Linker error declaring a function inside class

Question

I thought to know how to declare functions inside .m files, but here I get a linker error.I declare this in the .h file:

#import <Foundation/Foundation.h>
// Other rimports

void SQLite3HelperHandle(NSError* error);

@interface SQLite3Helper : NSObject

// Method signatures

@end

Then in the .m file:

#import "SQLite3Helper.h"

void SQLite3HelperHandle(NSError* error)
{
    // Method body
}

@implementation SQLite3Helper

// Methods implementation

@end

But I get a linker error.And the error has a lot of unreadable information.The only relevant thing is:

"_SQLite3HelperHandleError", referenced from:

Also, how do I declare it inline? I tried declaring it this way in the header:

extern inline void SQLite3HelperHandle(NSError* error);

And normally in the .m file:

void SQLite3HelperHandle(NSError* error);

I also tried other ways to do it, but never found the way to silent that linker error.
It should be as fast as a macro, but the function it too long to write and I prefer type checking so that's why I need an inline function.

score 2 · Answer 1 · edited May 23 '17 at 12:21

2

Looks like C++ style function name mangling.

To solve it, put your C-style function declaration (in your .h file) between this conditional:

#ifdef __cplusplus
extern "C" {
#endif

void SQLite3HelperHandle(NSError* error);

#ifdef __cplusplus
}
#endif

More information about what this is doing can be seen in this related question or this one.

edited May 23 '17 at 12:21

Community

1
1

answered Dec 15 '12 at 21:44

Michael Dautermann

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Thanks, that was very helpful in my case! – Julian D. Jul 01 '13 at 09:55

score 1 · Accepted Answer · answered Dec 15 '12 at 21:44

1

It sounds like the .m file needs to be included in the target you're building.

I use FOUNDATION_EXPORT void ... in the .h and just what you have in the .m file.

answered Dec 15 '12 at 21:44

paulmelnikow

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Did you make sure the .m file is included in the target you're building? The linker error likely has to do with the .m file, not the .h file. – paulmelnikow Dec 15 '12 at 22:00
Is that under compile sources? Under compile sources I see that .m file, or do I have to check to another place? – Ramy Al Zuhouri Dec 15 '12 at 23:32
However the class gets compiled because I can use all of it's methods. – Ramy Al Zuhouri Dec 15 '12 at 23:42
Yes, looks like you got it. – paulmelnikow Dec 16 '12 at 03:22
What did you do that actually fixed your problem? – paulmelnikow Dec 16 '12 at 17:41

score 0 · Answer 3 · answered Dec 15 '12 at 23:09

0

To make a function inline define it as static inline, whether it's in a header or not. If you only need it in one file, just define it in that .m file and leave it out of the header. Otherwise, define it entirely in the .h file.

answered Dec 15 '12 at 23:09

Wade Tregaskis

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Linker error declaring a function inside class

3 Answers3