There are a few videos that I have seen lately that have shown officers not knowing the status of their firearms, pistols specifically. Bill Rapier, of amtacshooting.com, always goes over the proper procedure of checking if your firearm. If you have not trained with Bill, you should definitely seek out a class of his and learn the mindset behind firearm manipulations.
First video comes out of Chicago PD. Officers are attacked by a man who overcame tasers and had a knife. The officer in the video attempts to shoot the male but his pistol doesn't sound like it was loaded.
Next video is out of Roy City PD, starts at around the 6:45 mark, the officer sends a K9 out to grab a guy who fled from the officer during a pursuit. The officer goes to shoot the male but the gun either malfunctions or isn't loaded. He tap/racks and gets a click. Then rips the magazine out, racks again and puts rounds on target effectively. The officer's K9 does and survives.