Some extra info about France.
In general, wild camping is forbidden in France, except when stated otherwise. As any other country, France has a number of regional and national natural parks, where "bivouac" (setting up your tent after 7pm and packing it back before 8am) might be allowed. Regulations are specific to each park, and you should get to know it before you enter it and plan to camp there.
A park's regulation can also depend on factors:
- time of the year. eg., some parks only allow it during the summer.
- location within the park. Some parks allow wild camping in general, but not in certain locations due to specific reasons (high natural hazards, water contamination risks, etc.). The areas where wild camping is specifically forbidden are marked by signs on the side of paths accessing said areas. Those signs most likely will only be written in French. In a way, these are "exceptions within exceptions", since camping in natural parks are already an exception within the French law.
- temporary risk (eg, if a huge wildfire is going on).
I have never seen natural parks allowing campfires, or leaving your tent up at the same location at daytime. Might exist but I seriously doubt it. Don't be an idiot and light campfires in the wilderness; bring a stove and a gas can.
If you scroll down a bit on this web page, you will find a map of France with all said parks and their current regulation. I am sorry, everything is in French. If some things are still cryptic through Google translate, feel free to ask me.
Worth noting that like other European countries, France also has a number of free, non-guarded shelters, mostly in mountainous areas. Most of these shelters consist of a small room with a stove for heating, and a second "floor" right below the roof where you can sleep. These shelters are quite rustic, and are mostly maintained on a volunteer basis, by local people, or alpine clubs, for example. You can expect to find wood there for using with the stove. Common practice is bringing back into the shelter as much wood as you have used, obviously. Such shelters are marked with a "empty red house" pictograph on IGN maps (those are the reference maps in France). On this website, you can find more or less updated infos about most shelters, like, if it has been vandalized, water access, a stove, wood, etc. Once again, it's all in French.
As most people already have said, if you are discrete enough, you probably will not get caught even when camping in illegal areas. However, the author's question specifically asked about where it was legal. Obviously, camping on private land is OK if you have the owner's approval.
One last anecdote: during my teenage years, I went hiking for several days in Corsica, where wild camping is strictly forbidden. Putting up your tent close to guarded shelters was allowed, as long as you paid something like 5€/night/person. At the end of the trip, we were all lacking money, and could not pay this fee (yes, we were pretty stupid back then). We ended up playing it fair and going to the guards saying we could not afford it. All of them were OK with that, as long as we stayed close to the shelters. They insisted on warning us that if we were to be found wild camping in forbidden areas, they would fine us hard. They actually did that to another group of people. Moral of the story: just play it fair and remember that the guards' main concern is the protection of the park.