Objective-C 中架构 x86_64 的未定义符号

Posted 2023-03-07

【中文标题】Objective-C 中架构 x86_64 的未定义符号

【英文标题】：Undefined symbols for architecture x86_64 in Objective-C

【发布时间】：2012-08-16 22:16:25

【问题描述】：

我正在尝试实现在 Xcode 项目中找到的 AVFoundation 示例代码：http://developer.apple.com/library/mac/#qa/qa1740/_index.html#//apple_ref/doc/uid/DTS40011007

我所做的唯一修改是删除对自动释放、释放和保留的引用，因为我为项目启用了自动引用计数。成功解决了这些构建错误后，我现在得到“架构 x86_64 的未定义符号”。

我在 Mountain Lion 10.8 上运行，将 AVFoundation.h 导入头文件时没有出现错误，但似乎找不到 AV* 符号？

以下是错误日志、.h 和 .m 代码。有没有更博学的人可以帮我找出问题所在？

日志：

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;

【参考方案1】：

仅仅导入头文件是不够的，你还得把 AVFoundation 框架添加到你的项目中。此错误来自链接器，而不是编译器本身 - 可以找到 AVFoundation 标头并且源文件的编译成功，但是链接器无法从生成的目标文件中生成可执行文件，因为您没有告诉它（通过 Xcode 的设置）链接到 AVFoundation 框架。

请参阅this article on the compilation process 了解为什么会发生这种情况。