Undefined symbols for x86_64 architecture in Objective-C

Question

I am trying to implement a sample AVFoundation code found here in an Xcode project: http://developer.apple.com/library/mac/#qa/qa1740/_index.html#//apple_ref/doc/uid/DTS40011007

The only changes I made were to remove the links to autorelease, release and save, because I have automatic reference counting for the project. After successfully resolving these build errors, I now get Undefined characters for the x86_64 architecture. "

I run on Mountain Lion 10.8 and get no errors when importing AVFoundation.h into my header file, but it seems that AV * characters were not found?

The following is the error log, .h and .m. Could someone more knowledgeable help me determine where the problem (s) are?

Log:

Undefined symbols for architecture x86_64: "_AVCaptureSessionPresetMedium", referenced from: -[Recorder screenRecording:] in screenAppDelegate.o "_OBJC_CLASS_$_AVCaptureMovieFileOutput", referenced from: objc-class-ref in screenAppDelegate.o "_OBJC_CLASS_$_AVCaptureScreenInput", referenced from: objc-class-ref in screenAppDelegate.o "_OBJC_CLASS_$_AVCaptureSession", referenced from: objc-class-ref in screenAppDelegate.o ld: symbol(s) not found for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation) 

.h

 #import <Cocoa/Cocoa.h> #import <Foundation/Foundation.h> #import <AVFoundation/AVFoundation.h> @interface screenAppDelegate : NSObject <NSApplicationDelegate> @end @interface Recorder : NSObject <AVCaptureFileOutputRecordingDelegate> { @private AVCaptureSession *mSession; AVCaptureMovieFileOutput *mMovieFileOutput; NSTimer *mTimer; } -(void)screenRecording:(NSURL *)destPath; @end 

.m

 #import "screenAppDelegate.h" @implementation screenAppDelegate - (void)applicationDidFinishLaunching:(NSNotification *)aNotification { // Insert code here to initialize your application } @end @implementation Recorder -(void)screenRecording:(NSURL *)destPath { // Create a capture session mSession = [[AVCaptureSession alloc] init]; // Set the session preset as you wish mSession.sessionPreset = AVCaptureSessionPresetMedium; // If you're on a multi-display system and you want to capture a secondary display, // you can call CGGetActiveDisplayList() to get the list of all active displays. // For this example, we just specify the main display. CGDirectDisplayID displayId = kCGDirectMainDisplay; // Create a ScreenInput with the display and add it to the session AVCaptureScreenInput *input = [[AVCaptureScreenInput alloc] initWithDisplayID:displayId]; if (!input) { //[mSession release]; mSession = nil; return; } if ([mSession canAddInput:input]) [mSession addInput:input]; // Create a MovieFileOutput and add it to the session mMovieFileOutput = [[AVCaptureMovieFileOutput alloc] init]; if ([mSession canAddOutput:mMovieFileOutput]) [mSession addOutput:mMovieFileOutput]; // Start running the session [mSession startRunning]; // Delete any existing movie file first if ([[NSFileManager defaultManager] fileExistsAtPath:[destPath path]]) { NSError *err; if (![[NSFileManager defaultManager] removeItemAtPath:[destPath path] error:&err]) { NSLog(@"Error deleting existing movie %@",[err localizedDescription]); } } // Start recording to the destination movie file // The destination path is assumed to end with ".mov", for example, @"/users/master/desktop/capture.mov" // Set the recording delegate to self [mMovieFileOutput startRecordingToOutputFileURL:destPath recordingDelegate:self]; // Fire a timer in 5 seconds mTimer = [NSTimer scheduledTimerWithTimeInterval:5 target:self selector:@selector(finishRecord:) userInfo:nil repeats:NO]; } -(void)finishRecord:(NSTimer *)timer { // Stop recording to the destination movie file [mMovieFileOutput stopRecording]; //[mTimer release]; mTimer = nil; } // AVCaptureFileOutputRecordingDelegate methods - (void)captureOutput:(AVCaptureFileOutput *)captureOutput didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL fromConnections:(NSArray *)connections error:(NSError *)error { NSLog(@"Did finish recording to %@ due to error %@", [outputFileURL description], [error description]); // Stop running the session [mSession stopRunning]; // Release the session //[mSession release]; mSession = nil; } 

Answer 1

Importing header files is not enough; you also need to add the AVFoundation structure to your project. This error comes from the linker, not from the compiler itself - you can find the AVFoundation headers, and compiling your source files was successful, but the linker could not make the executable from the resulting object files, as you did not say (via Xcode settings) it communicates with the infrastructure AVFoundation.

See this article on the compilation process to see why this happens.