Calling a C function from within a function in a .mm file

Question

This is one of those problems that is a bit vague and so difficult to pinpoint the cause. I'll try to keep it simple.

I've created a C class with a header like this:

C_Class.h

void do_something(void);

C_Class.c

void do_something(void)
{
}

Then I have a .mm file that was working perfectly fine until within one of its functions I added my C sub_routine which I created earlier:

  #import "C_Class.h" // included in the .h file 


 // then in the .mm file

 - (void)working_function{
  .... some working code ......
  do_something();

  }

The problem is I get this error:

 -[MyDotMMfile working_function] in MyDotMMfile.o
 Symbol(s) not found
 Collect2:ld returned 1 exit status

This questioned has been answered elsewhere, but the response doesn't seem relevant to my situation. I'm working in XCode and have stopped running my app, rebuilt it and still get the same error. Since I'm new to programming I have a feeling it has to do with how I'm calling my C functions.

Any help?

EDIT 1

If anyone is feeling so altruistic they may download the actually files here.

Show the working_function declaration please. It should be the Objective-C class function by the way — Andrew, Feb 13 '11 at 14:03
I'm in middle of posting the entire code. Please give me a moment :) — Eric Brotto, Feb 13 '11 at 14:12
try to call something from math.h to determine if your problem rely upon c or objective-c. And also is it a compiler or linker error ? — Andrew, Feb 13 '11 at 14:23
The Build fails, but I believe this type of error is inherently a linker error, no? — Eric Brotto, Feb 13 '11 at 14:40
I've called a math function and there doesn't seem to be a problem. Any ideas? — Eric Brotto, Feb 13 '11 at 14:43

score 7 · Answer 1 · answered Feb 13 '11 at 19:13

The .mm file is looking to call a mangled version of the function name. You need either __BEGIN_DECLS and __END_DECLS around the C function declarations seen by the C++-compiled file, or you need to do the equivalent yourself. The idea is to mark those function declarations as extern "C" when seen by an (Obj-)C++ compiler, but not when seen by any other sort of compiler.

score 0 · Accepted Answer · edited May 23 '17 at 12:18

0

Somehow I managed to figure out the problem. It had to do with a missing file. The solution I used I found here.

edited May 23 '17 at 12:18

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answered Feb 13 '11 at 16:00

Eric Brotto

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Calling a C function from within a function in a .mm file

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