How to convert from [][]byte to **char in go

Question

I would like to convert from a go [][]byte to a C **char. In other words, I have a byte matrix in go that I would like to convert to a char double pointer in C.

Please assume that I HAVE to have a [][]byte as input and a **char as output.

I know it is possible to convert from []byte to *char by doing something like:

((*C.char)(unsafe.Pointer(&data[0])))

But it does not seem possible to extend this case into the second dimension. I have tried something pretty elaborate, where I pack a [][]byte into a new []byte. I then send that []byte to a C function that creates a **char using pointer arithmetic to point into the new []byte at the correct locations.

This conversion is giving me strange behaviour though, where my data would be correct for a few iterations, but gets corrupted seemingly between function calls.

If anyone has any ideas, I would really appreciate it.

From the responses I see it is also important to state that I'm working with raw data and not strings. Hence the go byte type. The original data would, therefore, be corrupted if C string terminators are added. I'm just using C **char, because a char is one byte in size. That said, thanks for the responses. I was able to adapt the accepted answer for my needs.

Answer 1

Untested skeleton:

func foo(b [][]byte) {
        outer := make([]*C.char, len(b)+1)
        for i, inner := range b {
                outer[i] = C.CString(string(inner))
        }
        C.bar(unsafe.Pointer(&outer[0])) // void bar(**char) {...}
}

EDIT: Full example (tested):

package main

/*
#include <stdlib.h>
#include <stdio.h>

void bar(char **a) {
        char *s        ;
        for (;(s = *a++);)
                printf("\"%s\"\n", s);
}
*/
import "C"
import "unsafe"

func foo(b [][]byte) {
        outer := make([]*C.char, len(b)+1)
        for i, inner := range b {
                outer[i] = C.CString(string(inner))
        }
        C.bar((**C.char)(unsafe.Pointer(&outer[0]))) // void bar(**char) {...}
}

func main() {
        foo([][]byte{[]byte("Hello"), []byte("world")})
}

---

(15:24) jnml@fsc-r550:~/src/tmp/SO/14833531$ go run main.go 
"Hello"
"world"
(15:25) jnml@fsc-r550:~/src/tmp/SO/14833531$