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

[J Decker]

Or make c++ wrappers that use dlopen/dlsym or loadlibrary/getprocaddress as
appropriate and reference the libs through an interface class.

On Fri, Jun 5, 2015 at 7:44 PM, J Decker <d3ck0r at gmail.com> wrote:

> it's not the lib, it's the header interface to the lib.
>
> On Fri, Jun 5, 2015 at 7:42 PM, Sunrise <helios.corona at gmail.com> wrote:
>
>>  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> 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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>>
>>
>>
>
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