Question

I’m using a 3rd party class that contain the following extention:

@interface BaseClass ()
{
   int privateMember;
}
@end

i’ve created my own subclass:

  @interface SubClass : BaseClass {
  }
  @end

is there a way to access privateMember in SubClass?

---

EDIT:
actual code

GPUImageMovie.m: (base class)

@interface GPUImageMovie ()
{
    BOOL audioEncodingIsFinished, videoEncodingIsFinished;
    GPUImageMovieWriter *synchronizedMovieWriter;
    CVOpenGLESTextureCacheRef coreVideoTextureCache;
    AVAssetReader *reader;
}

MultiTrackGPUImageMovie.h (subclass)

@interface MultiTrackGPUImageMovie : GPUImageMovie {
}
...
@end

MultiTrackGPUImageMovie.m (subclass)

 - (void)processMovieFrame:(CMSampleBufferRef)movieSampleBuffer forTarget:(int)targetToSendIdx {
 ...
 CVReturn err = CVOpenGLESTextureCacheCreateTextureFromImage(kCFAllocatorDefault,       coreVideoTextureCache, movieFrame, NULL, GL_TEXTURE_2D, GL_RGBA, bufferWidth, bufferHeight,   GL_BGRA, GL_UNSIGNED_BYTE, 0, &texture);
 ...
}

give error
Use of undeclared identifier ‘coreVideoTextureCache’

Answer 1

It depends on how the ‘private’ member has been declared. If there wasn’t the @private keyword before it, i. e. it was really

@interface BaseClass ()
{
    int privateMember;
}
@end

and not

@interface BaseClass ()
{
    @private
    int privateMember;
}
@end

then you can easily reference this instance variable simply by using its name – the default access scope for instance variables is protected, i. e. not accessible outside the class, but accessible from subclasses.

However, if it was declared as private, you’ll have to fall back using the runtime functions; in your subclass, declare and implement this method:

- (void *)pointerForIvarWithName:(NSString *)name
{
    Ivar ivar = class_getInstanceVariable([self class], [name UTF8String]);
    return ((char *)self) + ivar_getOffset(ivar);
}

Then use it like this:

int ivarPtr;
ivarPtr = *(int *)[self pointerForIvarWithName:@"privateMember"];

Edit: so it seems the member you’re trying to access is in a class extension and not public in the header file. In this case, you can go for the 2nd solution only (although it’s not advised to do so).