How can I call a non-system C function f(int,char,float) from my C++ code?, C++ FAQ

C++ FAQ / Section 32 / FAQ 32.5

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?

[32.5] How can I call a non-system C function f(int,char,float) from my C++ code?

If you have an individual C function that you want to call, and for some reason you don't have or don't want to #include a C header file in which that function is declared, you can declare the individual C function in your C++ code using the extern "C" syntax. Naturally you need to use the full function prototype:

extern "C" void f(int i, char c, float x);

A block of several C functions can be grouped via braces:

extern "C" {
  void   f(int i, char c, float x);
  int    g(char* s, char const* s2);
  double sqrtOfSumOfSquares(double a, double b);
}

After this you simply call the function just as if it were a C++ function:

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