How to use C code in C++

Question

Just a small question: Can C++ use C header files in a program?

This might be a weird question, basically I need to use the source code from other program (made in C language) in a C++ one. Is there any difference between both header files in general? Maybe if I change some libraries... I hope you can help me.

Answer 1

Yes, you can include C headers in C++ code. It's normal to add this:

#ifdef __cplusplus extern "C" { #endif  // C header here  #ifdef __cplusplus } #endif 

so that the C++ compiler knows that function declarations etc. should be treated as C and not C++.

Answer 2

If you are compiling the C code together, as part of your project, with your C++ code, you should just need to include the header files as per usual, and use the C++ compiler mode to compile the code - however, some C code won't compile "cleanly" with a C++ compiler (e.g. use of malloc will need casting).

If on, the other hand, you have a library or some other code that isn't part of your project, then you do need to make sure the headers are marked as extern "C", otherwise C++ naming convention for the compiled names of functions will apply, which won't match the naming convention used by the C compiler.

There are two options here, either you edit the header file itself, adding

#ifdef __cplusplus  extern "C" { #endif  ... original content of headerfile goes here.   #ifdef __cplusplus  } #endif 

Or, if you haven't got the possibility to edit those headers, you can use this form:

#ifdef __cplusplus  extern "C" { #endif #include <c_header.h> #ifdef __cplusplus  } #endif