NSSetUncaughtExceptionHandler doesn't work on mac - macos

Question

My code is here:
in myAppDelegate.m:
void catchException(NSException *e)
{
NSLog( #"here is a exception");
}
#implementation myAppDelegate
{
NSSetUncaughtExceptionHandler(&catchException);
NSException *e = [[NSException alloc] initWithName: #"aException" reason: #"test" userInfo: nil];
#throw e;
}
However the function catchException is never be trapped. Can anybody tell me why?

Answer 1

I have found in my own OSX code that I had to use NSExceptionHandler in order to reliably catch exceptions:
#import <Cocoa/Cocoa.h>
#import <ExceptionHandling/NSExceptionHandler.h>
#import "CocoaUtil.h"
#import <execinfo.h>
// ExceptionDelegate
#interface ExceptionDelegate : NSObject
#end
static ExceptionDelegate * _exceptionDelegate = nil;
int main(int argc, const char **argv) {
int retval = 1;
#autoreleasepool
{
//
// Set exception handler delegate
//
_exceptionDelegate = [[ExceptionDelegate alloc] init];
NSExceptionHandler *exceptionHandler = [NSExceptionHandler defaultExceptionHandler];
exceptionHandler.exceptionHandlingMask = NSLogAndHandleEveryExceptionMask;
exceptionHandler.delegate = _exceptionDelegate;
//
// Set signal handling
//
int signals[] = {
SIGQUIT, SIGILL, SIGTRAP, SIGABRT, SIGEMT, SIGFPE, SIGBUS, SIGSEGV,
SIGSYS, SIGPIPE, SIGALRM, SIGXCPU, SIGXFSZ
};
const unsigned numSignals = sizeof(signals) / sizeof(signals[0]);
struct sigaction sa;
sa.sa_sigaction = signalHandler;
sa.sa_flags = SA_SIGINFO;
sigemptyset(&sa.sa_mask);
for (unsigned i = 0; i < numSignals; i++)
sigaction(signals[i], &sa, NULL);
// Do work
} // #autoreleasepool
return retval;
}
static void dumpStack(void **frames, unsigned numFrames) {
char **frameStrings = backtrace_symbols(frames, numFrames);
if (frameStrings) {
for (unsigned i = 0; i < numFrames && frameStrings[i] ; i++)
logbareutf8((char *)frameStrings[i]);
free(frameStrings);
} else {
logerr(#"No frames to dump");
}
}
static void signalHandler(int sig, siginfo_t *info, void *context) {
logerr(#"Caught signal %d", sig);
const size_t maxFrames = 128;
void *frames[maxFrames];
unsigned numFrames = backtrace(frames, maxFrames);
dumpStack(frames, numFrames);
bool send = criticalAlertPanel(#"Application Error",
#"Upload logfile to support site",
#"MyApp is terminating due to signal %d", sig);
if (send)
sendLogfile();
exit(102);
}
static void sendLogfile() {
// Redacted
}
#implementation ExceptionDelegate
- (BOOL)exceptionHandler:(NSExceptionHandler *)exceptionHandler
shouldLogException:(NSException *)exception
mask:(NSUInteger)mask {
logerr(#"An unhandled %# exception occurred: %#", [exception name], [exception reason]);
// [exception callStackReturnAddresses] will be empty, so parse the NSStackTraceKey from
// [exception userInfo].
NSString *stackTrace = [[exception userInfo] objectForKey:NSStackTraceKey];
NSScanner *scanner = [NSScanner scannerWithString:stackTrace];
NSMutableArray *addresses = [[NSMutableArray alloc] initWithCapacity:0];
NSCharacterSet *whitespace = [NSCharacterSet whitespaceAndNewlineCharacterSet];
NSString *token;
while ([scanner scanUpToCharactersFromSet:whitespace
intoString:&token]) {
[addresses addObject:token];
}
NSUInteger numFrames = [addresses count];
if (numFrames > 0) {
void **frames = (void **)malloc(sizeof(void *) * numFrames);
NSUInteger i, parsedFrames;
for (i = 0, parsedFrames = 0; i < numFrames; i++) {
NSString *address = [addresses objectAtIndex:i];
if (![CocoaUtil parseString:address toVoidPointer:&frames[parsedFrames]]) {
logerr(#"Failed to parse frame address '%#'", address);
break;
}
parsedFrames++;
}
if (parsedFrames > 0) {
logerr(#"Stack trace:");
dumpStack(frames, (unsigned)parsedFrames);
}
free(frames);
} else {
logerr(#"No addresses in stacktrace");
}
return YES;
}
- (BOOL)exceptionHandler:(NSExceptionHandler *)exceptionHandler
shouldHandleException:(NSException *)exception
mask:(NSUInteger)mask {
bool send = criticalAlertPanel(#"Application Error",
#"Upload logfile to support site",
#"MyApp is terminating due to an unhandled exception:\n\n%#",
[exception reason]);
if (send)
sendLogfile();
exit(101);
// not reached
return NO;
}

Answer 2

You'll need to import ExceptionHandling.framework as noted by trojanfoe.
Here is gist which cleans up the stack trace printing (some functions are missing):
https://gist.github.com/alfwatt/5ddfaf68e530a5a69e3d