Backtrace category on NSObject

NSObject+Backtrace.h

@interface NSObject (Backtrace)

+ (NSString *)appBacktraceOfDepth:(int)depth fromStackSymbols:(NSArray *)frames;
+ (NSString *)backtraceOfDepth:(int)depth fromStackSymbols:(NSArray *)frames;
+ (NSString *)backtraceOfDepth:(int)depth fromStackSymbols:(NSArray *)frames matching:(NSString *)from;

@end

#define BACKTRACE_DEPTH(DEPTH) ([[NSThread class] respondsToSelector:@selector(callStackSymbols)] ? [NSObject appBacktraceOfDepth:DEPTH fromStackSymbols:[NSThread callStackSymbols]] : @"")
#define CALLSTACK_DEPTH(DEPTH) BACKTRACE_DEPTH(DEPTH)

NSObject+Backtrace.m

@implementation NSObject (Backtrace)

+ (NSString *)appBacktraceOfDepth:(int)depth fromStackSymbols:(NSArray *)frames {
	return [self backtraceOfDepth:depth fromStackSymbols:frames matching:[[NSBundle mainBundle] objectForInfoDictionaryKey:(NSString *)kCFBundleNameKey]];
}

+ (NSString *)backtraceOfDepth:(int)depth fromStackSymbols:(NSArray *)frames {
	return [self backtraceOfDepth:depth fromStackSymbols:frames matching:nil];
}

+ (NSString *)backtraceOfDepth:(int)depth fromStackSymbols:(NSArray *)frames matching:(NSString *)from {
	NSRegularExpression *regex = nil;
	if (!NSClassFromString(@"NSRegularExpression") || !(regex = [NSRegularExpression regularExpressionWithPattern:@"[0-9]+ +(.+[^ ]) +0x[0-9a-f]+ (.+) \\+ [0-9a-f]+" options:0 error:nil]))
		return [[frames objectAtIndex:1] substringFromIndex:51]; // no regex, be lame and rely on column counts
	NSString *result = nil;
	for (int goodframes=0, framenum=1; goodframes < depth && framenum < [frames count]; ++framenum) {
		NSString *frame = [frames objectAtIndex:framenum];
		NSTextCheckingResult *match = [regex firstMatchInString:frame options:0 range:NSMakeRange(0, [frame length])];
		if (!match) NSAssert1(NO, @"unparsed stack frame: %@", frame);
		if (from && ![from isEqualToString:[regex replacementStringForResult:match inString:frame offset:0 template:@"$1"]]) continue;
		++goodframes;
		NSString *caller = [regex replacementStringForResult:match inString:frame offset:0 template:@"$2"];
		if (from && goodframes == 1 && [caller isEqualToString:@"main"]) return [self backtraceOfDepth:depth fromStackSymbols:frames matching:nil]; // no useful calls from us, take ones from anyone instead
		result = !result ? caller : [result stringByAppendingFormat:@" < %@", caller];
	}
	return result ? result : @"?";
}

@end

provides macro "BACKTRACE_DEPTH(n)" that returns a string listing the methods that called you, useful for logging.
alternately spelled "CALLSTACK_DEPTH(n)"