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POError when using dllimport in a DLL client
 

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    <p>Howdi folks, I'm currently creating a DLL and the client which goes with it using the stock procedure mentioned at a lot of places on the internet. Basically, create a DLL project which actually defines a PROJECT_EXPORTS in the Project.h file. Something like this:</p> <pre><code>// Assume the name of the project is SanProj and the header file is SanProj.h #ifdef SANPROJ_EXPORTS #define SANPROJ_API __declspec(dllexport) #else #define SANPROJ_API __declspec(dllimport) #endif </code></pre> <p>Now the normal way of using this header is to include this in all the headers of your API classes and using SANPROJ_EXPORTS for "exporting" declarations when in the DLL and "importing" declarations when used as a client. For e.g. let's say we have a header file with a currency class:</p> <pre><code>// currency.hpp #include "SanProj.h" #include &lt;ostream&gt; #include &lt;string&gt; namespace SanProj { class SANPROJ_API Currency { public: Currency(); const std::string&amp; name(); const std::string&amp; code(); bool empty() const; protected: std::string name_; std::string code_; }; SANPROJ_API bool operator==(const Currency&amp;, const Currency&amp;); SANPROJ_API bool operator!=(const Currency&amp;, const Currency&amp;); SANPROJ_API std::ostream&amp; operator&lt;&lt;(std::ostream&amp; out, Currency&amp; c); } </code></pre> <p>And another header file with specific currencies:</p> <pre><code>// allccy.hpp namespace SanProj { class SANPROJ_API USDCurrency : public Currency { public: USDCurrency() { name_ = "American Dollar"; code_ = "USD"; } }; class SANPROJ_API CADCurrency : public Currency { public: CADCurrency() { name_ = "Canadian Dollar"; code_ = "CAD"; } }; } </code></pre> <p>The above classes form the contract of the DLL project. Now let's look at the client project files, which is a single class with <code>main</code> function:</p> <pre><code>#include "currency.hpp" #include "allccy.hpp" #include &lt;iostream&gt; using namespace SanProj; int main(int argc, char* argv[]) { USDCurrency uccy; std::cout &lt;&lt; uccy; } </code></pre> <p>Assuming all referencing/settings are already done in the Visual Studio project, I get the following error when trying to compile the client:</p> <pre><code>1&gt;testdll.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: __thiscall SanProj::USDCurrency::~USDCurrency(void)" (__imp_??1USDCurrency@SanProj@@QAE@XZ) 1&gt;testdll.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: __thiscall SanProj::USDCurrency::USDCurrency(void)" (__imp_??0USDCurrency@SanProj@@QAE@XZ) </code></pre> <p>Not surprisingly, this error goes away when I remove the <code>dllimport</code> part from the <code>SanProj.h</code> file and the executable is created.</p> <p>My question is, what's the point of the IDE generated <code>dllimport</code> if we can't compile clients against the header? Is there a way I can continue to use the header with both <code>dllimport</code> and <code>dllexports</code> and remove the linker errors? Also, why is it trying to resolve the symbol which has <code>dllimport</code> from the LIB file?</p> <p>TIA,<br> /sasuke</p> <p><strong>EDIT:</strong> Linker Command used by VisualStudio; as you can see, it has the LIB file.</p> <blockquote> <p>/OUT:"E:\vsprojects\SomeSln\Release\testdll.exe" /INCREMENTAL:NO /NOLOGO "E:\vsprojects\SomeSln\Release\SanProj.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" /MANIFEST /ManifestFile:"Release\testdll.exe.intermediate.manifest" /ALLOWISOLATION /MANIFESTUAC:"level='asInvoker' uiAccess='false'" /DEBUG /PDB:"E:\vsprojects\SomeSln\Release\testdll.pdb" /SUBSYSTEM:CONSOLE /OPT:REF /OPT:ICF /PGD:"E:\vsprojects\SomeSln\Release\testdll.pgd" /LTCG /TLBID:1 /DYNAMICBASE /NXCOMPAT /MACHINE:X86 /ERRORREPORT:QUEUE</p> </blockquote>
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    1. COAll you have to do is compile the DLL with `dllexport` and the client with `dllimport` *and provide the right library to the linker*. The error messages suggest that the linker is missing the library, and so can't actually link against the symbols (not a problem with the `import`/`export`).
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    2. COIt looks like you are not linking your executable to the import library created for your .dll.
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    3. CO@peachykeen: That's what I'm doing right now. I know the paths/configurations are good enough because removing the `dllimport` from the `SanProj.h` file successfully creates the executable. If it was an issue with linker not able to find the import lib, it should have complained even when I removed the `dllimport`, no?
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