Implementing a header in Objective C - objective-c

Question

I'm completely new to Objective C and I'm trying to use it to wrap a C-library. I have a main.m wrap.m and wrap.h files. From what I gather in the header file I included #interface and in the source file I will include #implementation However I'm not really understanding what to include in each of them. Right now my main file is:
int copy_data(struct archive *ar, struct archive *aw) {
for (;;) {
const void *buff;
size_t size;
off_t offset;
int r = archive_read_data_block(ar, &buff, &size, &offset);
if (r == ARCHIVE_EOF)
return (ARCHIVE_OK);
archive_write_data_block(aw, buff, size, offset);
}
}
int main(int argc, const char * argv[])
{
#autoreleasepool {
struct archive *a;
struct archive *ext;
struct archive_entry *entry;
int flags;
int r;
/* Select which attributes we want to restore. */
flags = ARCHIVE_EXTRACT_TIME;
flags |= ARCHIVE_EXTRACT_PERM;
flags |= ARCHIVE_EXTRACT_ACL;
flags |= ARCHIVE_EXTRACT_FFLAGS;
a = archive_read_new();
archive_read_support_format_all(a);
archive_read_support_compression_all(a);
ext = archive_write_disk_new();
archive_write_disk_set_options(ext, flags);
archive_write_disk_set_standard_lookup(ext);
r = archive_read_open_filename(a, argv[1], 10240);
for (;;) {
r = archive_read_next_header(a, &entry);
if (r == ARCHIVE_EOF)
break;
r = archive_write_header(ext, entry);
if (archive_entry_size(entry) > 0) {
copy_data(a, ext);
}
archive_write_finish_entry(ext);
}
archive_read_close(a);
archive_read_free(a);
archive_write_close(ext);
archive_write_free(ext);
NSLog(#"No Issues");
}
return 0;
}
So far what I'm getting in my wrap.h file is:
typedef struct{
int *a;
int *ext;
}archive;
#interface main : NSObject
#property int flags;
#property int r;
I don't know if that is close to what I need to do, and I'm getting errors on my ARCHIVE_EXTRACT saying they are undeclared identifiers which I assume also have to go into my wrap.h file but I'm not sure how to do that. Any help at all would be appreciated!

Answer 1

If you start your project in Xcode using the CommandLineTool template, you can select your language to be "C" or "C++", so you wouldn't have to mess with Objective-C at all.
As for the .h file that you currently have, don't do "#property" or "#interface" for "main". "main" is a C style function and not an Objective-C thing.

Answer 2

If you are actually interested in an objectivec solution, follow Michael Dautermann's instructions to start a new Command Line project but instead of Type C use the Foundation option. This will give you a working main (just a regular c function). Then select new->objective c class to create your wrap.h/wrap.m. In the wrap.h you will pretty much exclusively be declaring your own objectivec public wrapper methods. In the wrap.m, you'll be importing what you want to wrap, and defining your wrapper functions.
//
// main.m
//
#import <Foundation/Foundation.h>
#import "wrap.h"
int main(int argc, const char * argv[])
{
#autoreleasepool {
[wrap wrappedStuff];
}
return 0;
}
//
// wrap.h
//
----------
#import <Foundation/Foundation.h>
#interface wrap : NSObject
+ (void)wrappedStuff;
#end
//
// wrap.m
//
#import "wrap.h"
#include "WhatImWrapping.h"
#implementation wrap
int copy_data(struct archive *ar, struct archive *aw) {
for (;;) {
const void *buff;
size_t size;
off_t offset;
int r = archive_read_data_block(ar, &buff, &size, &offset);
if (r == ARCHIVE_EOF)
return (ARCHIVE_OK);
archive_write_data_block(aw, buff, size, offset);
}
}
+ (void)wrappedStuff
{
struct archive *a;
struct archive *ext;
struct archive_entry *entry;
int flags;
int r;
/* Select which attributes we want to restore. */
flags = ARCHIVE_EXTRACT_TIME;
flags |= ARCHIVE_EXTRACT_PERM;
flags |= ARCHIVE_EXTRACT_ACL;
flags |= ARCHIVE_EXTRACT_FFLAGS;
a = archive_read_new();
archive_read_support_format_all(a);
archive_read_support_compression_all(a);
ext = archive_write_disk_new();
archive_write_disk_set_options(ext, flags);
archive_write_disk_set_standard_lookup(ext);
r = archive_read_open_filename(a, argv[1], 10240);
for (;;) {
r = archive_read_next_header(a, &entry);
if (r == ARCHIVE_EOF)
break;
r = archive_write_header(ext, entry);
if (archive_entry_size(entry) > 0) {
copy_data(a, ext);
}
archive_write_finish_entry(ext);
}
archive_read_close(a);
archive_read_free(a);
archive_write_close(ext);
archive_write_free(ext);
NSLog(#"No Issues");
}
#end