I have created a new libray which can be used to log data to a sd card using iostreams and automatically hourly rotating log files.I use this library on the electron to log data coming in from several sources to an sd card. Checkout the example for a complete overview of this library.
It uses the excellent SdFat library.
Together with my FTPFileSender library you get quite a nice system for logging data to an sd card and sending it on request to a server. Checkout the linux scripts in the examples folder of the FTPFileSender project for a script to automatically download several files from log on the SD card.
The library lives at: github and in the Particle library system.
If somebody could look into my problems with pushing a String to an IOSTREAM that would be great.
This is my last new library for now. There might be some rough edges, I just wanted to get them out there, otherwise it would never happen. Appreciate any feedback.