C + + calls to function

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There is a program, the code directory is as follows:

.
|--Calc
| |--calc.c
| '--calc.h
'--main.cpp

If main.cpp needs to call a function in Calc.h (CALC.C is C code)

After the traditional C programming requires # include "calc/calc.h", the function is declared and then called.

But since Main.cpp is a C + + code. The g++ compiler cannot compile by using the C-mode call.

Solution One:
If the amount of code in Calc is very small, or the code is written by itself can directly use C + + compatible with the characteristics of C, the CALC.C changed to Calc.cpp. can be compiled.

Solution Two:
At the top of each function in calc.h, add: extern "C"

The simpler scenario is:

extern " C " {     void fun1 (int  arg1);      void fun2 (intint  arg2);      void fun3 (intint int arg3);}

If you are not sure whether the current compilation environment is C or C + +, you can:

extern " C " {#endifvoid fun1 (intvoid fun2 (intint)    void fun3 (int int int arg3); #ifdef __cplusplus}    #endif

Workaround Three:
What if someone else has written a header file that we can't modify? Rewrite a header file that is specifically used by C + +.

Example: Writing a header file cpp_calc.h

extern " C "  "calc.h";}

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C + + calls to function