Question

I have created a new class of type NSObject, which created two files — a .h and a .m file. Here is the code from the two files:

SocketConnection.h

#import <Foundation/Foundation.h>

@interface SocketConnection : NSObject
{

}

+ (SocketConnection *)getInstance;

@end

SocketConnection.m

#import "SocketConnection.h"
#import "imports.h"

static SocketConnection *sharedInstance = nil;

@implementation SocketConnection

- (id)init
{
    self = [super init];

    if (self) 
    {
        while(1)
        {
            Socket *socket;
            int port = 11005;
            NSString *host = @"199.5.83.63";

            socket = [Socket socket];

            @try
            {
                NSMutableData *data;
                [socket connectToHostName:host port:port];
                [socket readData:data];
                //  [socket writeString:@"Hello World!"];

                // Connection was successful //
                [socket retain]; // Must retain if want to use out of this action block.
            }
            @catch (NSException* exception) 
            {
                NSString *errMsg = [NSString stringWithFormat:@"%@",[exception reason]];
                NSLog(errMsg);
                socket = nil;
            }
        }
    }
    return self;
}

+ (SocketConnection *)getInstance
{
    @synchronized(self) 
    {
        if (sharedInstance == nil) 
        {
            sharedInstance = [[SocketConnection alloc] init];
        }
    }
    return sharedInstance;
}

@end 

And I seem to be getting a Linker error. When I comment out all the code in the SocketConnection.h/SocketConnection.m, the errors go away. I have several views in my project. I have a header file called “imports.h”, which I have imported SocketConnection.h, and included “imports.h” in my SocketConnection.m file. Any help would be greatly appreciated, since I seem to be stuck here :/. Thanks!

Errors:

Undefined symbols for architecture i386:
"_OBJC_CLASS_$_Socket", referenced from:
objc-class-ref in SocketConnection.o
(maybe you meant: _OBJC_CLASS_$_SocketConnection)
ld: symbol(s) not found for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Answer 1

You need to #import “Socket.h” at the top of you .m file.

The error here

    "_OBJC_CLASS_$_Socket", referenced from:
objc-class-ref in SocketConnection.o

is saying that SocketConnection is referencing an Objective-C class named “Socket” that it does not know about.