How to pass pointer to slice to C function in go

Question

Background: using cgo to call C functions from Golang.

I want to use a C function which has this signature: int f(int *count, char ***strs). It will mod

Answer 1

A Go slice is both allocated in Go, and a different data structure than a C array, so you can't pass it to a C function (cgo will also prevent you from doing this because a slice contains a Go pointer)

You need to allocate the array in C in order to manipulate the array in C. Just like with C.CString, you will also need to track where to free the outer array, especially if the C function may possibly allocate a new array.

cArray := C.malloc(C.size_t(c_count) * C.size_t(unsafe.Sizeof(uintptr(0))))

// convert the C array to a Go Array so we can index it
a := (*[1<<30 - 1]*C.char)(cArray)
for index, value := range strs {
    a[index] = C.CString(value)
}

err := C.f(&c_count, (***C.char)(unsafe.Pointer(&cArray)))