How Can I Pass a Go Slice to a C Function That Expects a Pointer to an Array of C Strings?

Passing a Pointer to a Slice to a C Function in Go

In Go, a common task when interacting with C functions is passing complex data structures such as slices. However, Go slices and C arrays have fundamental differences that require special handling.

Consider the following C function with the signature int f(int *count, char ***strs). It takes two pointers: count points to the length of an array of strings, and strs points to an array of string pointers.

In Go, we can't directly pass a slice to such a function because slices are a Go-specific data structure and differ from C arrays. Additionally, Go slices contain a Go pointer, which cgo prohibits passing to C functions.

To overcome this, we need to allocate the array in C manually and track where to free the outer array. For each string in the Go slice, we convert it to a C string using C.CString and record the corresponding C string pointers in the allocated C array.

Here's a modified version of the Go code:

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

// Convert the C array to a Go Array for easy indexing
a := (*[1<p>This approach ensures that the C function has access to a manipulatable C array, while allowing us to convert the manipulated array back into a Go slice for further use.</p>

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