How to use pure C files in an objective-c project?

Question

Simple question:

I have created a bunch of C helper routines and am trying to include them in a project. I had assumed something like the following would be ok.

MyFuncs.h

typedef struct
{
    float n;
} MyStruct;

float Operation(MyStruct ms);

MyFuncs.m

#import "MyFuncs.h"

float Operation(MyStruct ms)
{
    return ms.n * ms.n;
}

However, I'm getting a linker error "Undefined symbols for architecture i386" and "Operation(MyStruct) referenced from x"

Is there some other way that header/implemenation C files need to be set-up to work?

Note: This is for an iOS project using Xcode 4.5.

SOrry, I should have said this is for an iOS project using the XCode 4.5 IDE — Tricky, Oct 18 '12 at 17:44
I've taken the liberty of editing your comment into the question -- you're free to edit your own questions if you realize you left something out. — Dietrich Epp, Oct 18 '12 at 17:58

Dietrich Epp · Accepted Answer · 2012-10-18T17:58:40.793

3

No, there is no problem with using pure C. Usually, the source files will be named *.c instead of *.m, but renaming *.c to *.m shouldn't cause errors.

However, there's a clue:

Operation(MyStruct) referenced from x

If the linker knows the type of the function parameters, it's because you're calling the function from C++ code. You will have to put extern "C" { ... } in the header as follows:

#ifdef __cplusplus
extern "C" {
#endif

typedef struct
{
    float n;
} MyStruct;

float Operation(MyStruct ms);

#ifdef __cplusplus
}
#endif

If you don't have any C++ in your project (including Objective-C++ *.mm files), then this isn't your problem.

edited Oct 18 '12 at 17:58

answered Oct 18 '12 at 17:49

Dietrich Epp

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Make sure also to put `extern "C"` inside an `#ifdef __cplusplus` – asveikau Oct 18 '12 at 17:56
@asveikau: Righto. I've been doing it all automatically for so long it's easy to forget... – Dietrich Epp Oct 18 '12 at 17:59
Great spot! Yes, i'm migrating a couple of C++ classes to C to simplify my project a little. – Tricky Oct 19 '12 at 09:54

score 0 · Answer 2 · answered Oct 18 '12 at 17:49

0

If it's pure c then "MyFuncs.c" instead of "MyFuncs.m" will be better.

answered Oct 18 '12 at 17:49

Mr Bonjour

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score -4 · Answer 3 · answered Oct 18 '12 at 17:47

-4

Call the implementation file with extension .mm like MyFuncs.mm.

answered Oct 18 '12 at 17:47

Daniel

577
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Objective-C++ (.mm) and C (.c) are very different languages. – Catfish_Man Oct 18 '12 at 18:12

How to use pure C files in an objective-c project?

3 Answers3

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