How to use C++ in Go with the C_wrapper function

The calling of C++ in Go is not as straight forward as it is in C. It requires more work to run C++ in Go. There are two ways to run C++ in Go:

• Using the C_wrapper function
• Using SWIGSWIG is used to generate the c_wrapper function for C++ to call in Go.

In this answer, we implement a C++ class and write a C wrapper function to perform the sum of two numbers.

Steps

We perform the following steps:

1. Create a header file sum.hxx and paste the code below:

   #ifndef SUM_H
   #define SUM_H
   class SumClass { 
   //create class
   public:
     int Sum(int a, int b); //declare function
   };
   #endif
   

2. Create a file sum.cxx and paste the code below:

   #include "sum.hxx"
   #include <math.h>
   #include <iostream>
   int SumClass::Sum(int a,int b) {
     std::cout << "C++ says: Sum from Sum funct(" << a << "," << b
       << "), and Sum is:(" << a+b << ")" << std::endl;
     return (a+b);
   }
   

3. Create a header file wrap_sum.hxx and paste the code below:

   #ifndef WRAP_SUM_H
   #define WRAP_SUM_H
   
   // __cplusplus tells the compiler that inside code is compiled with the c++ compiler
   #ifdef __cplusplus
   // extern "C" tells C++ compiler exports the symbols without a name manging.
   extern "C" {
     #endif
     int sum_from_cplus(int a,int b); //declare wrapper function
     #ifdef __cplusplus
   }
   #endif
   #endif
   

4. Create a file wrap_sum.cxx and paste the code below.

   #include "wrap_sum.hxx"
   #include "sum.hxx"
   
   int sum_from_cplus(int a, int b) {
     SumClass num; //create object of class SumClass
     return num.Sum(a, b); // Call Sum function using wrapper function sum_from_cplus
   }
   

5. Create a file main.go and paste the code below:

   package main
   // #include "wrap_sum.hxx"
   import "C"
   import "fmt"
   
   func main() {
   
     a := 5
     b := 10
     sum := C.sum_from_cplus(C.int(a), C.int(b))
     fmt.Printf("Go has result, sum is: %v\n", sum)
   }
   

6. Run the go build executable file that will be generated. Run executable file ./<execute_name>.

Code

Let’s run the above code in the playground below:

Output

We can expect the following output:

C++ says: Hello to Go!!!! 
Go has result, sum is: 15