CODEWITHSUNDEEP
iosobjective-cdebuggingnsthread
ennuikiller
ennuikiller

Reputation: 46965

Objective-C find caller of method

Is there a way to determine the line of code a certain method was called from?

Upvotes: 91

Views: 36717

Answers (12)

intropedro
intropedro

Reputation: 2804

StackI hope that this helps:

NSString *sourceString = [[NSThread callStackSymbols] objectAtIndex:1];
// Example: 1   UIKit                               0x00540c89 -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 1163
NSCharacterSet *separatorSet = [NSCharacterSet characterSetWithCharactersInString:@" -[]+?.,"];
NSMutableArray *array = [NSMutableArray arrayWithArray:[sourceString  componentsSeparatedByCharactersInSet:separatorSet]];
[array removeObject:@""];

NSLog(@"Stack = %@", [array objectAtIndex:0]);
NSLog(@"Framework = %@", [array objectAtIndex:1]);
NSLog(@"Memory address = %@", [array objectAtIndex:2]);
NSLog(@"Class caller = %@", [array objectAtIndex:3]);
NSLog(@"Function caller = %@", [array objectAtIndex:4]);

Upvotes: 190

Ol Sen
Ol Sen

Reputation: 3348

Back in the days there where no dot syntax in objective-C, so nowadays it could look like.

#define __UGLY__CALLEE__(idx) fprintf(stderr,"\n%s <- %s",__PRETTY_FUNCTION__,(NSThread.callStackSymbols.count>idx?((NSString*)NSThread.callStackSymbols[idx]).UTF8String:"no callStackSymbol with this index"))

just prints what is needed, no extra re-creation of NSArray or Mutables. Apart from the characters to output and an index to chose this lets you repeat with different stack symbols and prints without timestamp. Extra formatting the output does not only loose performance until you get what you need to know about your method calls it also makes the thing kinda un-flexible. And most important not introducing another method call to self just to ask for the last callee.

__UGLY__CALLEE__(1); results in...

-[Some inspectedMethod] <- 1   Appname                             0x00000001000e6cd2 -[SomeCallee method] + 1234

And as it is not pretty - it is called ugly.

Upvotes: 0

Andy Obusek
Andy Obusek

Reputation: 12832

The Swift 4 version of @Geoff H answer for copy and pasting ;] 

let sourceString: String = Thread.callStackSymbols[1]
let separatorSet :CharacterSet = CharacterSet(charactersIn: " -[]+?.,")
var array = Array(sourceString.components(separatedBy: separatorSet))
array = array.filter { $0 != "" }

print("Stack: \(array[0])")
print("Framework:\(array[1])")
print("Memory Address:\(array[2])")
print("Class Caller:\(array[3])")
print("Method Caller:\(array[4])")

Upvotes: 2

Carmelo Gallo
Carmelo Gallo

Reputation: 283

The Swift 3 version of @Geoff H answer for reference:

let sourceString: String = Thread.callStackSymbols[1]
let separatorSet: CharacterSet = CharacterSet(charactersIn: " -[]+?.,")
let array = NSMutableArray(array: sourceString.components(separatedBy: separatorSet))
array.remove("")

print("Stack: \(array[0])")
print("Framework:\(array[1])")
print("Memory Address:\(array[2])")
print("Class Caller:\(array[3])")
print("Method Caller:\(array[4])")

Upvotes: 0

DannyBios
DannyBios

Reputation: 81

@ennuikiller 

//Add this private instance method to the class you want to trace from
-(void)trace
{
  //Go back 2 frames to account for calling this helper method
  //If not using a helper method use 1
  NSArray* stack = [NSThread callStackSymbols];
  if (stack.count > 2)
    NSLog(@"Caller: %@", [stack objectAtIndex:2]);
}

//Add this line to the method you want to trace from
[self trace];

In the output window you will see something like the following.

Caller: 2 MyApp 0x0004e8ae -[IINClassroomInit buildMenu] + 86

You can also parse this string to extract more data about the stack frame.

2 = Thread id
My App = Your app name
0x0004e8ae = Memory address of caller
-[IINClassroomInit buildMenu] = Class and method name of caller
+86 = Number of bytes from the entry point of the caller that your method was called

It was taken from Identify Calling Method in iOS.

