How to Pass a Go Slice to a C Function that Modifies a Pointer to a Pointer to an Array of Strings?

Passing a Pointer to Slice to a C Function in Go

Problem

When calling a C function that expects a pointer to a pointer to an array of strings, how can this be achieved in Go while also allowing the C function to modify the string array?

Solution

Creating a slice in Go and passing it directly to a C function is not possible due to differences in data structures and memory allocation. Instead, it is necessary to allocate the array in C.

// Allocate an array in C
cArray := C.malloc(C.size_t(c_count) * C.size_t(unsafe.Sizeof(uintptr(0))))

// Convert C array to Go array
a := (*[1<<30 - 1]*C.char)(cArray)

// Copy Go strings to C array
for index, value := range strs {
    a[index] = C.CString(value)
}

// Call C function with pointer to array pointer
err := C.f(&c_count, (***C.char)(unsafe.Pointer(&cArray)))

By allocating the array in C, it allows the C function to modify and resize the array. The changes made in C will be reflected in the Go slice after the C function returns.

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