Compiling C99 files with C++ compiler

Question

Have not found the exact question i am asking in either google or here, everything talks about wanting to call c++ from c code or some part being compiled with c compiler and some other with c++ and then later linked together and the problems that arise from that which i do not want.

I want to compile and link C99 files with C++ compiler of Visual Studio in my all C++ application and be able to call the c functions without errors and problems.There will be no c linker involved or compiling some part with different compilers and linking together later, or any kind of trick. The headers are from C library (libcurl) and some others as i want to use them in my application. I do not want to use the C++ bindings i want to compile c code as c++. Can i trust c code be compiled as C++ code without major refactoring? What to do differently than when including C++ headers? What incompatibilities to expect?

Answer 1

C and C++ are two different, but closely related, languages. C++ is nearly a superset of C++, but not quite (in particular, C++ has keywords that C lacks).

If your code depends on C99 features (i.e., features that are in C99 but not in C90), then you may be out of luck. Microsoft's C compiler does not support C99 (except for a few minor features; I think it permits // comments), and Microsoft has stated clearly that such support is not a priority. You may be able to modify the code so it's valid C90, depending on what features it uses.

Microsoft Visual Studio supports compiling both C and C++ (though it tends to emphasize C++). If you can get your C code compiling with the MS C compiler, I suggest doing just that rather than treating it as C++. C++ has features, particularly extern "C", that are specifically designed to let you interface C and C++ code. The C++ FAQ Lite discusses this in section 32.

If you really need to compile your C code as C++ for some reason, you can probably do so with a few minor source changes. Rename the source file from foo.c to foo.cpp, compile it, and fix any errors that are reported. The result probably won't be good C++, but you should be able to get it to work. There are a few constructs that are valid C and valid C++ with different semantics, but there aren't many of them, and you're not likely to run into them (but you should definitely keep that in mind).

If you want to continue maintaining the code as C++, my advice is to go ahead and make the changes needed to do that, and then stop thinking of it as C code.

The actual need to compile the same code both as C and as C++ is quite rare. (P.J. Plauger, for example, needs to do this, since he provides some libraries intended to be used in either language.) In most cases, C++'s extern "C" and other features are good enough to let you mix the two languages reasonably cleanly.

Answer 2

In theory, C code should be able to be compiled as C++ code. At some point Dr.Stroustrup made the point that all code from ANSI C edition of the K&R compiles with a C++ compiler and has the same semantics as the code compiled with a C compiler has (this was construed that all ANSI C code would be valid C++ code which is, obviously, not the case, e.g., because many C++ keywords are not reserved identifiers in C).

However, certain idioms in C will require substantial changes to the C code if you want to compile the code with a C++ compiler. A typical example is the need to cast void* to the proper type in C++ which isn't needed in C and it seems it is frowned upon casting the result from malloc() to the proper pointer type although the effect is that it prevents the C code from being compiled with a C++ compiler (in my opinion a good think, e.g., because there the tighter rules may result in discovering problems in the C code even if the production version is being compiled with a C compiler). There are also a few subtle semantic differences as far as I know, although right now I can't easily pin-point one of them. That is, the same code compiled with a C and a C++ compiler may have defined but different results for both cases.

In practice, I doubt that you can simply compile a non-trivial body of C code with a C++ compiler and get a program which behaves the same as the original C code. If the C program you envision to compile with a C++ comes with a thorough set of test cases it may be feasible to port the code to C++ but it will involve more work than merely renaming the file from <name>.c to <name>.cpp. I could imagine that a tool could do the required conversions (a compiler compiling C source to C++ source) but I'm not aware of a such a tool. I'm only aware of the opposite direction yielding entirely unreadable code (for example Comeau C++ uses C as a form of portable assembler).

Answer 3

If you want to do this using visual studio, then it is not possible. MSVC doesn't support C99.