Thread: combining c with c++ code

To access a function written in C from C++, you just have to put extern "C" around the function. That's it basically.

Code:

extern "C" void function() {}

You can use extern "C" with curly braces to enclose a number of functions.

If the code was written to support C++, it might have something like this in the header file(s):

Code:

/* at the beginning of the file */
#ifdef __cplusplus
extern "C" {
#endif

/* ... the function declarations ... */

#ifdef __cplusplus
}
#endif

If not, you can add that yourself, or do it in your C++ code where you include the header file.

Code:

extern "C" {
#include "header.h"
}

You should then be able to include the .c files in your project and compile them normally. (A C++ compiler will likely be able to compile the C code.)

Hi I downloaded c code that I am now using in my c++ plugin code.
I managed to tie both c and c++ code using the extern "C"{} construct.

I am getting these error messages. There is a main proc in every c file and I think that is confusing my compiler. Does anyone know how to resolve this error message?

------ Build started: Project: compCal, Configuration: Debug Win32 ------
Linking...
cal_fo.obj : error LNK2005: _main already defined in cal.obj
csyn.obj : error LNK2005: _main already defined in cal.obj
ecal.obj : error LNK2005: _main already defined in cal.obj
ic2wc.obj : error LNK2005: _main already defined in cal.obj
ncal.obj : error LNK2005: _main already defined in cal.obj
ncal_fo.obj : error LNK2005: _main already defined in cal.obj
ncsyn.obj : error LNK2005: _cc_generate_calibration_constants already defined in csyn.obj
ncsyn.obj : error LNK2005: _nc_generate_calibration_constants already defined in csyn.obj
ncsyn.obj : error LNK2005: _generate_calibration_data already defined in csyn.obj
ncsyn.obj : error LNK2005: _main already defined in cal.obj
ncsyn.obj : error LNK2005: _idum already defined in csyn.obj
wc2ic.obj : error LNK2005: _main already defined in cal.obj
xfd2xfu.obj : error LNK2005: _main already defined in cal.obj
Creating library Debug/compCal.lib and object Debug/compCal.exp
cal_main.obj : error LNK2019: unresolved external symbol _lmdif_ referenced in function _cc_compute_exact_f_and_Tz
ecalmain.obj : error LNK2001: unresolved external symbol _lmdif_
Debug\compCal.dll : fatal error LNK1120: 1 unresolved externals

tim

Umm . . . you can't compile a bunch of files each with a main() and expect it to work, as you have seen.

If you're sure that the code will actually work together -- which I highly doubt -- you could try remaining the main() functions in each of the files and somehow creating a main() of your own which calls all of those functions. But that would execute each one sequentially, which may not be what you want.

I guess the short answer is, rename the main() functions to something else. Whether you'll actually be able to use the resulting code is another matter.