[CMake] undefined reference to error when use "c" extension

[Sunrise]

Thanks for your reply. I am aware of extern "C" {} but this is not an 
option for me. As I mentioned, there are a lot of lib files (which were 
not written by me) and I was wondering if lib itself could be untouched.

On 06/05/2015 07:33 PM, J Decker wrote:
> c++ does name mangling on functions... so functions like 'f' become a 
> much more complex name (as shown in the xxx not found in your error 
> messages).
> In order for C++ to not produce a mangled name C functions have to be 
> defined as
>
> extern "c" void f( void );
> but 'extern "c"' is not liked by C... so you really need to define in 
> the shared header something like...
>
> #ifdef __cplusplus
> #define CEXTERN extern "C"
> #ese
> #define CEXTERN
> #endif
>
> CEXTERN void f( void );
>
> But of course since you don't know about name mangling I guess you 
> don't know proper header usage either.  This is not a cmake issue, but 
> a general C++ issue... and you'd do better asking stack exchange or 
> something.
>
> On Fri, Jun 5, 2015 at 6:37 PM, Sunrise <helios.corona at gmail.com 
> <mailto:helios.corona at gmail.com>> wrote:
>
>     Hello,
>
>     I am linking my code to a library. My code is in C++ but the
>     library is in C.
>
>     The problem is that whenever the extension of library
>     implementations are "c" (not cpp), they are not linked and I get
>     "undefined reference to" error.
>
>     Here is an example:
>
>     Suppose I have
>     ./src/main.cpp // as main file
>     ./include/lib.h
>     ./include/lib.c // as a library
>
>     And the cmake file is
>
>     cmake_minimum_required(VERSION 2.8)
>     project(myproj)
>
>     set(INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/include)
>     include_directories(${INCLUDE_DIR})
>     add_library(MY_LIB ${INCLUDE_DIR}/Lib.c)
>
>     set(EXECUTABLE_NAME "myproj")
>     set(SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/src)
>     add_executable(myproj ${SOURCE_DIR}/main.cpp)
>
>     target_link_libraries(myproj MY_LIB)
>
>     This returns undefined reference to error, but if I rename lib.c
>     to lib.cpp, everything works fine.
>
>     How can I resolve this? I do not want to rename the file to cpp,
>     because there are a lot of library files and I prefer to keep the
>     library implementations untouched.
>
>     Thanks.
>
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