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

Answer 1

Always good to have different solutions, so here are my two cents:

The idea is to check the stderr filehandle (this is where NSLog prints to). This solution has reliably been working since at least iOS 4 and keeps doing so in iOS 9, both on the simulator and device.

#import <sys/ioctl.h>
#import <sys/param.h>
#if TARGET_IPHONE_SIMULATOR
    #import <sys/conf.h>
#else
// Not sure why <sys/conf.h> is missing on the iPhoneOS.platform.
// It's there on iPhoneSimulator.platform, though. We need it for D_DISK, only:
    #if ! defined(D_DISK)
        #define D_DISK  2
    #endif
#endif

BOOL isDebuggerAttatchedToConsole(void)
{
    // We use the type of the stderr file descriptor
    // to guess if a debugger is attached.

    int fd = STDERR_FILENO;

    // is the file handle open?
    if (fcntl(fd, F_GETFD, 0) < 0) {
        return NO;
    }

    // get the path of stderr's file handle
    char buf[MAXPATHLEN + 1];
    if (fcntl(fd, F_GETPATH, buf ) >= 0) {
        if (strcmp(buf, "/dev/null") == 0)
            return NO;
        if (strncmp(buf, "/dev/tty", 8) == 0)
            return YES;
    }

    // On the device, without attached Xcode, the type is D_DISK (otherwise it's D_TTY)
    int type;
    if (ioctl(fd, FIODTYPE, &type) < 0) {
        return NO;
    }

    return type != D_DISK;
}

Answer 2

The simplest solution actually is

_isDebugging = isatty(STDERR_FILENO);

It isn't exactly the same as telling whether the app is running under debugger, but good enough (even better?) to determine whether the log should be written to disk.