I have an C struct (old library, blah blah blah) which contains an C string, now I need to convert CFString and Swift strings into this c string. Something like
struct Product{
char name[50];
char code[20];
}
So I'm trying to assign it as
productName.getCString(&myVarOfStructProduct.name, maxLength: 50, encoding: NSUTF8StringEncoding)
but the compiler is giving me the following error: cannot convert type (int8, int8, int8....) to [CChar].
A possible solution:
withUnsafeMutablePointer(&myVarOfStructProduct.name) {
strlcpy(UnsafeMutablePointer($0), productName, UInt(sizeofValue(myVarOfStructProduct.name)))
}
Inside the block, $0 is a (mutable) pointer to the tuple. This pointer is
converted to an UnsafeMutablePointer<Int8> as expected by the
BSD library function strlcpy().
It also uses the fact that the Swift string productName is automatically
to UnsafePointer<UInt8>
as explained in String value to UnsafePointer<UInt8> function parameter behavior. As mentioned in the comments in that
thread, this is done by creating a temporary UInt8 array (or sequence?).
So alternatively you could enumerate the UTF-8 bytes explicitly and put them
into the destination:
withUnsafeMutablePointer(&myVarOfStructProduct.name) {
tuplePtr -> Void in
var uint8Ptr = UnsafeMutablePointer<UInt8>(tuplePtr)
let size = sizeofValue(myVarOfStructProduct.name)
var idx = 0
if size == 0 { return } // C array has zero length.
for u in productName.utf8 {
if idx == size - 1 { break }
uint8Ptr[idx++] = u
}
uint8Ptr[idx] = 0 // NUL-terminate the C string in the array.
}
Yet another possible solution (with an intermediate NSData object):
withUnsafeMutablePointer(&myVarOfStructProduct.name) {
tuplePtr -> Void in
let tmp = productName + String(UnicodeScalar(0)) // Add NUL-termination
let data = tmp.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: true)!
data.getBytes(tuplePtr, length: sizeofValue(myVarOfStructProduct.name))
}
Update for Swift 3:
withUnsafeMutablePointer(to: &myVarOfStructProduct.name) {
$0.withMemoryRebound(to: Int8.self, capacity: MemoryLayout.size(ofValue: myVarOfStructProduct.name)) {
_ = strlcpy($0, productName, MemoryLayout.size(ofValue: myVarOfStructProduct.name))
}
}
