How to compile Objective C code in ubuntu

Question

I am beginner in Iphone programming. I am trying to compile (ubuntu).

#import <Foundation/Foundation.h>

int main (void)
 {
  NSLog (@"Executing");
  return 0;
 }

I compiled it but getting following error

   subhash@subhash-Lenovo-G570:~/grit/iphone/mac$ gcc -lgnustep-base -lpthread -lob
  jc -lm -I/usr/local/include/GNUstep -I/usr/include/GNUstep -fconstant-string-cla
  ss=NSConstantString hello.m -o hello
  In file included from /usr/include/GNUstep/Foundation/NSClassDescription.h:30:0,
                  from /usr/include/GNUstep/Foundation/Foundation.h:50, 
                  from hello.m:1:
  /usr/include/GNUstep/Foundation/NSException.h:42:2: error: #error The current se
  tting for native-objc-exceptions does not match that of gnustep-base ... please 
  correct this.

i followed the http://ubuntuforums.org/showthread.php?p=5593608 as a reference.

I commented #error directive of NSException.h and problem is solved. Now i am getting new error.

/tmp/ccQlI9wJ.o: In function `main':
        hello.m:(.text+0x11): undefined reference to `NSLog'
        /tmp/ccQlI9wJ.o: In function `__objc_gnu_init':
        hello.m:(.text+0x2a): undefined reference to `__objc_exec_class'
        /tmp/ccQlI9wJ.o:(.data+0x40): undefined reference to `__objc_class_name_NSConsta
        ntString'
        collect2: ld returned 1 exit status

I had to comment out that error in NSException.h, nothing else worked. — user529758
– user529758, Commented Jul 6, 2012 at 7:52
that's what I just wrote. Comment out the #error directive in the header file. — user529758
– user529758, Commented Jul 6, 2012 at 8:14
I think it's a much better idea to avoid all packages and install GNUstep directly from trunk. And use clang. Or use this one lists.gnu.org/archive/html/discuss-gnustep/2012-10/… — Fred Frith-MacDonald
– Fred Frith-MacDonald, Commented Feb 4, 2013 at 23:27

Community · Accepted Answer · 2020-06-20 09:12:55Z

in Compile Objective-C Programs Using gcc there is the following

Also note that if you did not include -D_NATIVE_OBJC_EXCEPTIONS, you may run into the following error:
/usr/include/GNUstep/Foundation/NSException.h:42:2: error: #error The
current setting for native-objc-exceptions does not match that of
gnustep-base ... please correct this.

I has the same error as the original poster did, and passing the -D_NATIVE_OBJC_EXCEPTIONS flag fixed the problem for me. I was trying to do something pretty non-standard, so it might not work for everyone.

Note that shalki's answer may also fix the issue. In case the link referenced there vanishes, the blog post in question, Compile Objective-C Programs on Linux is in Chinese or Japanese or something like that, so I don't know exactly what it is saying, but I think the upshot is to pass

`gnustep-config --objc-flags`

as an argument to gcc. The post has

gcc `gnustep-config --objc-flags` hello.m -o hello -I /usr/include/GNUstep/ -L /usr/lib/GNUstep/ -lgnustep-base

at the end. Now, on my machine, gnustep-config --objc-flags expands to

-MMD -MP -DGNUSTEP -DGNUSTEP_BASE_LIBRARY=1 -DGNU_GUI_LIBRARY=1 -DGNU_RUNTIME=1 -DGNUSTEP_BASE_LIBRARY=1 -D_REENTRANT -fPIC -Wall -DGSWARN -DGSDIAGNOSE -Wno-import -g -O2 -fno-strict-aliasing -fexceptions -fobjc-exceptions -D_NATIVE_OBJC_EXCEPTIONS -fgnu-runtime -fconstant-string-class=NSConstantString -I. -I/home/faheem/GNUstep/Library/Headers -I/usr/local/include/GNUstep -I/usr/include/GNUstep

Yowza. Notice that this list of flags does contain-D_NATIVE_OBJC_EXCEPTIONS, along with lots of other stuff. For the record, my machine is running Debian squeeze. This might be a Debian/Ubuntu specific problem. I'm not sure.

Yeah, this did the trick for me. I simply expanded gnustep-config --objc-flags and used all parameters except D_NATIVE_OBJC_EXCEPTIONS. Good catch!

Fred Frith-MacDonald · Accepted Answer · 2013-02-04 23:20:49Z

0

Better write a GNUmakefile.

http://www.gnustep.it/nicola/Tutorials/WritingMakefiles/index.html

And better stop using gcc and switch to clang.

answered Feb 4, 2013 at 23:20

Fred Frith-MacDonald

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