Detect If Your Application Is Running In The Debugger

February 11, 2013

The C function below returns true or false depending on whether or not the application making the call is running in the Xcode debugger. Honestly, I’ve not come up with a scenario when I’ll need this, however, anything that makes system level calls is an interesting study in how things in iOS.

Notice the code below is a C function, not an Objective-C method:

static bool debuggerRunning(void)
{
  int                 junk;
  int                 mib[4];
  struct kinfo_proc   info;
  size_t              size;
 
  info.kp_proc.p_flag = 0;
 
  mib[0] = CTL_KERN;
  mib[1] = KERN_PROC;
  mib[2] = KERN_PROC_PID;
  mib[3] = getpid();
 
  size = sizeof(info);
  junk = sysctl(mib, sizeof(mib) / sizeof(*mib), &info, &size, NULL, 0);
  assert(junk == 0);
 
  // If P_TRACED flag set, debugger running
  return ( (info.kp_proc.p_flag & P_TRACED) != 0 );
}

You can call the above code as follows:

if (debuggerRunning())
  NSLog(@"Debugger running");
else
  NSLog(@"Debugger not running");

This code example is courtesy Apple from their Technical Q&A section.