How to Pass Go Slices to C Functions and Handle Pointer Modifications?

Passing Pointers to Slices to C Functions in Go

When calling C functions from Go using cgo, it can be challenging to pass pointers to slices. Consider a C function like:

int f(int *count, char ***strs);

where count is the length of the strs array, strs is an array of strings, and the return value indicates an error status.

In Go, one might initially attempt to pass count and strs as follows:

C.f((*C.int)(&count), (**C.char)(&strs[0]))

However, this won't allow modifications to strs in C. To enable this, it's necessary to allocate the array in C. Similar to C.CString, it's essential to keep track of where to free the outer array, especially when the C function potentially allocates a new array.

The code below demonstrates how to allocate the C array:

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

// Convert the C array to a Go array for indexing
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)))

In this code, cArray is allocated in C, a is a slice wrapper around this array to allow indexing, and each string is copied into C memory. The function f can now modify strs in C and return the modified value back to Go.

The above is the detailed content of How to Pass Go Slices to C Functions and Handle Pointer Modifications?. For more information, please follow other related articles on the PHP Chinese website!