How to pass a Swift string to a c function?

Question

I am having serious trouble passing a string from swift, to a function written in c.

I'm trying to do this in my swift code

var address = "192.168.1.2"
var port = 8888
initSocket(address, port)

The c function looks like this:

void initSocket(char *address, int port);

Im getting the error: Cannot convert the expression's of type 'Void' to type 'CMutablePointer'

I can't seem to find a solution that works.

• Wojtek Surowka: I think if you had const char* argument on C side it would work seamlessly.
• Mads Gadeberg: Wojtek you are my hero! Thank you so much.. Solution: Changed c function to initSocket(const char* address) and string declaration to `var address: CString = "192.168.1.2" Thanks again!
• David Ranieri: @WojtekSurowka, Looks like an answer to me.
• Antonio: @WojtekSurowka: I think you should rewrite your comment as an answer so that it can be marked as the solution

Answer 1

Swift CStrings work seamlessly with C constant strings, so use

void initSocket(const char *address, int port);

instead of char* argument, and declare your address variable as CString:

var address: CString = "192.168.1.2";

• Mecki: You may want to update that question. With Swift 2.2 or newer, Swift strings are not automatically bridged to C strings. C strings are now UnsafePointer<UInt8> and Swift strings can automatically bridge to that. The type CString has been removed from the language.

Answer 2

in C, declare your parameter like this

void setLastName(const char* lastName){
}

then in swift, you can directly pass in a regular swift string

setLastName("Montego");

the key is to define the variable with the asterisk immediately after the char in C like: const char*

source: https://developer.apple.com/swift/blog/?id=6