Detecting if iOS app is run in debugger

Question

I set up my application to either send debugging output to console or a log file. Now, I'd like to decide with in the code whether

• it is run in the debugger (or simulator) and have thus a console window where I would like to read the output directly or if
• there is no console window and thus, the output should be redirected to a file.

Is there a way to determine if the app runs in the debugger?

Answer 1

There's a function from Apple to detect whether a program is being debugged in the Technical Q&A 1361 (entry in Mac library and entry in iOS library; they are identical).

Code from the Technical Q&A:

#include <assert.h> #include <stdbool.h> #include <sys/types.h> #include <unistd.h> #include <sys/sysctl.h>  static bool AmIBeingDebugged(void)     // Returns true if the current process is being debugged (either      // running under the debugger or has a debugger attached post facto). {     int                 junk;     int                 mib[4];     struct kinfo_proc   info;     size_t              size;      // Initialize the flags so that, if sysctl fails for some bizarre      // reason, we get a predictable result.      info.kp_proc.p_flag = 0;      // Initialize mib, which tells sysctl the info we want, in this case     // we're looking for information about a specific process ID.      mib[0] = CTL_KERN;     mib[1] = KERN_PROC;     mib[2] = KERN_PROC_PID;     mib[3] = getpid();      // Call sysctl.      size = sizeof(info);     junk = sysctl(mib, sizeof(mib) / sizeof(*mib), &info, &size, NULL, 0);     assert(junk == 0);      // We're being debugged if the P_TRACED flag is set.      return ( (info.kp_proc.p_flag & P_TRACED) != 0 ); } 

Also pay attention to this note at the end of the Q&A:

Important: Because the definition of the kinfo_proc structure (in <sys/sysctl.h>) is conditionalized by __APPLE_API_UNSTABLE, you should restrict use of the above code to the debug build of your program.

Answer 2

It is possible to instruct the debugger to set environment variables when it launches a process it is about to debug. This can be done in Xcode by going to the menu item Product->Edit Scheme. Then under the Debug scheme's Arguments tab add a new environment variable. The variable should be named "debugger" with the value "true". Then the following code snippet can be used to determine if the debugger launched your process:

NSDictionary* env = [NSProcessInfo processInfo].environment;  if ([env[@"debugger"] isEqual:@"true"]) {     NSLog(@"debugger yes"); } else {     NSLog(@"debugger no"); }