i2c beginner question

Hallo,

I have to collect data from multiple external i2c devices. My question is, what is the correct way?

1: Open i2-device-file, set slave address, read data, close i2c device file and go on with the next one 2: keep the i2c device file open all the time, and change slave address before every access to device 3: ???

greets
Dirk