Calling C from Go #1

README.md

Calling C from Go

Put all files in ctest directory.

Run test

cd ctest
go test

ctest.c

#include <stdio.h>
#include <string.h>

#include "ctest.h"

void c_call(void *in, int lin, void *out, int *lout)
{
    char *ain = (char*) in;
    char *aout = (char*) out;
        
    printf("C: c_call with: '%s', %d bytes\n", ain, lin);
    int j = 0;
    for (int i = 0; i < lin; i++) {
        char c = ain[i];
        if (i < (lin-1)) {
            if (c == 'G' && ain[i+1] == 'o') {
                c = 'C';
                i++;
            }
        }
        aout[j] = c;
        j++;
    }
    *lout = j;
    printf("C: all done");
}

ctest.go

package ctest

/*

#include "ctest.h"

void c_call(void*, int, void* , int*);
*/
import "C"

import (
	"fmt"
	"reflect"
	"unsafe"
)

func CallCFunc(input []byte) []byte {
	var inputLength int = len(input)
	const MAX_OUTPUT int = 10
	var output []byte = make([]byte, MAX_OUTPUT)

	// Conversion to C types
	var inPtr unsafe.Pointer = unsafe.Pointer(&input[0])
	var inL C.int = C.int(inputLength)
	var outPtr unsafe.Pointer = unsafe.Pointer(&output[0])
	var outL C.int = C.int(0)

	// Call the C function
	defer func() {
		p := recover()
		if p != nil {
			fmt.Printf("Panic with %s: %s\n", reflect.TypeOf(p).String(), p)
		}
	}()
	C.c_call(inPtr, inL, outPtr, &outL)

	// Copy the result to a new buffer
	var length int = int(outL)
	res := append([]byte{}, output[:length]...)

	// Return result
	return res
}

ctest.h

#ifndef CTEST_H
#define CTEST_H
void c_call(void*, int, void* , int*);

#endif

ctest_test.go

package ctest

import (
	"github.com/stretchr/testify/assert"
	"testing"
)

func TestCCall(t *testing.T) {
	var result []byte = CallCFunc([]byte("Hello Go!"))
	assert.Equal(t, "Hello C!", string(result))
}

func TestCCallArrayOverflow(t *testing.T) {
	var result []byte = CallCFunc([]byte("Hello, hello Go!"))
	assert.Equal(t, 0, len(result))
}