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.

I think if you had `const char*` argument on C side it would work seamlessly. — Wojtek Surowka, Aug 19 '14 at 08:40
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! — Mads Gadeberg, Aug 19 '14 at 08:47
@WojtekSurowka: I think you should rewrite your comment as an answer so that it can be marked as the solution — Antonio, Aug 19 '14 at 08:51

Wojtek Surowka · Accepted Answer · 2014-08-19T09:00:14.187

6

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";

edited Aug 19 '14 at 09:00

answered Aug 19 '14 at 08:52

Wojtek Surowka

8

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` and Swift strings can automatically bridge to that. The type `CString` has been removed from the language. – Mecki Sep 06 '16 at 21:15

score 2 · Answer 2 · answered Jan 23 '20 at 07:08

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*

2 Answers2