Convert String to int8 array
I have a C struct (old library, blah blah blah) that contains a C string, now I need to convert the CFString and Swift to this c string. Something like
struct Product{
char name[50];
char code[20];
}
So I am trying to assign it as
productName.getCString(&myVarOfStructProduct.name, maxLength: 50, encoding: NSUTF8StringEncoding)
but the compiler gives me the following error: Cannot convert type (int8, int8, int8 ....) to [CChar].
source to share
Possible Solution:
withUnsafeMutablePointer(&myVarOfStructProduct.name) {
strlcpy(UnsafeMutablePointer($0), productName, UInt(sizeofValue(myVarOfStructProduct.name)))
}
Inside a block, $0
is a (mutable) pointer to a tuple. This pointer is converted to UnsafeMutablePointer<Int8>
, as expected
BSD Library Functionstrlcpy()
.
It also takes advantage of the fact that Swift's string is productName
automatically up to UnsafePointer<UInt8>
as explained in String value for UnsafePointer <UInt8> behavior of function parameters . As mentioned in the comments on this thread, this is done by creating a temporary array UInt8
(or sequence?). This way you can explicitly specify the UTF-8 bytes and put them in 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.
}
Another possible solution (with an intermediate object NSData
):
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))
}
}
source to share