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I am working on a VS 2012 project and i am using an already compiled static library (that was compiled in VS 2013). The library references the "vacopy" method that is VS 2013 compatible but not found in VS 2012.

When I compile my cpp project, I get the linking error : error LNK2019: unresolved symbol __imp___vacopy

My first reflex was to add the declaration and definition of va_copy in my project, so I included the following:

in a header file : 

void va_copy(va_list dest, va_list src);

in a cpp file : 

void va_copy(va_list dest,va_list src)
{
   dest = src;
}

But this didn't resolve the problem, I still get the same linking error.

Thanks in advance for your answers.

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You basic problem is that the library was compiled to link with standard libraries in a DLL (thus the __imp__); you application is probably set differently (to grab standard calls from a statically linked in library).

You either have to match your compiler settings (in this case project properties -> C/C++ -> Code Generation section) where you can specify to use DLL or static options.

It's often worth checking if there is a way to specify to the include files which version of the link you need - some libraries (CURL for example) allow you to define compiler predefines to control exactly which functions are linked to.

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Thank you for your answer. I checked the compilation settings for the library and you are right : the library was compiled to link with standard libraries in a DLL. I also checked my application's settings and they are the same as the library: they both use DLL options.
The other thing you can mess with is the 'platform toolset' setting but I assume that 2012 doesn't have installed tools for 2013 and although these can be installed I believe this gets quite tricky. A mismatch in debug/release versions can also be an issue I think
Also in my experience you need to do a full clean+rebuild because VS is not so good with dependancies when you change the config settings
I cleaned then rebuilt the project but the problem is still there. I guess it is (and correct me if i'am wrong) because the library expects the function "va_copy" to be dll exported (since it has been compiled in windows). Which is not the case in my definition above, not sure about that though.

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