Upvotes: 3

Andrew
Andrew

Reputation: 1354

A slightly optimized version of @Roy Kronenfeld's fantastic answer:

- (NSString *)findCallerMethod
{
    NSString *callerStackSymbol = nil;

    NSArray<NSString *> *callStackSymbols = [NSThread callStackSymbols];

    if (callStackSymbols.count >= 2)
    {
        callerStackSymbol = [callStackSymbols objectAtIndex:2];
        if (callerStackSymbol)
        {
            // Stack: 2   TerribleApp 0x000000010e450b1e -[TALocalDataManager startUp] + 46
            NSInteger idxDash = [callerStackSymbol rangeOfString:@"-" options:kNilOptions].location;
            NSInteger idxPlus = [callerStackSymbol rangeOfString:@"+" options:NSBackwardsSearch].location;

            if (idxDash != NSNotFound && idxPlus != NSNotFound)
            {
                NSRange range = NSMakeRange(idxDash, (idxPlus - idxDash - 1)); // -1 to remove the trailing space.
                callerStackSymbol = [callerStackSymbol substringWithRange:range];

                return callerStackSymbol;
            }
        }
    }

    return (callerStackSymbol) ?: @"Caller not found! :(";
}

Upvotes: 3

Geoff H
Geoff H

Reputation: 3247

The Swift 2.0 version of @Intropedro's answer for reference;

let sourceString: String = NSThread.callStackSymbols()[1]

let separatorSet :NSCharacterSet = NSCharacterSet(charactersInString: " -[]+?.,")
let array = NSMutableArray(array: sourceString.componentsSeparatedByCharactersInSet(separatorSet))
array.removeObject("")

print("Stack: \(array[0])")
print("Framework:\(array[1])")
print("Memory Address:\(array[2])")
print("Class Caller:\(array[3])")
print("Method Caller:\(array[4])")

Upvotes: 6

Roy K
Roy K

Reputation: 3319

Just wrote a method that will do this for you:

- (NSString *)getCallerStackSymbol {

    NSString *callerStackSymbol = @"Could not track caller stack symbol";

    NSArray *stackSymbols = [NSThread callStackSymbols];
    if(stackSymbols.count >= 2) {
        callerStackSymbol = [stackSymbols objectAtIndex:2];
        if(callerStackSymbol) {
            NSMutableArray *callerStackSymbolDetailsArr = [[NSMutableArray alloc] initWithArray:[callerStackSymbol componentsSeparatedByString:@" "]];
            NSUInteger callerStackSymbolIndex = callerStackSymbolDetailsArr.count - 3;
            if (callerStackSymbolDetailsArr.count > callerStackSymbolIndex && [callerStackSymbolDetailsArr objectAtIndex:callerStackSymbolIndex]) {
                callerStackSymbol = [callerStackSymbolDetailsArr objectAtIndex:callerStackSymbolIndex];
                callerStackSymbol = [callerStackSymbol stringByReplacingOccurrencesOfString:@"]" withString:@""];
            }
        }
    }

    return callerStackSymbol;
}

Upvotes: 6

Guntis Treulands
Guntis Treulands

Reputation: 4762

Using answer provided by intropedro, I came up with this:

#define CALL_ORIGIN NSLog(@"Origin: [%@]", [[[[NSThread callStackSymbols] objectAtIndex:1] componentsSeparatedByCharactersInSet:[NSCharacterSet characterSetWithCharactersInString:@"[]"]] objectAtIndex:1])

which will simply return me Original class and function:

2014-02-04 16:49:25.384 testApp[29042:70b] Origin: [LCallView addDataToMapView]

p.s. - if function is called using performSelector, result will be:

Origin: [NSObject performSelector:withObject:]

Upvotes: 11

pckill
pckill

Reputation: 3759

You can pass self as one of the arguments to the function and then get the classname of the caller object inside:

+(void)log:(NSString*)data from:(id)sender{
    NSLog(@"[%@]: %@", NSStringFromClass([sender class]), data);
}

//...

-(void)myFunc{
    [LoggerClassName log:@"myFunc called" from:self];
}

This way you can pass it any object that would help you to determine where the problem might be.

Upvotes: 4

Giovanni
Giovanni

Reputation: 257

If it is for debbuging sake, get to the habit of putting a NSLog(@"%s", __FUNCTION__);

As the first line inside each method in your classes. Then you can always know the order of method calls from looking at the debugger.

Upvotes: 5

bbum
bbum

Reputation: 162712

In fully optimized code, there is no 100% surefire way to determine the caller to a certain method. The compiler may employ a tail call optimization whereas the compiler effectively re-uses the caller's stack frame for the callee.

To see an example of this, set a breakpoint on any given method using gdb and look at the backtrace. Note that you don't see objc_msgSend() before every method call. That is because objc_msgSend() does a tail call to each method's implementation.

While you could compile your application non-optimized, you would need non-optimized versions of all of the system libraries to avoid just this one problem.

And this is just but one problem; in effect, you are asking "how do I re-invent CrashTracer or gdb?". A very hard problem upon which careers are made. Unless you want "debugging tools" to be your career, I would recommend against going down this road.

What question are you really trying to answer?

Upvotes: 54

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