All the way from WWII to his death in 1970 De Gaulle's rank remained that of brigadier general--two stars--, which means that the French Army was full of generals who outranked him. Why wasn't De Gaulle ever promoted to full general--five stars--, let alone to Marshal of France with its seven stars?
God is subtle, but He is not malicious. (Albert Einstein)
Was he still officially in the military during his presidency, or was he a civilian (who's still commander-in-chief, like an American president, but nonetheless a civilian leader)? Does the French constitution allow an active military member to be President? I notice he's still called "General", I'm not sure if Eisenhower was similarly called "General" when he was the (civilian) American President.
At any rate, if he's no longer in the military, he wouldn't be promoted in rank. He'd still be commander-in-chief as President of course (so in practical terms he'd "outrank" everyone else in the military), but so would a President who never served in the military. Different from his titled military rank.
(ETA: Just looked up on Wiki, he was in the French Army until 1944, when he became Chairman of the Provisional Government of the French Republic after the liberation of Paris.)