Re: got error when compile

[David Chisnall]

On 8 Jul 2009, at 10:42, Apache wrote:

> Hi, I'm java developer and start learning objective c using GNUstep

Hi!


> say.h
> --------
> #ifndef _Say_H_
> #define _Say_H_
>
> #include <Foundation/NSObject.h>

In general, you should use #import on Objective-C headers, not  
include, and not put these #ifndef protections on them.  Using #import  
instead of #include automatically prevents multiple-inclusion.

The GNUstep headers work with #include because the GCC people went  
briefly insane a few years ago that they were going to deprecate  
#import.  A lot of other Objective-C headers, however, will not work  
with #include.

> @interface Say: NSObject
> {
> }
> - (void) sayHello;
> - (void) sayHelloTo: (NSString *)name;
> @end

Don't forget that you also need an implementation of the class.  If  
you attempt to instantiate a class which doesn't exist then you will  
get errors.

> $ gcc -o main main.m
> In file included from main.m:1:
> say.h:4:33: Foundation/NSObject.h: No such file or directory
> In file included from main.m:1:
> say.h:7: error: cannot find interface declaration for `NSObject',
> superclass of
> `Say'

The problem here is, as it says, that it can't find the location of  
the headers.  If you want to compile like this then you will need to  
provide a -I command-line option providing the location of the GNUstep  
headers, and also add -lgnustep-base and an equivalent -L command  
specifying the location of the GNUstep library.

You are better off using GNUstep Make.  This is a set of GNU make  
files for building GNUstep things.  You probably want a GNUmakefile  
like this:

include $(GNUSTEP_MAKEFILES)/common.make

VERSION = 0.1
TOOL_NAME = example

$(TOOL_NAME)_OBJC_FILES = \
        say.m\
        test.m

include $(GNUSTEP_MAKEFILES)/tool.make

Just put that in a file called GNUmakefile and type 'make'.  Note that  
I'm assuming that you have a say.m file providing the implementation  
of the class described in say.h.  If you don't have one, then your  
code will compile but will fail to link.

David