Call variadic Objective-C function from Swift

Question

I have summarized the steps of the problem, I have a C function defined in Objective-C:

ObjC.h

#import <Foundation/Foundation.h>

void cuslog(NSString *format, ...);

@interface ObjC : NSObject

@end

ObjC.m

#import "ObjC.h"

@implementation ObjC

@end

void cuslog(NSString *format, ...)
{
     // Implementation
}

I exposed it in Bridging-Header.h:

#import "ObjC.h"

// Also tried to put this line in bridging header
void cuslog(NSString *format, ...);

In Swift I intend to call the function like this:

cuslog("Some log")

But the error says:

"Use of unresolved identifier 'cuslog'"

What is the correct way to call the function in Swift?

Possible duplicate of How do you call an Objective-C variadic method from Swift? — jscs
– jscs, Commented Jul 26, 2017 at 21:26

user1720115 · Accepted Answer · 2014-06-23 20:25:23Z

5

According to the Swift devs, C variadic functions are not compatible with Swift variadics, so you won't be able to call your function directly.

The only workaround at this time is to write a non-variadic wrapper in C or Obj-C, and call that from Swift.

answered Jun 23, 2014 at 20:25

user1720115

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1 Comment

newacct Over a year ago

Plus, any decent API with C/Obj-C variadic functions should have a non-variadic version that takes a va_list argument, or a way to add elements one by one. Either of these are callable from Swift.

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