gcc: Linking C library in a C++ app results in "multiple definition of" errors

I have a working C library which I want to link to a C++ application using gcc but the linker (g++) is giving me the "multiple definition" error. With a C application and gcc it works. The headers defining the interface all contain the:

#ifdef __cplusplus 
extern "C" {
#endif

I checked the library using the "nm" command and it does have multiple definitions of the me开发者_开发知识库thod (the method in question is not from the public interface).

My questions are:

1. Why does my library have multiple definitions (some have the T while others have U)?

2. Why it works if the application including the file is a C application (I'm using -Wall to build)?

3. Do I need any special attribute or use a specific file extension to make it work or is the case that I need to go back to programming school :) ?

Paying more attention to the lib.a file I can see that one of the objects is included twice. For example, I have two sections for the same object:

 obj1.o
 00000000     T    Method

 obj2.o
 00000000     T    Hello

 obj1.o
 00000000     T    Method

I guess this is the problem?

Any help is really appreciated.

My wild guess is that the "#define BLAHBLAH_H" and "#ifndef BLAHBLAH_H / #endif" set outside the 'extern "C"{}' thing.

after playing around I found that actually the whole command line (it's kind of a complex application with an automated compilation and linkage) contained the --whole-archive parameter before the inclusion of the C library. Moving the library after the --no-whole-archive fixed the problem.

Original command

   gcc -Wl,**--whole-archive** -l:otherlibs *-Llibpath -l:libname* Wl,**--no-whole-archive** -o myApp hello.c

Fixed command

   gcc -Wl,**--whole-archive** -l:otherlibs Wl,**--no-whole-archive** *-Llibpath -l:libname* -o myApp hello.c

Thank you for everyone's help guys and sorry if I didn't provide enough/accurate information.

Best Regards