symbol you want.