Convert a Swift Array of String to a to a C string array pointer

Question

I\'m on Swift 3, and I need to interact with an C API, which accepts a NULL-terminated list of strings, for example

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Answer 1

You can proceed similarly as in How to pass an array of Swift strings to a C function taking a char ** parameter. It is a bit different because of the different const-ness of the argument array, and because there is a terminating nil (which must not be passed to strdup()).

This is how it should work:

let array: [String?] = ["name1", "name2", nil]

// Create [UnsafePointer]:
var cargs = array.map { $0.flatMap { UnsafePointer(strdup($0)) } }
// Call C function:
let result = command(&cargs)
// Free the duplicated strings:
for ptr in cargs { free(UnsafeMutablePointer(mutating: ptr)) }