integrate a C and C++ program

Question

I am trying to control a drone using image processing. The image capture from the drone is an opencv C++ program. The drone control program is C program. Now I want to integrate both the programs so that I run a single program by which I can get both images and control the drone. How do I do that? My C program is a socket program to send commands to drone and the C++ program to capture image stream from drone from a tcp socket. Is there any way to do it or should I convert one whole program into another language? Anyone help.

regards, shiksha

You'll probably need to either merge both programs into one program in one language or turn one (or both) of the programs into a DLL. — cf-, Mar 10 '14 at 03:45
I would compile the C program as a static lib and link it to the C++ code. To access C++ code from C, use extern "C" in the header. Don't allow any unhandled exceptions from C++ functions callable from C. You can also probably just port the C code to C++ with little effort. — VoidStar, Mar 10 '14 at 03:49
Why do you need a single program? At what point do these two independent pieces of functionality need to communicate? — CB Bailey, Mar 10 '14 at 06:32
i want the image grabbing an control parameters in a loop. the control parameters are fed back to stabilise the system. so i want both the programs to run in the same loop. — wireless_lab, Mar 10 '14 at 11:03

score 3 · Answer 1 · answered Mar 10 '14 at 04:00

3

You have a number of options. The easiest may be to simply rename your *.c files to *.cpp - they may compile directly in C++. You may then have some issues linking with external libraries that were built using a C compiler. These linking issues can often be resolved by guarding each header include with

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

If this isn't feasible (e.g. if your C project consists of a lot of files, or you want to keep compiling in C), you may want to build the C part as a static library and link it with your C++ program. You could go in the other direction - build your C++ component as a static library and link it with the C program. The downside to this is that you would have to write a C wrapper for your C++ code which could take some effort (or be impossible, depending on which features of C++ you use in your API). Care must be taken to ensure the wrapper is linked as C so that the symbols will be compatible with what C produces.

answered Mar 10 '14 at 04:00

Chris McGrath

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System libraries generally are already protected like that. – vonbrand Mar 10 '14 at 04:02
That is true, but user-written libraries aren't always protected. It's something to be mindful of nonetheless. Particularly if his code is being run on an embedded system with sloppily written headers. – Chris McGrath Mar 10 '14 at 04:05
thanks for the reply. i converted my c code to cpp program. it executes fine. but when i combine both the programs it is giving a lot of errors like template with c linkage – wireless_lab Mar 10 '14 at 05:44
That sounds like you're trying to compile some code which uses the C++ feature templates but are telling the compiler to use C linkage with the extern "C" trick. This post discusses it: http://stackoverflow.com/questions/4877705/why-cant-templates-be-within-extern-c-blocks - I'd suggest seeing if you can avoid that feature in the header. – Chris McGrath Mar 10 '14 at 06:05

Spock77 · Answer 2 · 2014-03-10T04:29:10.447

Using C libs in C++ programs is a common way to reuse the functionality. These languages can be built together. Usually C++ code calls C- module API which provide required functions.

In such case you can just add C files into the C++ project and build a single executable.

You only should consider the different linkage in C and C++. C function declarations should be compiled with extern "C" standard linkage specification. C-libraries usually already have such code in the headers (if not - add it):

#ifdef __cplusplus
    extern "C" { 
#endif

and in the end of the file

#ifdef __cplusplus
    }
#endif

extern "C" prevents changing function names by C++ compiler. As C++ supports overloading, C++ compiler adds information about function parameters into the function name, so called name mangling. This should not be done for C-library code.

integrate a C and C++ program

2 Answers2