CODEWITHSUNDEEP
c++staticnamespaces
Sania Programmer
Sania Programmer

Reputation: 264

Conflict resolution using multiple static libraries in C++

I have 2 static libraries from «vendor1» and «vendor2»:

In the file, vendor1.h. The following declaration is there:

double Min();

In the file, vendor2.h. The following declaration is there:

double Min();

In my client file:

include "vendor1.h"  
include "vendor2.h"  
double x = Min();

It by defaults calls vendor1.h. I tried introducing the namespace:

   namespace vendor1 {  
    include "vendor1.h"
   }

   namespace vendor2 {  
    include "vendor2.h"
   }

A call to the following function

double xx = vendor2::Min();

I get the following linker errors:

Client.cpp 1>Client.obj : error LNK2019: unresolved external symbol "double __cdecl vendor2::Min(void)" (?Min@vendor2@@YANXZ) referenced in function _wmain 1>c:\temp\Client\Debug\Client.exe : fatal error LNK1120: 1 unresolved externals

How can I fix this without creating wrappers for each of the wrappers?

Upvotes: 3

Views: 4630

Answers (2)

Sergey Vyacheslavovich Brunov
Sergey Vyacheslavovich Brunov

Reputation: 18116

How about wrapping the functions into different namespaces?

vendor1_wrapper.h:

namespace vendor1 {
    double Min();
}

vendor1_wrapper.cpp:

#include "vendor1_wrapper.h"
#include "vendor1.h"

namespace vendor1 {
    double Min()
    {
        return Min();
    }
}

vendor2_wrapper.h:

namespace vendor2 {
    double Min();
}

vendor2_wrapper.cpp:

#include "vendor2_wrapper.h"
#include "vendor2.h"

namespace vendor2 {
    double Min()
    {
        return Min();
    }
}

Now you can use the functions using namespaces (your client file):

#include "vendor1_wrapper.h"
#include "vendor2_wrapper.h"

...

vendor1::Min();
vendor2::Min();

Upvotes: 1

Dietmar Kühl
Dietmar Kühl

Reputation: 154005

If you have two static libraries with conflicting names you won't be able to link your program statically! The static linker will just go and find the first symbol matching an undefined symbol and choose this. Wrapping the names into a namespace doesn't help: this changes the namespace being expected in the library. You just found why namespace are a good thing.

How to solve the problem? I'm not aware of an approach which is based on the C++ standard. Practically, you may be able to do something: create a dynamic library which forwards to your conflicting functions but puts the name into separate namespaces (or uses different names). The dynamic libraries are linked with individual static libraries, i.e. the conflict doesn't happen at this time. You will probably also need to avoid the underlying names being visible from the symbols in the shared library. The details on how this is done depend on the compiler and I don't know who to deal with MSVC++ for things like this.

Upvotes: 2

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