Compiling Objective-C project on Linux (Ubuntu)

Question

How to make an Objective-C project work on Ubuntu?

My files are:

Fraction.h

    #import <Foundation/NSObject.h>

    @interface Fraction: NSObject {
        int numerator;
        int denominator;
    }

    -(void) print;
    -(void) setNumerator: (int) n;
    -(void) setDenominator: (int) d;
    -(int) numerator;
    -(int) denominator;
    @end

Fraction.m

    #import "Fraction.h"
    #import <stdio.h>

    @implementation Fraction
    -(void) print {
        printf( "%i/%i", numerator, denominator );
    }

    -(void) setNumerator: (int) n {
        numerator = n;
    }

    -(void) setDenominator: (int) d {
        denominator = d;
    }

    -(int) denominator {
        return denominator;
    }

    -(int) numerator {
        return numerator;
    }
    @end

main.m

    #import <stdio.h>
    #import "Fraction.h"

    int main( int argc, const char *argv[] ) {
        // create a new instance
        Fraction *frac = [[Fraction alloc] init];

        // set the values
        [frac setNumerator: 1];
        [frac setDenominator: 3];

        // print it
        printf( "The fraction is: " );
        [frac print];
        printf( "\n" );

        // free memory
        [frac release];

        return 0;
    }

I've tried two approaches to compile it:

1. Pure gcc:

   $ sudo apt-get install gobjc gnustep gnustep-devel
   $ gcc `gnustep-config --objc-flags` -o main main.m -lobjc -lgnustep-base
   /tmp/ccIQKhfH.o:(.data.rel+0x0): undefined reference to `__objc_class_name_Fraction'
   

2. I created a GNUmakefile Makefile:

   include ${GNUSTEP_MAKEFILES}/common.make
   
   TOOL_NAME = main
   main_OBJC_FILES = main.m
   
   include ${GNUSTEP_MAKEFILES}/tool.make
   

   ... and ran:

   $ source /usr/share/GNUstep/Makefiles/GNUstep.sh
   $ make
   Making all for tool main...
    Linking tool main ...
   ./obj/main.o:(.data.rel+0x0): undefined reference to `__objc_class_name_Fraction'
   

So in both cases compiler gets stuck at

    undefined reference to `__objc_class_name_Fraction'

Do you have and idea how to resolve this issue?

Answer 1

It's right. In both cases you did not include Fraction.m in your list of files to be compiled, so it can't find the implementation of the class Fraction

From the comment, this command works

gcc `gnustep-config --objc-flags` -o main *.m -lobjc -lgnustep-base

Answer 2

I am not an expert at writing the make files like that, I find simply typing the following works on ubuntu quite well:

gcc -I /usr/include/GNUstep/ -I /usr/include/mysql -L /usr/lib/GNUstep/\
    -lgnustep-base -lmysqlclient\
    -g -ggdb\
    -fconstant-string-class=NSConstantString -o test *.m

I am using it on this project:

http://github.com/uptecs/SmsgateDelivery/

If the above GCC command does not work you have not installed enough packages, use apt-cache to search for more gcc and objective c packages to install (I just installed more packages that looked relevant at random until it worked)