Rick's France guidebook indicates that all train tickets and reservations before boarding any SNCF train. It has been a few years since I traveled by train in France. Where will I find the validation machine. Will it be on the platform?
The validation machines to punch your paper ticket are at the entrance to each platform. However, electronic tickets printed at home do not need to be punched. The train conductor will scan the bar code. You might have to show your passport and it is a good idea to have the purchasing credit card with you although I've never been bothered on either score.
Explanation: The electronic tickets are all for a specific day and time. The old paper tickets may be used on different trains so are punched to ensure no slick evasions.
The definitive resource re: traveling on French trains, including a picture of the validation machines and a description of where to find them at the head of each platform: http://www.seat61.com/France-trains.htm#.UcEYUKa9LCQ Don't let yourself get distracted and forget to validate! :)
Thanks for the info. I found the machine of the website that you suggested.