You need root privileges to access /dev/mem.

To allow access to the GPIO a new device was created called /dev/gpiomem.

/dev/gpiomem can be accessed by members of the gpio group and grants access to the memory used by the GPIO.

I give example code at http://abyz.co.uk/rpi/pigpio/examples.html#Misc_tiny_gpio

You need root privileges to access /dev/mem.

To allow access to the GPIO a new device was created called /dev/gpiomem.

/dev/gpiomem can be accessed by members of the gpio group and grants access to the memory used by the GPIO.

I give example code at http://abyz.me.uk/rpi/pigpio/examples.html#Misc_tiny_gpio