How can I include a non-system C header file in my C++ code?, C++ FAQ

C++ FAQ / Section 32 / FAQ 32.3

Section 32:

32.1	What do I need to know when mixing C and C++ code?
32.2	How can I include a standard C header file in my C++ code?
32.3	How can I include a non-system C header file in my C++ code?
32.4	How can I modify my own C header files so it's easier to `#include` them in C++ code?
32.5	How can I call a non-system C function `f(int,char,float)` from my C++ code?
32.6	How can I create a C++ function `f(int,char,float)` that is callable by my C code?
32.7	Why is the linker giving errors for C/C++ functions being called from C++/C functions?
32.8	How can I pass an object of a C++ `class` to/from a C function?
32.9	Can my C function directly access data in an object of a C++ `class`?
32.10	Why do I feel like I'm "further from the machine" in C++ as opposed to C?

[32.3] How can I include a non-system C header file in my C++ code?

If you are including a C header file that isn't provided by the system, you may need to wrap the #include line in an extern "C" { /*...*/ } construct. This tells the C++ compiler that the functions declared in the header file are C functions.

// This is C++ code

extern "C" {
  // Get declaration for f(int i, char c, float x)
  #include "my-C-code.h"
}

int main()
{
  f(7, 'x', 3.14);   // Note: nothing unusual in the call
  ...
}

Note: Somewhat different guidelines apply for C headers provided by the system (such as <cstdio>) and for C headers that you can change.