C++ vector as member of Objective C class doesn't retain value - objective-c++

Question

So I've got an Objective C class that will implement the NSTableViewDataSource protocol to display a list of audio output devices. I'm calling a C++ class that returns device information as a std::vector of C structs of the form
typedef struct DeviceInfo {
AudioDeviceID devID;
char name[128];
int nInputChannels;
int nOutputChannels;
} DeviceInfo;
The Objective C class is
#interface PreferencesViewController : NSObject <NSTableViewDataSource> {
AudioOutputController *audioOutputController_;
vector<DeviceInfo> audioOutputDevices_;
}
- (void)setAudioOutputController:(AudioOutputController *)controller;
- (void)updateDeviceList;
- (IBAction)buttonPressed:(id)sender;
#end
The main app controller sets the PreferencesViewController's AudioOutputController member (the C++ class), then calls updateDeviceList(), which tells the AudioOutputController to query the available audio devices and return a vector of DeviceInfo structs
- (void)updateDeviceList {
/* Update the list of currently connected devices and return device information */
audioOutputController_->setAvailableDevices();
audioOutputDevices_.clear();
audioOutputDevices_ = audioOutputController_->getAvailableDevices();
for (int i = 0; i < audioOutputDevices_.size(); i++) {
printf("Device %d: %s\n", i, audioOutputDevices_[i].name);
printf("\t%d Output Channels\n", audioOutputDevices_[i].nOutputChannels);
}
}
This all works completely fine and prints the available audio devices, but the vector of structs doesn't seem to retain its value outside updateDeviceList(), so I see an empty vector when I try to access it in the NSTableViewDataSource protocol methods. If I try to just print the size of the vector in an IBAction method, for example
- (IBAction)buttonPressed:(id)sender {
printf("audioOutputDevices_.size() = %lu\n", audioOutputDevices_.size());
}
it says the vector is empty. I'm new to combining C++ and Objective C, so any help is greatly appreciated.
Edit: something else peculiar. If I call PreferencesViewController's updateDeviceList() method from the AppDelegate's applicationDidFinishLaunching(), as follows:
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
audioOutputController_ = new AudioOutputController();
preferences_ = [[PreferencesViewController alloc] init];
[preferences_ setAudioOutputController:audioOutputController_];
[preferences_ updateDeviceList:self];
}
#end
then I get the problem stated above, with the C++ vector not retaining its value. If I instead make updateDeviceList() an IBAction callback for an interface button, then when I call it it retains its value and the device information gets added to the table.

Answer 1

I believe (from a similar experience of mine) that during application startup the C++ constructor of vector<DeviceInfo> audioOutputDevices_ is somehow called again, which clears it.