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Using C++ within C implementation

This is a discussion on Using C++ within C implementation within the C Programming forums, part of the General Programming Boards category; I'm required to "transfer" my c++ implementation as an addition to already existing c code. The main problem are the ...

  1. #1
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    Using C++ within C implementation

    I'm required to "transfer" my c++ implementation as an addition to already existing c code. The main problem are the structures that I use in c++, and that are not recognized by c. For instance, the struct
    Code:
    struct Matrix {
            std::vector<double> mat;
            unsigned int rowNo;
            unsigned int colNo;
    };
    has a std::vector member. My c++ is largely relying on the above struct, but also on
    std::vectors. What is your suggestion on most efficient transition?
    It would be very good if I could somehow declare the structures that I use in C++, in C, and then simply copy methods.

    Thanks.

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    You will have to implement you own vector type in C, there is no other way without using an external library.
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    Thanks for the message.

    What external library should I use to facilitate the work?
    I suppose the std:: preceding vector would fit withing the library environment.

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    You seem not to understand that C and C++ are two separate languages.

    Most C++ compilers can deal with C code.
    But, to a C compiler C++ might as well be Klingon Secret Code for all it will understand of it.

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    I understand that.

    But, hauzer suggest that by importing certain library in C I might utilize my C++ code.
    Anyway, what is your suggestion?

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    Perhaps (and I know almost zip about C++), allocate a C array set to the same size as your vector, and transfer all contents from the vector to the array.

    Or can you just treat the vector as an array, with some restrictions?

  7. #7
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by onako
    But, hauzer suggest that by importing certain library in C I might utilize my C++ code.
    Yeah, that library is your own C++ library, but with a C interface wrapper that is declared extern "C".
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    Thanks!
    Could you provide me with the minimal working example, i.e. the content of .h, .cpp and .c files that I might use as the development base.
    I tried C wrapping of C++ code example, but get the error:

    In file included from source.c:1:
    header.h:2: error: expected identifier or ( before string constant

    What might be the problem?

  9. #9
    C++ Witch laserlight's Avatar
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    Code:
    #ifndef __cplusplus
    should be:
    Code:
    #ifdef __cplusplus
    Also, unless you are compiling with respect to C99, the // style comment should be replaced with a /* */ style comment.
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    Quote Originally Posted by laserlight View Post
    Code:
    #ifndef __cplusplus
    should be:
    Code:
    #ifdef __cplusplus
    Also, unless you are compiling with respect to C99, the // style comment should be replaced with a /* */ style comment.
    Done that! Now, it complains about the actual function:

    /tmp/cccMKk1q.o: In function `main':
    source.c.text+0xa): undefined reference to `func'
    collect2: ld returned 1 exit status

  11. #11
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    You forgot to link the object file generated by the C++ compiler to your C executable program.
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    Given the file content as defined above, what is the exact sequence of commands I should use to make it work?


    gcc -c source.c
    gcc -c source.cpp // well, same file name
    gcc source.o source.o -o myprog
    //// the above is inappropriate

  13. #13
    C++ Witch laserlight's Avatar
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    You could use:
    Code:
    g++ -c source.cpp
    gcc source.c source.o -o myprog
    If you really want to compile each source file separately from linking, then use -o to specify different output filenames, e.g.,
    Code:
    gcc -c source.c -o source_c.o
    g++ -c source.cpp -o source_cpp.o
    gcc source_c.o source_cpp.o -o myprog
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    Quote Originally Posted by laserlight View Post
    You could use:
    Code:
    g++ -c source.cpp
    gcc source.c source.o -o myprog
    If you really want to compile each source file separately from linking, then use -o to specify different output filenames, e.g.,
    Code:
    gcc -c source.c -o source_c.o
    g++ -c source.cpp -o source_cpp.o
    gcc source_c.o source_cpp.o -o myprog
    First option produced the following:
    source.o: In function `func':
    source.cpp.text+0xa): undefined reference to `std::cout'
    source.cpp.text+0xf): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std:perator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)'
    source.cpp.text+0x14): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::endl<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&)'
    source.cpp.text+0x1c): undefined reference to `std::basic_ostream<char, std::char_traits<char> >:perator<<(std::basic_ostream<char, std::char_traits<char> >& (*)(std::basic_ostream<char, std::char_traits<char> >&))'
    source.o: In function `__static_initialization_and_destruction_0(int, int)':
    source.cpp.text+0x45): undefined reference to `std::ios_base::Init::Init()'
    source.cpp.text+0x4a): undefined reference to `std::ios_base::Init::~Init()'
    source.o.eh_frame+0x12): undefined reference to `__gxx_personality_v0'
    collect2: ld returned 1 exit status

  15. #15
    C++ Witch laserlight's Avatar
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    Ah, you need to link the C++ runtime too, and I am not sure how to do that. One way out, if feasible, is to write a C++ wrapper for your main function (i.e., rename your main function, and call it from a C++ source file that contains the new main function), then rely on the C++ compiler linking the C++ runtime for you.
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